Isokinetic knee strength across physical activity levels: A gender-based comparison in young adults

Abstract

Background

While isokinetic knee strength profiles have been widely studied in athletes, data based on physical activity levels in young adult men and women remain limited.

Objective

This study aimed to determine knee isokinetic strength values according to physical activity level, with a focus on inactive (sedentary) individuals.

Methods

A total of 84 participants (42 females, 42 males) were divided three groups based on the International Physical Activity Questionnaire-Short Form (IPAQ-SF): inactive, minimally active, and active (12–15 per subgroup). Unilateral knee strength was assessed using isokinetic dynamometry at 60°/s and 180°/s. Two-way ANOVA was used to evaluate differences across groups, and gender comparisons were analysed using a t-test.

Results

Men demonstrated higher absolute strength values than women in all activity levels. In inactive and minimally active groups, there were no significant gender differences in extensor relative peak moment (PM/kg), peak work (PW/kg), or peak power (PPw/kg) (p > 0.05). However, flexor values showed significant gender differences (p < 0.05). In the active group, all relative strength values differed significantly between genders.

Conclusion

The absence of gender difference in extensor strength of inactive individuals suggests their use as a normative references for this cohort. Gender differences became more pronounced with increased physical activity.

Keywords

Isokinetic muscle strength normative data activity levels

1. Introduction

The term physical inactivity (PA) describes an inadequate level of activity according to physical activity guidelines.¹ However, the sedentary behaviour, defined as a minimal energy consumption (around 1.5 METs), for example sitting, lying down, napping for long periods of day.¹ According to data from the National Health and Nutrition Examination Survey (NHANES), both children and adults in the United States spend an average of approximately 7.7 h per day in a waking state.² This time is mostly spent in sedentary behaviours such as watching television, playing passive video games and computer games.² In large population-based studies, physical activity level assessment has been performed by using self-survey application because these are more practical, economical and non-invasive.³ Commonly, the version of the Short Form of the International Physical Activity Questionnaire (IPAQ-SF) has been modified for multi-cultural populations and is highly valued as the most widely used questionnaire.⁴

The results of IPAQ-SF are calculated as walking, moderate and vigorous intensity PA and total PA score according to different physical activity levels. In addition, low, moderate and high PA are also determined as weekly energy expenditure and metabolic equivalents (METs min/wk-1). Up to date, the measurement of physical activity level has been addressed simultaneously with accelerometer,⁵ maximal oxygen uptake (VO₂max),⁶ muscular endurance⁷ has been determined according to the IPAQ-SF score in large populations. All these studies have shown a positive correlation between physical measurements and IPAQ-SF results. In addition, these studies related the validity of IPAQ-SF with VO₂max^6–8 and muscular strength endurance⁷ and found significant correlations.³ The results of the IPAQ-SF not only correlated with cardiovascular endurance and muscular strength, but also with flexibility and trunk muscular endurance.⁹ In addition, the level of physical performance and inactivity affects muscle function. Indeed, skeletal muscle strength values are not only functionally important but also key to negative outcomes such as musculoskeletal diseases, disability and poor quality of life.¹⁰ Reference values for lower extremity muscle strength have already been established in different populations such as athletes,¹¹ children,¹² elderly people¹³ or specialised groups. Moreover, normative data also show that isokinetic muscle strength values vary depending on the sport type of the athletes.¹⁴

However, to the best of our knowledge, no previous study has widely characterized the relationship of IPAQ-SF questionnaire results with isokinetic muscle strength values. In sports science research, participants are typically categorized into groups such as controls, athletes, or physically active individuals when undergoing isokinetic measurement tests. However, these classifications are often not based on objective strength levels or peak moment values. Therefore, there is a need for reference measurement ranges that allow for a more scientific classification of muscle strength levels using isokinetic assessments. Accordingly, the aim of this study is to determine the relative differences in muscle strength between physically active and inactive individuals, based on isokinetic dynamometry data obtained from participants classified into activity groups according to IPAQ. Furthermore, although isokinetic muscle strength has been widely studied across various sports disciplines, there is a lack of isokinetic data, especially inactive sedentary individuals. Also, sedentary behaviour is increasingly common among young adults and is associated with musculoskeletal weaknesses that may predispose individuals to injury or functional limitations. This study aims to address this gap by providing reference values for isokinetic knee strength in young men and women with varying physical activity levels, with a particular focus on sedentary individuals.

2. Methods

2.1. The study procedure and participants

Study data were collected on separate days. First, participants’ physical activity levels were determined using the self-administered IPAQ-SF questionnaire.³ Then, the physical compositions of the participants were measured and right leg isokinetic knee muscle strength tests were performed.

A total of 84 participants (42 females and 42 males) were included in the study and categorized into three groups based on their physical activity levels according to the IPAQ-SF: inactive (15 females, 12 males), minimally active (12 females, 15 males), and active (15 females, 15 males). All participants had no musculoskeletal or neurological injuries or disabilities or use any anti-inflammatory drugs or any treatments during the research period.

Isokinetic test measurements were conducted on the right leg at the similar time of the day (±2 h) for all participants. The right leg was chosen for standardization purposes and because it is commonly the dominant limb in the general population, which helps reduce variability related to limb dominance. Previous studies have also commonly used the right leg in isokinetic testing for consistency and comparability.^15,16 The same researcher carried out all measurements.

2.2 Assessment of the physical activity level using IPAQ-SF

The Turkish version of IPAQ-SF¹⁷ was used to determine the physical activity level of the participants. The physical activity levels of the participants in the last 7 days were assessed in accordance with the scale. This scale includes seven questions assessing the duration of sitting, walking, moderate and vigorous activity. The total score is calculated by summing the scores from walking, moderate and vigorous activity. The IPAQ-SF final scores are reported in units of MET minutes-week-1. This calculating protocol for walking = (3.3 × walking minutes × walking days); moderate activity = (4.0 × moderate activity minutes × moderate activity days); and vigorous activity = (8.0 × vigorous activity minutes × vigorous activity days). Based on the total PA score, participants are categorized as an “Active, Minimally Active and Inactive person”. The sitting score is calculated separately, it indicates sedentary behaviour.^4,17

2.3 Isokinetic test evaluation

The Isokinetic test, concentric/concentric active mode knee flexion and extension strength of the participants were evaluated by ISOMED 2000 (D.& R. Ferstl Gmbh, Hemau, Germany). Prior to the test, the participants were instructed about the evaluation process and visual feedback was also provided. All participants were verbally motivated for maximum effort. Participants were allowed to hold the handles on the edge of the seat and asked how to stop the test in case of an emergency. Knee, hip and waist positions were automatically adjusted by software to position the hips at the correct angle. The upper part of the body, shoulders, hips and upper leg were fixed with a belt to stabilise them. The distal part of the movable arm for the lower leg is attached to the lateral malleolus of the ankle. The swivel axis in the knee is positioned with the lateral femoral condyle of the knee joint at 90° knee flexion. The range of motion of the knee was adjusted between 0 and 90° with mechanical limits. Also, the effect of gravity correction was calculated before the test. The test protocol was performed at two different angular speeds, from slow to fast (60°/s and 180°/s) with flexion/extension and concentric/concentric mode. A familiarization session was conducted one day prior to the actual isokinetic testing, immediately following the completion of physical measurements. During this session, participants were positioned on the isokinetic dynamometer in the standard seated posture to ensure proper alignment and test readiness. After performing several submaximal trial repetitions at each angular velocity, participants completed five maximal voluntary contractions for both knee extension and flexion. This session aimed to accustom participants to the test procedures, angular velocities, and the requirement for maximal effort. To minimize potential measurement variability, all assessments were administered by the same experienced examiner. The participants actual test performed at the 60°/s 6 repetitions and 20 repetitions at the 180°/s angular velocity of knee flexion/extension. All isokinetic muscle strength parameters were analysed at the end of the test.

2.4 Statistical analysis

The data were analysed using the SPSS 30.0 software package. Descriptive data were expressed as number, minimum, maximum, mean and standard deviation. A priori power analysis was performed using G*Power software (version 3.1) to determine the required sample size for the two-way ANOVA design (3 activity levels × 2 gender = 6 groups). Assuming a large effect size (Cohen's f = 0.40), an alpha level of 0.05 and a power of 0.80, the analysis indicated that a total of 52 participants would be sufficient to detect statistically significant differences. This corresponds to a minimum of 9 participants per group. Accordingly, the study was designed with three physical activity groups of 12 to 15 participants each. Descriptive statistics were calculated for all variables. A two-way analysis of variance (ANOVA) was conducted to assess the main effects of gender (male, female) and physical activity level (inactive, minimally active, active), as well as their interaction, on isokinetic knee strength variables. The significance level was set at p < 0.05. The two-way ANOVA revealed significant main effects for both gender and physical activity level, indicating that each factor independently influenced strength outcomes. However, the interaction effect between gender and physical activity level was not statistically significant (p > 0.05), suggesting that the effect of gender on knee strength did not vary across different activity levels. In line with standard statistical practices, and due to the absence of a significant interaction, simple comparisons were performed to further investigate the main effect of gender. Independent samples t-tests were used to compare male and female participants within each physical activity group. This approach is methodologically appropriate for identifying the source of main effects when interaction terms are not significant.^18,19

3. Results

In Table 1, participants were categorised as inactive, minimally active and active according to IPAQ-SF scores. In all groups, men had significantly higher body weight and height than women (p < 0.05), while women in the active group had significantly higher IPAQ scores (p < 0.05). (Table 1).

Table 1.
Classification of groups according to international physical activity questionnaire-short form scale scores.

Age (y) Height (cm) Weight (kg) IPAQ-SF score

Groups n Min. Max. $\bar{X}$ Min. Max. $\bar{X}$ Min. Max. $\bar{X}$ Min. Max. $\bar{X}$

Inactive Female 15 20 23 21.40 154 175 164 45 75 55.54 00 594 214.67

Male 12 20 28 22.75 167 183 176.33 60 115 79.70 00 594 162.00

Minimally Active Female 12 20 23 20.66 157 180 168.66 49 80 62.65 780 2772 1557.76

Male 15 20 25 21.50 167 186 175.14 58 93 75.40 676 2950 1902.42

Active Female 15 18 23 20.93 157 178 167.06 48 77 58.40 3012 13,500 6328.66

Male 15 20 28 22.13 171 200 184.13 68 109 85.66 3177 6657 4555.86

			Age (y)	Height (cm)	Weight (kg)	IPAQ-SF score
Inactive	Female	15	20	23	21.40	154	175	164	45	75	55.54	00	594	214.67
Male	12	20	28	22.75	167	183	176.33	60	115	79.70	00	594	162.00
Minimally Active	Female	12	20	23	20.66	157	180	168.66	49	80	62.65	780	2772	1557.76
Male	15	20	25	21.50	167	186	175.14	58	93	75.40	676	2950	1902.42
Active	Female	15	18	23	20.93	157	178	167.06	48	77	58.40	3012	13,500	6328.66
Male	15	20	28	22.13	171	200	184.13	68	109	85.66	3177	6657	4555.86

IPAQ-SF: International physical activity questionnaire-short form.

The mean values of isokinetic muscle strength parameters (moment, work and power) according to gender and activity level are presented in Table 2. According to the two way-ANOVA analysis, gender and physical activity level had a significant effect on all parameters for both extensor and flexor muscles (p < 0.05) Two-way ANOVA revealed significant main effects of gender and physical activity level on all isokinetic muscle strength variables, including peak moment, average moment, total moment, peak work, average work, total work, peak power, and average power at both angular velocities (60°/s and 180°/s) (p < .001 for most comparisons). These findings indicate that both gender and physical activity level independently influence muscle performance (Table 3).

Table 2.

Mean ± SD values of isokinetic muscle performance variables (moment, work and power) according to gender and activity level.

			Inactive^a (n = 27)		Minimally Active^b (n = 27)		Active^c (n = 30)
			Female (n = 15)	Male (n = 12)	Female (n = 12)	Male (n = 15)	Female (n = 15)	Male (n = 15)
Angular Velocity & Isokinetic Muscle StrenghtVariables			Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
60^o/s	Peak Moment (Nm)	Extansor	112.40 ± 15.03	185.41 ± 35.76	147.00 ± 31.12	197.50 ± 33.03	141.0 ± 22.17	252.20 ± 46.01
	Peak Moment (Nm)	Flexor	55.13 ± 7.5	111.58 ± 22	81.33 ± 22.01	118.28 ± 24.02	82.93 ± 15.40	163.33 ± 27.58
	Avarage Moment (Nm)	Extansor	101.54 ± 16.10	167.3 ± 37.72	137.46 ± 28.66	172.08 ± 47.56	128.43 ± 23.28	232.59 ± 43.71
	Avarage Moment (Nm)	Flexor	50.16 ± 7.53	98.78 ± 24.91	74.96 ± 19.94	108.96 ± 27.07	76.38 ± 14.68	150.36 ± 27.63
	Total Moment (Nm)	Extansor	608.13 ± 96.41	1004.4 ± 227.1	824.91 ± 171.92	1019.21 ± 320.3	770.66 ± 139.68	1424.60 ± 276.3
	Total Moment (Nm)	Flexor	299.26 ± 47.07	592.83 ± 149.4	732.41 ± 962.51	653.85 ± 162.50	458.46 ± 88.13	903.46 ± 166.85
	Peak Work (J)	Extansor	96.46 ± 16.07	148.33 ± 26.71	121.66 ± 24.92	157.07 ± 26.31	118.80 ± 16.59	200.20 ± 38.62
	Peak Work (J)	Flexor	59.33 ± 9.75	111.5 ± 19.94	88.33 ± 23.51	119.07 ± 21.23	88.66 ± 14.04	157.06 ± 17.98
	Avarage Work (J)	Extansor	87.26 ± 14.63	134.5 ± 27.07	113.58 ± 24.28	145.28 ± 23.27	110.06 ± 17.15	187.93 ± 38.57
	Avarage Work (J)	Flexor	54.06 ± 10.51	96.08 ± 19.97	79.41 ± 22.67	107.35 ± 20.95	81.33 ± 13.08	144.53 ± 17.77
	Total Work (J)	Extansor	523 ± 88.87	808.5 ± 164.24	683.25 ± 145.37	1021.85 ± 583.8	660.26 ± 102.59	1128.20 ± 232
	Total Work (J)	Flexor	325.6 ± 61.7	575.8 ± 120.21	477.75 ± 134.55	613.64 ± 1 69.27	488.0 ± 79.06	868.73 ± 106.77
	Peak Power (Watt)	Extansor	65.20 ± 11.38	106.75 ± 21.20	86.08 ± 20.17	116.07 ± 24.83	82.60 ± 14.42	151.60 ± 27.53
	Peak Power (Watt)	Flexor	38.46 ± 6.03	75.25 ± 13.60	57.16 ± 14.32	76.67 ± 28.33	56.86 ± 10.09	113.73 ± 19.26
	Avarage Power (Watt)	Extansor	57.26 ± 9.81	96.90 ± 22.33	79.67 ± 18.51	107.58 ± 22.41	74.93 ± 14.25	142.30 ± 29.55
	Avarage Power (Watt)	Flexor	34.85 ± 6.15	63.62 ± 16.56	51.25 ± 12.52	76.0 ± 19.11	50.63 ± 10.51	102.88 ± 17.21
180^o/s	Peak Moment (Nm)	Extansor	91 ± 14.35	150.66 ± 40.81	121.58 ± 21.61	165.92 ± 33.81	121.46 ± 19.36	222.20 ± 30.01
	Peak Moment (Nm)	Flexor	47.53 ± 9.24	98.58 ± 19.84	68.0 ± 17.77	102.35 ± 21.53	72.40 ± 14.80	139.66 ± 28.03
	Avarage Moment (Nm)	Extansor	74.80 ± 11.24	121.99 ± 32.60	96.04 ± 15.38	135.45 ± 29.98	97.18 ± 16.27	178.09 ± 24.12
	Avarage Moment (Nm)	Flexor	39.13 ± 8.30	77.68 ± 16.70	63.17 ± 23.92	84.65 ± 16.90	59.03 ± 13.02	108.60 ± 22.04
	Total Moment (Nm)	Extansor	1496 ± 224.81	2440 ± 652.18	1920.83 ± 3 07.7	2709.07 ± 599.7	1943 ± 324.68	3561.86 ± 260.4
	Total Moment (Nm)	Flexor	782.60 ± 166.06	1553.75 ± 334.11	1120.58 ± 322.7	1689.78 ± 340.6	1180.86 ± 260.4	2172.13 ± 440.9
	Peak Work (J)	Extansor	78 ± 14.59	128.08 ± 34.97	102.0 ± 20.48	137.42 ± 25.82	103.26 ± 18.17	181.20 ± 26.03
	Peak Work (J)	Flexor	45.26 ± 8.03	91.91 ± 17.7	63.83 ± 17.37	95.85 ± 22.09	69.60 ± 12.18	129.26 ± 17.87
	Avarage Work (J)	Extansor	59.80 ± 11.36	102.75 ± 26.40	76.08 ± 14.58	113.35 ± 22.19	79.26 ± 15.32	146.20 ± 18.02
	Avarage Work (J)	Flexor	35.13 ± 7.52	71.41 ± 14.62	53.16 ± 14.76	78.71 ± 16.14	56.40 ± 10.98	101.40 ± 16.25
	Total Work (J)	Extansor	1199 ± 223.73	2058 ± 528.45	1434.0 ± 488.43	2271.5 ± 444.28	1594.2 ± 307.12	3127.2 ± 866.6
	Total Work (J)	Flexor	707.53 ± 150.8	1434.75 ± 295.34	1065.58 ± 296.7	1579.85 ± 317.3	1132.26 ± 217.3	2032.26 ± 321.1
	Peak Power (Watt)	Extansor	95.66 ± 17.30	160.50 ± 46.20	125.41 ± 26.60	171.0 ± 32.83	127.26 ± 32.91	226.86 ± 32.91
	Peak Power (Watt)	Flexor	53.73 ± 11.20	106.33 ± 20.32	75.33 ± 19.27	114.0 ± 24.33	82.35 ± 15.72	155.40 ± 23.66
	Avarage Power (Watt)	Extansor	73.17 ± 13.95	125.9 ± 33.02	92.93 ± 18.01	140.73 ± 2.64	98.35 ± 20.19	176.08 ± 28.54
	Avarage Power (Watt)	Flexor	43.47 ± 11.64	82.97 ± 18.89	60.4 ± 16.45	91.86 ± 17.10	64.95 ± 13.07	118.55 ± 20.0

Table 3.

Two-Way ANOVA results of gender, activity level and interaction on isokinetic muscle performance variables (moment, work and power).

			Gender	Activity Group	Activity Level × Gender Interaction
Angular Velocity & Isokinetic Muscle Strength Variables			F (p)	F (p)	F (p)
60^o/s	Peak Moment (Nm)	Extansor	123.180 (<.001)	15.758 (<.001)	6.489 (0.002)
	Peak Moment (Nm)	Flexor	161.177 (<.001)	26.545 (<.001)	7.736 (<.001)
	Avarage Moment (Nm)	Extansor	79.859 (<.001)	12.661 (<.001)	7.089 (0.001)
	Avarage Moment (Nm)	Flexor	122.309 (<.001)	23.525 (<.001)	6.296 (0.003)
	Total Moment (Nm)	Extansor	73.590 (<.001)	12.746 (<.001)	7.727 (<.001)
	Total Moment (Nm)	Flexor	6.770 (0.011)	3.562 (0.033)	3.366 (0.040)
	Peak Work (J)	Extansor	96.090 (<.001)	14.470 (<.001)	5.660 (0.005)
	Peak Work (J)	Flexor	161.296 (<.001)	30.623 (<.001)	7.608 (<.001)
	Avarage Work (J)	Extansor	87.228 (<.001)	15.976 (<.001)	6.050 (0.004)
	Avarage Work (J)	Flexor	129.176 (<.001)	32.376 (<.001)	7.057 (0.002)
	Total Work (J)	Extansor	35.059 (<.001)	5.233 (0.007)	0.816 (0.446)
	Total Work (J)	Flexor	100.212 (<.001)	27.740 (<.001)	7.818 (<.001)
	Peak Power (Watt)	Extansor	105.864 (<.001)	16.097 (<.001)	6.670 (0.002)
	Peak Power (Watt)	Flexor	102.960 (<.001)	20.893 (<.001)	8.592 (<.001)
	Avarage Power (Watt)	Extansor	99.343 (<.001)	16.777 (<.001)	6.944 (0.002)
	Avarage Power (Watt)	Flexor	125.064 (<.001)	26.183 (<.001)	7.712 (<.001)
180^o/s	Peak Moment (Nm)	Extansor	124.715 (<.001)	24.122 (<.001)	7.851 (<.001)
	Peak Moment (Nm)	Flexor	140.772 (<.001)	20.976 (<.001)	4.979 (0.009)
	Avarage Moment (Nm)	Extansor	124.510 (<.001)	21.328 (<.001)	6.733 (0.002)
	Avarage Moment (Nm)	Flexor	90.906 (<.001)	15.231 (<.001)	4.573 (0.013)
	Total Moment (Nm)	Extansor	124.613 (<.001)	21.317 (<.001)	6.746 (0.002)
	Total Moment (Nm)	Flexor	120.336 (<.001)	17.776 (<.001)	3.011 (0.055)
	Peak Work (J)	Extansor	107.112 (<.001)	19.304 (<.001)	5.773 (0.005)
	Peak Work (J)	Flexor	163.258 (<.001)	25.947 (<.001)	4.957 (0.009)
	Avarage Work (J)	Extansor	146.041 (<.001)	20.909 (<.001)	5.212 (0.008)
	Avarage Work (J)	Flexor	140.075 (<.001)	24.961 (<.001)	3.532 (0.034)
	Total Work (J)	Extansor	88.142 (<.001)	14.887 (<.001)	4.413 (0.020)
	Total Work (J)	Flexor	142.387 (<.001)	25.123 (<.001)	3.514 (0.035)
	Peak Power (Watt)	Extansor	106.368 (<.001)	18.210 (<.001)	5.577 (0.005)
	Peak Power (Watt)	Flexor	161.505 (<.001)	28.706 (<.001)	5.503 (0.006)
	Avarage Power (Watt)	Extansor	123.146 (<.001)	17.123 (<.001)	3.117 (0.050)
	Avarage Power (Watt)	Flexor	132.308 (<.001)	21.627 (<.001)	3.307 (0.042)

* = p < 0.05; ** = p < 0.01.

In Table 4, at both speeds, male participants demonstrated consistently higher relative strength values compared to females across all physical activity levels. This trend was observed in both extensor and flexor muscle groups, with the most notable differences evident in the flexor parameters. Two-way ANOVA results, at both 60°/s and 180°/s angular velocities, significant main effects of gender and physical activity level were observed across all relative strength variables (p < .001), for both extensor and flexor muscle groups (Table 5). Importantly, no significant interaction effects were found between gender and activity level for any of the variables (all p > 0.17). For instance, at 60°/s, interaction p-values ranged from 0.224 to 0.581, and at 180°/s, from 0.221 to 0.730. This suggests that the impact of gender on relative muscle strength did not vary significantly across different physical activity levels. In other words, gender-related differences in relative strength were consistent regardless of activity level. The strongest gender effects were observed in flexor strength, particularly at 180°/s, where peak moment/body weight yielded F = 20.871 (p < .001), and peak work/body weight showed F = 25.667 (p < .001). Similarly, activity level had the largest effect on extensor peak moment/body weight at 180°/s (F = 18.947, p < .001), reflecting greater strength development in more active individuals. These results further support the conclusion that while both gender and activity level significantly affect relative isokinetic muscle performance, they act independently, and their combined influence is not interactive.

Table 4.

Mean ± SD values of isokinetic muscle performance variables (relative moment, work and power) according to gender and activity level.

			Inactive^a (n = 27)		Minimally Active^b (n = 27)		Active^c (n = 30)
			Female (n = 15)	Male (n = 12)	Female (n = 12)	Male (n = 15)	Female (n = 15)	Male (n = 15)
Angular Velocity & Isokinetic Muscle Strength Variebles			Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD	Mean ± SD
60^o/s	Peak Moment/ Body Weight (Nm/kg)	Extansor	1.95 ± 0.50	2.26 ± 0.26	2.34 ± 0.51	2.62 ± 0.34	2.39 ± 0.35	2.90 ± 0.52
	Peak Moment/ Body Weight (Nm/kg)	Flexor	0.99 ± 0.24	1.37 ± 0.32	1.30 ± 0.43	1.58 ± 0.31	1.39 ± 0.26	1.89 ± 0.43
	Peak Work/ Body Weight (J/kg)	Extansor	1.75 ± 0.31	1.89 ± 0.30	1.94 ± 0.35	2.09 ± 0.26	2.04 ± 0.27	2.34 ± 0.36
	Peak Work/ Body Weight (J/kg)	Flexor	1.09 ± 0.23	1.44 ± 0.30	1.43 ± 0.42	1.58 ± 0.23	1.53 ± 0.25	1.86 ± 0.30
	Peak Power/ Body Weight (Watt/kg)	Extansor	1.19 ± 0.25	1.34 ± 0.13	1.38 ± 0.30	1.54 ± 0.26	1.42 ± 0.21	1.77 ± 0.28
	Peak Power/ Body Weight (Watt/kg)	Flexor	0.70 ± 0.15	0.96 ± 0.18	0.92 ± 0.26	1.03 ± 0.36	0.98 ± 0.19	1.34 ± 0.27
180^o/s	Peak Moment/ Body Weight (Nm/kg)	Extansor	1.63 ± 0.24	1.83 ± 0.33	1.91 ± 0.37	2.18 ± 0.33	2.07 ± 0.34	2.58 ± 0.49
	Peak Moment/ Body Weight (Nm/kg)	Flexor	0.87 ± 0.29	1.21 ± 0.20	1.06 ± 0.35	1.34 ± 0.25	1.22 ± 0.28	1.61 ± 0.48
	Peak Work/ Body Weight (J/kg)	Extansor	1.41 ± 0.25	1.61 ± 0.34	1.63 ± 0.31	1.83 ± 0.27	1.78 ± 0.33	2.13 ± 0.31
	Peak Work/ Body Weight (J/kg)	Flexor	0.82 ± 0.18	1.17 ± 0.21	1.04 ± 0.36	1.27 ± 0.25	1.20 ± 0.23	1.54 ± 0.34
	Peak Power/ Body Weight (Watt/kg)	Extansor	1.74 ± 0.31	2.01 ± 0.43	2.01 ± 0.40	2.27 ± 0.35	2.19 ± 0.42	2.67 ± 0.40
	Peak Power/ Body Weight (Watt/kg)	Flexor	0.98 ± 0.24	1.45 ± 0.24	1.23 ± 0.40	1.52 ± 0.29	1.42 ± 0.30	1.85 ± 0.43

Table 5.

Two-Way ANOVA results of gender, activity level and interaction on isokinetic muscle performance variables (relative moment, work and power).

			Gender	Activity Group	Activity Level × Gender Interaction
Angular Velocity & Isokinetic Muscle Strength Variables			F (p)	F (p)	F (p)
60^o/s	Peak Moment/ Body Weight (Nm/kg)	Extansor	14.902 (<.001)	11.224 (<.001)	0.548 (0.581)
	Peak Moment/ Body Weight (Nm/kg)	Flexor	26.306 (<.001)	12.752 (<.001)	0.733 (0.484)
	Peak Work/ Body Weight (J/kg)	Extansor	7.526 (0.008)	9.731 (<.001)	0.573 (0.566)
	Peak Work/ Body Weight (J/kg)	Flexor	18.375 (<.001)	14.807 (<.001)	0.874 (0.421)
	Peak Power/ Body Weight (Watt/kg)	Extansor	16.381 (<.001)	12.043 (<.001)	1.526 (0.224)
	Peak Power/ Body Weight (Watt/kg)	Flexor	19.549 (<.001)	12.253 (<.001)	1.803 (0.172)
180^o/s	Peak Moment/ Body Weight (Nm/kg)	Extansor	15.888 (<.001)	18.947 (<.001)	1.540 (0.221)
	Peak Moment/ Body Weight (Nm/kg)	Flexor	20.871 (<.001)	9.258 (<.001)	0.314 (0.713)
	Peak Work/ Body Weight (J/kg)	Extansor	13.388 (<.001)	14.807 (<.001)	0.614 (0.544)
	Peak Work/ Body Weight (J/kg)	Flexor	25.667 (<.001)	13.450 (<.001)	0.359 (0.699)
	Peak Power/ Body Weight (Watt/kg)	Extansor	15.788 (<.001)	14.616 (<.001)	0.693 (0.503)
	Peak Power/ Body Weight (Watt/kg)	Flexor	24.920 (<.001)	14.497 (<.001)	0.316 (0.730)

* = p < 0.05; ** = p < 0.01.

In Table 6, according to gender comparison by t-test results indicated that, in the inactive group, no statistically significant gender differences were observed in extensor strength across all variables at either velocity (p > 0.05), though small to moderate effect sizes were noted (Cohen's d = −0.43 to −0.75). In contrast, flexor strength values were significantly higher in males for all variables and velocities (p < 0.01), with large effect sizes (Cohen's d = −1.30 to −1.68), indicating marked gender disparities in flexor strength among sedentary individuals. In minimally active participants, gender differences remained non-significant in most extensor variables (p > 0.05), with moderate effect sizes. However, significant differences were found in flexor strength, particularly at 180°/s for PM/BW and PPw/BW (p = 0.029 and p = 0.045, respectively), again favoring males (Cohen's d = −0.83). In the active group, statistically significant gender differences were present across all variables and muscle groups at both angular velocities (p < 0.01 for most comparisons). Males demonstrated consistently higher relative strength than females in both extensors and flexors. Effect sizes were large (Cohen's d = −0.99 to −1.51), highlighting the pronounced influence of gender on muscle strength among highly active individuals.

Table 6.

Comparison of PM/BW, PW/BW and PPw/BW mean values between groups according to gender.

Activity Level & Isokinetic Muscle Strength Variables		Female Mean ± SD	Male Mean ± SD	t	p	Cohen d
Inactive
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Extansor	1.95 ± 0.50	2.26 ± 0.26	3.280	0.062	−0.75
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Flexor	0.99 ± 0.24	1.37 ± 0.32	12.313	0.002**	−1.35
Peak Moment/ Body Weight (Nm/kg) 180^o/s	Extansor	1.63 ± 0.24	1.83 ± 0.33	−1.689	0.091	−0.69
Peak Moment/ Body Weight (Nm/kg) 180^o/s	Flexor	0.87 ± 0.29	1.21 ± 0.20	11.792	0.002**	−1.33
Peak Work/ Body Weight (J/kg) 60^o/s	Extansor	1.75 ± 0.31	1.89 ± 0.30	−1.119	0.274	−0.43
Peak Work/ Body Weight (J/kg) 60^o/s	Flexor	1.09 ± 0.23	1.44 ± 0.30	−3.366	0.001**	−1.30
Peak Work/ Body Weight (J/kg)180^o/s	Extansor	1.41 ± 0.25	1.61 ± 0.34	−1.729	0.096	−0.67
Peak Work/ Body Weight (J/kg)180^o/s	Flexor	0.82 ± 0.18	1.17 ± 0.21	−4.462	0.001**	−1.68
Peak Power/ Body Weight (Watt/kg) 60^o/s	Extansor	1.19 ± 0.25	1.34 ± 0.13	−2.009	0.057	−0.73
Peak Power/ Body Weight (Watt/kg) 60^o/s	Flexor	0.70 ± 0.15	0.96 ± 0.18	−4.009	0.001**	−1.55
Peak Power/ Body Weight (Watt/kg) 180^o/s	Extansor	1.74 ± 0.31	2.01 ± 0.43	−1.926	0.066	−0.74
Peak Power/ Body Weight (Watt/kg) 180^o/s	Flexor	0.98 ± 0.24	1.45 ± 0.24	−3.921	0.001**	−1.51
Minimally Active
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Extansor	2.34 ± 0.51	2.62 ± 0.34	2.799	0.107	−0.65
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Flexor	1.30 ± 0.43	1.58 ± 0.31	3.750	0.064	−0.73
Peak Moment Body Weight (Nm/kg) 180^o/s	Extansor	1.91 ± 0.37	2.18 ± 0.33	3.727	0.065	−0.69
Peak Moment Body Weight (Nm/kg) 180^o/s	Flexor	1.06 ± 0.35	1.34 ± 0.25	5.361	0.029*	−0.83
Peak Work/ Body Weight (J/kg) 60^o/s	Extansor	1.94 ± 0.35	2.09 ± 0.26	−1.183	0.249	−0.46
Peak Work/ Body Weight (J/kg) 60^o/s	Flexor	1.43 ± 0.42	1.58 ± 0.23	−1.179	0.250	−0.46
Peak Work/ Body Weight (J/kg)180^o/s	Extansor	1.63 ± 0.31	1.83 ± 0.27	−1.669	0.108	−0.65
Peak Work/ Body Weight (J/kg)180^o/s	Flexor	1.04 ± 0.36	1.27 ± 0.25	−1.902	0.069	−0.74
Peak Power/ Body Weight (Watt/kg) 60^o/s	Extansor	1.38 ± 0.30	1.54 ± 0.26	−1.424	0.167	−0.56
Peak Power/ Body Weight (Watt/kg) 60^o/s	Flexor	0.92 ± 0.26	1.03 ± 0.36	−0.854	0.402	−0.33
Peak Power/ Body Weight (Watt/kg) 180^o/s	Extansor	2.01 ± 0.40	2.27 ± 0.35	−1.797	0.085	−0.70
Peak Power/ Body Weight (Watt/kg) 180^o/s	Flexor	1.23 ± 0.40	1.52 ± 0.29	−2.120	0.045*	−0.83
Active
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Extansor	2.39 ± 0.35	2.90 ± 0.52	9.680	0.004**	−1.13
Peak Moment/ Body Weight (Nm/kg) 60^o/s	Flexor	1.39 ± 0.26	1.89 ± 0.43	14.836	0.001**	−1.40
Peak Moment/ Body Weight (Nm/kg) 180^o/s	Extansor	2.07 ± 0.34	2.58 ± 0.49	10.836	0.003**	−1.20
Peak Moment/ Body Weight (Nm/kg) 180^o/s	Flexor	1.22 ± 0.28	1.61 ± 0.48	7.449	0.011*	−0.99
Peak Work/ Body Weight (J/kg) 60^o/s	Extansor	2.04 ± 0.27	2.34 ± 0.36	−2.484	0.019*	−0.90
Peak Work/ Body Weight (J/kg) 60^o/s	Flexor	1.53 ± 0.25	1.86 ± 0.30	−3.239	0.003**	−1.18
Peak Work/ Body Weight (J/kg)180^o/s	Extansor	1.78 ± 0.33	2.13 ± 0.31	−2.951	0.006**	−1.07
Peak Work/ Body Weight (J/kg)180^o/s	Flexor	1.20 ± 0.23	1.54 ± 0.34	−3.146	0.004**	−1.14
Peak Power/ Body Weight (Watt/kg) 60^o/s	Extansor	1.42 ± 0.21	1.77 ± 0.28	−3.888	0.001**	−1.42
Peak Power/ Body Weight (Watt/kg) 60^o/s	Flexor	0.98 ± 0.19	1.34 ± 0.27	−4.141	0.001**	−1.51
Peak Power/ Body Weight (Watt/kg) 180^o/s	Extansor	2.19 ± 0.42	2.67 ± 0.40	−3.172	0.004**	−1.15
Peak Power/ Body Weight (Watt/kg) 180^o/s	Flexor	1.42 ± 0.30	1.85 ± 0.43	−3.104	0.004**	−1.13

* = p < 0.05; ** = p < 0.01.

4. Discussion

This study aimed to evaluate the isokinetic performance profiles of knee extensor and flexor muscles in inactive and active individuals, with a particular focus on defining the muscle strength characteristics of sedentary individuals and examining gender differences in these profiles. The results indicated that the absolute values of peak moment, work, and power for the knee extensor and flexor muscles were influenced by gender, with men demonstrating higher performance than women across all physical activity groups. However, when these values were normalized to body weight, the gender-related differences in the extensor muscle group were no longer statistically significant in the inactive and minimally active groups at both testing velocities. Significant differences remained only in the active group. This is the interesting finding from our results, as the level of physical activity increases, the gender-related differences in the relative PM/kg, PW/kg and PPw/kg an extensors and flexors also become more pronounced. To the base of knowledge, consistent with our result, isokinetic muscle strength absolute values of the peak moment, work and power have been previously shown to significantly higher rates in man than the women, for extensor and flexor muscles.^20,21 However, when these values are adjusted relative to body mass, the statistical significance is often diminished.²⁰ However, Pincivero found that these parameters still were statistically significant.²¹ Also, Musselman and Brouwer, 2005 reported that the relative values significantly higher in men than women.²² In the obese subjects found that higher absolute values of the isokinetic values, but still lower relative values of muscle moment than lean subjects.²³ Enoka et al. found the maximal voluntary muscle force or power were fewer declines in women than in men in young people.²⁴ Moreover, one study showed that the absolute and relative knee flexor and extensor isokinetic muscle power evaluated were different in men and women including various training level.²⁵ This study's results are consistent with previous findings. However, our findings provide clearer evidence. Specifically, as the activity level increases, the relative extensor and flexor PM, PW, and PPw values show greater gender differences compared to the inactive condition. Moreover, flexor values are more influenced by angular velocity and gender differences than extensors.

Gender-related differences in muscular performance studies showed that men tend to experience faster fatigue and lower muscular index than women and women showed ore greater fatigue resistance during the isokinetic muscle contraction.²⁰ Also, men show smaller work output decrement and better isometric muscle performance post-fatigue, whereas women recover faster than men after isokinetic exercise at moderate velocities of contraction.²⁶ Avin, also showed that women were more resistant to fatigue than men in elbow, but not in ankle.²⁷ This maybe indicated that gender related of the fatigue resistance depend on the muscle group. Ayala, noticed that the hamstrings reaction time profile was different in the two genders, women had longer total reaction time, pre-motor time and motor time values than men.²⁸ However, we did not measure the fatigue index separately for men and women in our study. Nevertheless, in general, the relative flexor work capacity was higher in men, and sex-related differences were more pronounced in the relative flexor capacity compared to the extensor capacity in this study. One of the studies indicated that relative isokinetic strength and work values had no gender comparison, but the study participants were small and had no information about activity level as well.²⁰ The relative extensor and flexor work capacity, as well as the fatigue index, may show different results between women and men according to activity level. Therefore, a more detailed research is needed to further investigate these differences.

As previously study indicated, both among men and among women, in the parameters of absolute and relative knee isokinetic muscle power, the greatest statistically significant differences were obtained between physically inactive individuals and strength and power athletes in the gender comparison.²⁷ In line with the results of this study, our findings showed that relative power values differed by gender in the active group. However, in the inactive and minimally active groups, the relative extensor PPw/kg values were consistent, as PM/kg and PW/kg were not significantly different in gender comparison.

The majority of studies reported in the literature have not determined the leg muscle strength profiles of inactive or sedentary individuals in men and women as in our study. Only one meta-analysis study with 13,893 participants for adult nonathletic male isokinetic isometric knee extension strength values 1.34–2.23 (knee extension position), 2.92–3.45 (mid-range) and 2.50–3.06 (flexed angle) Nm/kg, while the flexors strength reported 0.85–1.20, 1.15–1.62, and 0.96–1.54 Nm/kg, respectively. In addition, adult nonathletic females obtained less strength to compare with men (1.01–1.50, 2.08–2.74, and 2.04–2.71 Nm/kg, respectively).²⁹ In addition to these findings, our results determined the isokinetic extensor relative PM values of 1.95–2.26 Nm/kg at 60°/s and 1.63–1.83 Nm/kg at 180°/s in both genders for a young inactive population. This differences maybe related the muscle fiber type, Furthermore, muscle contraction characteristics in women are typically characterised by a longer half-relaxation time and lower evoked twitch moment compared to men.^30,31 This attenuation in contractile response aligns with the higher proportion of type I muscle fibers in women,³² which are more involved in moment production throughout the entire range of motion. These fibers, which are adapted for endurance and sustained activity, contribute to the slower contraction and relaxation dynamics observed in females. Sexual dimorphism in muscle fibre type composition probably explains the differences in the relationship between absolute and relative angular velocities between men and women.

Our findings suggest that no significant gender differences exist in knee isokinetic relative extensor peak moment, work and power values among inactive groups. However, as activity levels increase, the gender differences become more pronounced. Additionally, the flexor values exhibited greater variability across genders. Therefore, these findings provide novel insights to the existing literature by highlighting the limited influence of gender on extensor muscle performance among sedentary individuals. Specifically, no significant gender differences were observed in extensor strength parameters such as peak moment (e.g., females = 1.95 ± 0.50 Nm/kg; males = 2.26 ± 0.26 Nm/kg at 60°/s), suggesting that gender-related disparities are minimal in untrained populations. In contrast, flexor strength showed clear and significant gender differences even within the inactive group (e.g., peak moment: females = 0.99 ± 0.24 Nm/kg; males = 1.37 ± 0.32 Nm/kg at 60°/s), indicating a persistent gender-related disparity in hamstring function. As the physical activity level increased, the magnitude of gender differences expanded across all isokinetic variables, especially in the active group. Here, males demonstrated substantially higher relative strength values for both extensors and flexors. For instance, at 60°/s, the peak moment for extensors was 2.39 ± 0.35 Nm/kg in females versus 2.90 ± 0.52 Nm/kg in males, and for flexors, 1.39 ± 0.26 Nm/kg in females versus 1.89 ± 0.43 Nm/kg in males. These trends suggest that training or habitual physical activity amplifies pre-existing gender-based differences in muscle performance, particularly favoring male participants.

Consequently, our results will be a reference for the studies performed with isokinetic dynamometer. Because isokinetic dynomometer has been widely used in scientific and application-based studies since 1968.³³ Since then, isokinetic testing has been widely used in both clinical and athletic populations. The main reasons for the continued use of this method include its high reliability, test safety and the provision of detailed information on joint function and muscle balance.^34,35 Despite the increasing use of field-based assessment methods, isokinetic dynamometry is still considered the gold standard for the quantitative assessment of muscle strength, especially when accurate moment measurement is required. Isokinetic dynamometry is also widely used by clinicians, particularly in the fields of sports medicine and physical therapy, as a tool for assessing and managing musculoskeletal disorders. It plays a key role in both the diagnosis and rehabilitation of various neuromuscular conditions.

Furthermore, In the present study, participants classified as ‘inactive’ according to the IPAQ-SF were interpreted as representative of sedentary individuals. This classification is consistent with previous literature, where low IPAQ-SF scores have been used to identify sedentary behavior patterns.^4,36 The absence of significant gender differences in relative extensor strength values (PM/kg, PW/kg, and PPw/kg) within this group suggests that these parameters may serve as normative reference values for sedentary young adults, regardless of gender. Similar findings have been reported by Douris et al. (2006), who observed minimal gender differences in isokinetic strength among individuals with low physical activity levels.³⁷ As physical activity level increased, however, gender differences became more pronounced in our study, indicating that activity level has a moderating effect on muscle strength, particularly in active populations. These findings underscore the importance of stratifying participants by physical activity level when establishing normative isokinetic strength values and developing gender-specific reference standards.

Although self-report questionnaires such as the IPAQ are valuable tools for assessing physical activity on a large scale, they have limitations. Recall bias, social desirability bias, misinterpretation of questions, individual differences, lack of objective validation, and cultural factors can all contribute to inaccuracies in the data. To overcome these limitations, researchers often recommend combining self-report questionnaires with objective measures such as accelerometry to improve the validity of physical activity data.³⁸ In accordance with this recommendation, in our study, we used the isokinetic dynamometer and assessed isokinetic muscle strength characteristics according to activity level, taking gender into consideration. A similar study was conducted by Miçaoğulları et al. (2016) using this scale in an isokinetic muscle strength study, but the study was conducted on a smaller group of Turkish amateur athletes.³⁹ As a result of the study, has found differences in peak moment values in groups divided into active and inactive groups. Similarly, in this study, we tested the range of muscle strength according to activity level on a larger population by using this IPAQ and isokinteic dynomometer together. This also constitutes the limitation of the study. Additionally, our study has several limitations. First, the sample size was relatively small, which may limit the generalizability of the findings. Second, isokinetic testing was performed only on the right leg, which may not account for possible asymmetries or differences in limb dominance. Future studies should consider larger, more diverse populations and include bilateral measurements to enhance the robustness and applicability of the results. Longitudinal research is also recommended to explore how changes in physical activity level over time may influence isokinetic strength profiles.

5. Conclusion

The present findings provide an additional reference for the evaluation and interpretation of muscle strength characteristics in both active and inactive young women and men. Specifically, one can expect a normalized dominant side extensor strength of around twice the bodyweight in both women and men.

Footnotes

Acknowledgements

The authors would like to thank Prof. Dr. Khalid Rahman, School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University for editing language of the manuscript.

ORCID iD

Sedef Nizam

Ethical considerations

The study has been approved by Balıkesir University Health Sciences Non-Interventional Research Ethics Committee on October 12, 2021 (No: 2021/16) and all participants have signed an informed consent form.

Author contributions

Study plan: Zekine Punduk

Performance of work: Sedef Nizam and Zekine Punduk.

Interpretation or analysis of data: Sedef Nizam and Zekine Punduk

Preparation of the manuscript: Zekine Punduk.

Revision for important intellectual content: Sedef Nizam and Zekine Punduk.

Supervısıon: Zekine Punduk.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors report no funding. Sedef Nizam received a scholarship from TUBITAK-2210/A during this study.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Declaration

This manuscript is derived from the author's master's dissertation, titled “Determination of sedentary concept according to muscle strength structure and characteristics”, completed at “Balıkesir University” in 2023.

References

Tremblay

Aubert

Barnes

, et al. Sedentary behavior research network (SBRN) – terminology consensus project process and outcome. Int J Behav Nutr Phys Act 2017; 14: 1–17.

Matthews

Chen

Freedson

, et al. Amount of time spent in sedentary behaviors in the United States, 2003–2004. Am J Epidemiol 2008; 167(7): 875–881.

Lee

Macfarlane

Lam

, et al. Validity of the international physical activity questionnaire short form (IPAQ-SF): a systematic review. Int J Behav Nutr Phys Act 2011; 8: 1–11.

Craig

Marshall

Sjostrom

, et al. International physical activity questionnaire: 12-country reliability and validity. Med Sci Sports Exerc 2003; 35(8): 1381–1395.

Wolin

Heil

Askew

, et al. Validation of the international physical activity questionnaire-short among blacks. J Phys Act Health 2008; 5(5): 746–760.

Kurtze

Rangul

Hustvedt

. Reliability and validity of the international physical activity questionnaire in the Nord-Trondelag Health Study (HUNT) population of men. BMC Med Res Methodol 2008; 8: 1–9.

Fogelholm

Malmberg

Suni

, et al. International physical activity questionnaire: validity against fitness. Med Sci Sports Exerc 2006; 38(4): 753–760.

Papathanasiou

Georgoudis

Georgakopoulos

, et al. Criterion-related validity of the short international physical activity questionnaire against exercise capacity in young adults. Eur J Cardiovasc Prev Rehabil 2010; 17(4): 380–386.

Silva-Batista

Urso

Lima Silva

, et al. Associations between fitness tests and the international physical activity questionnaire-short form in healthy men. J Strength Cond Res 2013; 27(12): 3481–3487.

10.

Meskers

CGM

Reijnierse

Numans

, et al. Association of handgrip strength and muscle mass with dependency in (instrumental) activities of daily living in hospitalized older adults: the EMPOWER study. J Nutr Health Aging 2019; 23(3): 232–238.

11.

Hannon

Wang-Price

Garrison

, et al. Normalized hip and knee strength in two age groups of adolescent female soccer players. J Strength Cond Res 2022; 36(1): 207–211.

12.

McKay

Baldwin

Ferreira

, et al. Normative reference values for strength and flexibility of 1,000 children and adults. Neurology 2017; 88(1): 36–43.

13.

Pereira

Neri

SGR

Vainshelboim

, et al. Normative values of knee extensor isokinetic strength for older women and implications for physical function. J Geriatr Phys Ther 2019; 42(4): E25–E31.

14.

Risberg

Steffen

Nilstad

, et al. Normative quadriceps and hamstring muscle strength values for female, healthy, elite handball and football players. J Strength Cond Res 2018; 32(8): 2314–2323.

15.

Impellizzeri

Rampinini

Maffiuletti

, et al. Reliability of isokinetic strength imbalance ratios measured using the cybex NORM dynamometer. Clin Physiol Funct Imaging 2007; 27(6): 346–353.

16.

Ayala

De Ste Croix

Sainz de Baranda

, et al. Differences in hamstring flexibility between men and women and the impact of unilateral and bilateral stretching. J Hum Kinet 2012; 31: 59–66.

17.

Saglam

Arikan

Savci

, et al. International physical activity questionnaire: reliability and validity of the Turkish version. Percept Mot Skills 2010; 111(1): 278–284.

18.

Field

. Discovering statistics using IBM SPSS statistics. 4th ed. London: Sage, 2013.

19.

Howell

. Statistical methods for psychology. 7th ed. Belmont: Cengage Learning, 2010.

20.

Borda

Ungur

Irsay

, et al. Sex-related differences in isokinetic muscular contraction. Palestrica of the Third Millennium Civilization & Sport 2014; 15(4).

21.

Pincivero

Gandaio

Ito

. Gender-specific knee extensor torque, flexor torque, and muscle fatigue responses during maximal effort contractions. Eur J Appl Physiol 2003; 89(2): 134–141.

22.

Musselman

Brouwer

. Gender-related differences in physical performance among seniors. J Aging Phys Act 2005; 13(3): 239–253.

23.

Maffiuletti

Jubeau

Munzinger

, et al. Differences in quadriceps muscle strength and fatigue between lean and obese subjects. Eur J Appl Physiol 2007; 101(1): 51–59.

24.

Enoka

Duchateau

. Muscle fatigue: what, why and how it influences muscle function. J Physiol 2008; 586(1): 11–23. Review.

25.

Toskić

Dopsaj

Toskić

, et al. Isokinetic muscle power of the knee extensor and flexor muscles among differently trained people in relation to gender. Hum Mov 2020; 21(3): 81–89.

26.

Gomes

Santos

Correia

, et al. Sex differences in muscle fatigue following isokinetic muscle contractions. Sci Rep 2021; 11(1): 8141.

27.

Avin

Naughton

Ford

, et al. Sex differences in fatigue resistance are muscle group dependent. Med Sci Sports Exerc 2010; 42(10): 1943–1950.

28.

Ayala

De Ste Croix

Sainz de Baranda

, et al. Intersession reliability and sex-related differences in hamstrings total reaction time, pre-motor time, and motor time during eccentric isokinetic contractions in recreational athletes. J Electromyogr Kinesiol 2014; 24(2): 200–206.

29.

Šarabon

Kozinc

Perman

. Establishing reference values for isometric knee extension and flexion strength. Front Physiol 2021; 12: 767941.

30.

Kent-Braun

Doyle

, et al. Human skeletal muscle responses vary with age and gender during fatigue due to incremental isometric exercise. J Appl Physiol 2002; 93(5): 1813–1823.

31.

Wust

Morse

de Haan

, et al. Sex differences in contractile properties and fatigue resistance of human skeletal muscle. Exp Physiol 2008; 93(7): 843–850.

32.

Jeon

, Jhoi J, Kim HJ, Lee H, Lim JY, et al. Sex- and fiber-type-related contractile properties in human single muscle fiber. J Exerc Rehabil 2019; 15(5): 537–545.

33.

Perrine

Edgerton

. Muscle force-velocity and power-velocity relationships under isokinetic loading. Arch Phys Med Rehabil 1968; 49(3): 247–252.

34.

Drouin

Valovich-McLeod

Shultz

, et al. Reliability and validity of the biodex system 3 pro isokinetic dynamometer. Eur J Appl Physiol 2004; 91(1): 22–29.

35.

Impellizzeri

Bizzini

. Isokinetic testing in soccer. In: Clinical practice and sports medicine: soccer injuries. 2009.

36.

Cust

Armstrong

Smith

, et al. Self-reported confidence in recall as a predictor of validity and repeatability of physical activity questionnaire data. Epidemiology 2009; 20(3): 433–441.

37.

Douris

McDonald

Vespi

, et al. Isokinetic and functional strength in sedentary and active males and females. Isokinet Exerc Sci 2006; 14(3): 217–225.

38.

Troiano

Berrigan

Dodd

, et al. Physical activity in the United States measured by accelerometer. Med Sci Sports Exerc 2008; 40(1): 181–188.

39.

Miçooğulları

Yıldızgören

Turhanoğlu

, et al. Amatör sporcularda fiziksel aktivite düzeyleri ile izokinetik kas performansı. Turk J Osteoporos 2016; 22(1): 35–39.

			Age (y)			Height (cm)			Weight (kg)			IPAQ-SF score
Groups		n	Min.	Max.	$\bar{X}$	Min.	Max.	$\bar{X}$	Min.	Max.	$\bar{X}$	Min.	Max.	$\bar{X}$
Inactive	Female	15	20	23	21.40	154	175	164	45	75	55.54	00	594	214.67
Inactive	Male	12	20	28	22.75	167	183	176.33	60	115	79.70	00	594	162.00
Minimally Active	Female	12	20	23	20.66	157	180	168.66	49	80	62.65	780	2772	1557.76
Minimally Active	Male	15	20	25	21.50	167	186	175.14	58	93	75.40	676	2950	1902.42
Active	Female	15	18	23	20.93	157	178	167.06	48	77	58.40	3012	13,500	6328.66
Active	Male	15	20	28	22.13	171	200	184.13	68	109	85.66	3177	6657	4555.86