The effects of lower extremity muscle strength characteristics on grab and track start performance in young competitive swimmers

Abstract

BACKGROUND:

Limited data exist regarding segmental contributions of lower extremity muscles to the swim start performance during different start techniques in young swimmers.

OBJECTIVE:

To determine the differences in the kinematic parameters between the grab start (GS) and track start (TS) techniques and assess the interactions between the lower limb muscle strength and swim start performance.

METHODS:

A total of 40 swimmers, 20 girls (age: 13.70 $\pm$ 1.80 y, height: 161.65 $\pm$ 8.28 cm, body weight: 53.70 $\pm$ 8.65 kg) and 20 boys (age: 13.90 $\pm$ 1.45 y, height: 160.95 $\pm$ 12.70 cm, body weight: 52.95 $\pm$ 12.64 kg), 13–16 y of age, at the competitive level were recruited. Ankle, hip, and knee muscles were tested isokinetically at 60 ${}^{\circ}$ /s and the tests were spread over 24 h to avoid fatigue. Several elements relating to GS and TS were measured using a motion pick-up video camera.

RESULTS:

The angle of entry (EA) at water and knee joint angle (KA) were significantly greater during GS both for boys (EA: 44.18 $\pm$ 1.07 ${}^{\circ}$ vs. 43.03 $\pm$ 1.28 ${}^{\circ}$ ; KA: 112.10 $\pm$ 15.25 ${}^{\circ}$ vs. 107.21 $\pm$ 21.13 ${}^{\circ})$ and girls (45.09 $\pm$ 1.28 ${}^{\circ}$ vs. 43.36 $\pm$ 1.55 ${}^{\circ}$ ; KA: 103.08 $\pm$ 11.21 ${}^{\circ}$ vs. 97.45 $\pm$ 19.52 ${}^{\circ}$ , $p<$ 0.05). Flight time (FT), flight distance (FD), KA, and flight velocity (FV) were significantly higher for boys both during GS and TS, whereas EA was significantly lower for boys during GS compared to girls ( $p<$ 0.05). Lower limb strength performance was positively significantly correlated with FT, FD, and FV both during GS and TS ( $p<$ 0.05). Hip muscle strength was inversely correlated with the EA both during GS and TS ( $p<$ 0.05). The combination of the knee, ankle, and hip extensor and flexor muscle strengths had a greater effect during GS (35% vs. 29%) in RT, (48% vs. 46%) in FT, (59% vs. 57%) in FD, and (63% vs. 57%) in FV compared to the TS.

CONCLUSIONS:

Incorporating lower body strength training into the swimming training schedule may improve swim start performance variables during grab start and track start techniques.

Keywords

Swimming grab and track start neuromuscular strength hip knee ankle

1. Introduction

Start, strokes, and turns comprise the most important technical domains of swimming. Despite the general recognition of the importance given to stroke techniques during swimming, an effective start is essential for success in swimming [1, 2]. The time observed between the start signal and the moment when the swimmer’s head reaches 10 m or 15 m is defined as start performance and it takes up an increasing proportion of the total duration of the competition during short-distancing races [3, 4, 5].

The grab start (GS) and track start (TS) are common techniques in swimming races and most swimmers tend to use one of the two start techniques [6]. In terms of biomechanical aspects, these two start techniques differ distinctively from each other while neither of the two has been strongly linked to total swimming performance [7]. When analyzing the GS technique, both feet of the swimmers are positioned at the front of the block, and hands grab the front edge of the block, inside or outside of both feet. On the other hand, in TS, swimmers place one foot at the front edge of the block while the other foot is placed on the back of the block, with similar hand placement [8].

Considering the determinants that impact swimming performance, the muscular performance of the lower body is one of the most important components of start performance while improved muscle strength comprises an essential role for enhanced sports performance [9, 10]. During both starts, the hips, knees, and ankles extend forcefully in an attempt to maximize horizontal velocity during takeoff. Limited data to date indicate that the hip muscles are the most important contributor to the work done during GS and TS. However, in addition to the hip muscles, the knee and ankle moments have also been shown to generate almost simultaneously for a superior start performance. Both start techniques have also been shown to be dependent on variations in the starting posture, jump or dive directions, different limb-segment interactions, and muscle-recruitment patterns [11]. Considering the differences in starting mechanisms between GS and TS, the contribution of the lower extremity muscles to the start performance might be different due to the positioning of the body during both start techniques. In addition to the contribution of neuromuscular components to the GS and TS performance, a superior start also requires a fast reaction time, significant jumping power, a high take-off velocity, and a decrease in drag force during entry [5]. Since enhanced lower body strength has a significant role in fast starts, the performance of lower extremity muscles i.e., hip, knee, and ankle, may be important in reducing the starting time and, consequently, the overall race time. In this regard, the interaction between lower extremity muscles and start performance may directly affect the ability to exert force on the block during the push-off phase, affecting the take-off velocity and flight distance [12, 13].

Due to the limited number of studies on lower limb muscle strength in relation to a swimming start performance, the aims of this study were (1) to determine the differences in the kinematic parameters between the GS and TS and the possible differences in the two start techniques between the genders, and (2) to assess the interactions between lower limb muscle strength and the performance of the two start techniques.

2. Methods

2.1 Study participants

A total of forty swimmers (13.80 $\pm$ 1.62 y) at the competitive level volunteered to participate in this study. The GPower (3.1.9.2) program was used to determine the sample size. The effect size was determined as $d=$ 2.55 (Type I error (Alpha) 0.05 and Type II error (Beta) 0.20), and the sample size was calculated as at least three individuals for each group. All participants were informed about the equipment and familiarized with the experimental procedures before they underwent testing sessions. Written informed consent was provided by all participants prior to participating in the study approved by the Mersin University Institutional Review Board (Protocol number 281, date of approval: 27.09.2017) in compliance with the ethical standards of the Helsinki Declaration.

The inclusion criteria applied in the research were healthy, physically active (e.g. at least three times a week) boy and girl swimmers aged between 13 and 16 y, who were not suffering from any kind of acute or chronic disease that would limit their ability to participate in the study. Refusal to consent, acute joint pain, treatment for major knee problems within the previous six months such as ligament reconstruction or meniscus tearing, failure to adhere to testing requirements, and/or, evidence of altered training/fitness resulted in exclusion from the study. The swimmers, who met the inclusion criteria were given more information about the purpose of the study and were asked to participate. The participants underwent body composition measures, isokinetic testing measures of the knee, ankle, and hip muscles, and biomechanical evaluation of GS and TS on a separate day with 24 hours of rest between tests to avoid neuromuscular fatigue.

2.2 Bodily measurements

The body composition parameters of participants were expressed as Mean $\pm$ SD. The anthropometric parameters were assessed using Bioelectrical impedance analysis (Tanita 418-MA Japan) prior to isokinetic test sessions. The stature of the participants was measured with a stadiometer in the standing position (Holtain Ltd., UK).

2.3 Evaluation of lower extremity muscle strength

A Cybex NORM (Humac, CA, USA) isokinetic dynamometer was used for the assessment of isokinetic knee extension and flexion peak moment, the participants were seated in the upright position with the hips flexed at an angle of 90 ${}^{\circ}$ . To maintain stabilization during isokinetic testing, the hips and thighs were stabilized using pelvic and thigh straps. For familiarization with the device, the participants performed a series of 10 submaximal reciprocal repetitions (about 50% of MCV), at 180 ${}^{\circ}$ /s before testing. Following the warm-up session, each participant performed five maximal bilateral knee extension (con) and flexion (con) repetitions at 60 ${}^{\circ}$ /s. The participants were asked to perform as quickly as possible and at a maximal effort. They were also told to grasp the handles at the sides of the chair throughout the warm-up and the test. Gravity correction was implemented prior to the isokinetic test protocol session. The participants underwent the same protocol for both legs during all isokinetic testing sessions.

In the following test session, isokinetic testing of the ankle plantar flexor (PF) and dorsiflexor (DF) was performed at 60 ${}^{\circ}$ /s in the supine position. Additional straps were used to stabilize the participant during ankle testing. Ankle ROM was determined as the participant’s maximum PF and DF. After the joint-specific warm-up and two minutes of rest, the participants performed five maximal concentric PF repetitions at 60 ${}^{\circ}$ /s. The participants were told to relax at the end of each repetition and the ankle was returned to the starting position. The same protocol was followed by five concentric maximal DF repetitions at 60 ${}^{\circ}$ /s.

On the third visit to the laboratory, hip extensor and flexor muscle strength was evaluated in a supine position at 60 ${}^{\circ}$ /s. The tested hip was at 0 ${}^{\circ}$ of flexion, with 90 ${}^{\circ}$ of knee flexion, and secured into a brace. The tested thigh was strapped to the dynamometer pad at the femur level. The non-tested thigh was stabilized to the dynamometer chair at 0 ${}^{\circ}$ of hip flexion. For each participant, the evaluation was performed with a joint amplitude of 90 ${}^{\circ}$ (from 10 ${}^{\circ}$ of hip extension to 80 ${}^{\circ}$ of flexion) concentric mode. Upon completion of five sub-maximal contractions, each participant performed five maximal contractions of the hip extensor and flexor muscles at a velocity of 60 ${}^{\circ}$ /s. The pelvis and trunk were strapped to the dynamometer chair to prevent undesirable movements throughout the test. Gravitational corrections were made prior to all test sessions to avoid the effect of limb weight on moment production.

2.4 Video analysis

The swimmers were recorded in groups of two persons. Upon completion of each start technique, each swimmer relaxed during a 50 m swim. The second swimmer was recorded for the first type of start, and when the first swimmer was resting. The same procedure was followed for the remaining swimmers. However, if a swimmer’s arms, legs, or trunk were not fully extended at water entry subsequent to each start, the starts were excluded from further analysis. An automatically generated start signal with a random duration between ‘take your marks’ and the start signal in order to mimic race conditions was applied. Each swimmer performed a standardized 15-minute warm-up consisting of a general easy swim before the testing. Two measurements were executed on the sample of 40 swimmers. Each swimmer made two starts for each type of start, for a total of four starts, and the best times for each start technique were analyzed. A Basler 602f brand video camera with a speed of 100 Hz (capable of taking 100 frames per second) was used to record each start technique for further analysis. One lateral video camera was placed five meters from the edge of the pool and was used to videotape the block and flight phases. The camera was placed 90 ${}^{\circ}$ to the block in the sagittal plane and each swimmer was equipped with 8 passive markers on foot, ankle, knee, hip, shoulder, elbow, wrist, and finger on the right side of their bodies. The videos were used to measure the entry angle, knee angle, flight time, flight distance, flight velocity, and reaction time and determine the angles between the swimmers’ segments axes and the horizontal plane. All output data derived from the video cameras were fed into a computer-assisted motion analysis system (Kinovea 0.8.15) to digitize the data for both GS and TS techniques.

Table 1
Anthropometric characteristics of the swimmers

	Boys ( $n=$ 20)	Girls ( $n=$ 20)
Variables	(Mean $\pm$ SD)	(Mean $\pm$ SD)
Age, years	13.90 $\pm$ 1.81	13.70 $\pm$ 1.45
Body weight, kg	52.95 $\pm$ 12.64	53.70 $\pm$ 8.65
Height, cm	160.95 $\pm$ 12.70	161.65 $\pm$ 8.29
Lean body weight, kg	46.56 $\pm$ 12.17	40.49 $\pm$ 5.84
Percent body fat, %	19.53 $\pm$ 7.01	23.94 $\pm$ 5.02

Note: (mean $\pm$ SD).

Table 2

Differences between the grab and track start for male and female swimmers (mean $\pm$ SD)

	Males ( $n=$ 20)			Females ( $n=$ 20)
Variable	Grab start	Track start	$p$	Grab start	Track start	$p$
Flight time (s)	0.40 $\pm$ 0.03	0.39 $\pm$ 0.03	0.14	0.33 $\pm$ 0.07	0.32 $\pm$ 0.07	0.53
Flight distance (m)	3.05 $\pm$ 0.22	3.00 $\pm$ 0.23	0.43	2.37 $\pm$ 0.28	2.33 $\pm$ 0.28	0.60
Flight velocity (m/s)	6.97 $\pm$ 0.63	6.72 $\pm$ 0.62	0.20	6.34 $\pm$ 0.70	6.16 $\pm$ 0.67	0.42
Entry angle (degree)	44.18 $\pm$ 1.07 ${}^{*}$	43.03 $\pm$ 1.28	0.00	45.09 $\pm$ 1.28 ${}^{*}$	43.36 $\pm$ 1.55	0.00
Knee angle (degree)	112.10 $\pm$ 15.25 ${}^{*}$	107.21 $\pm$ 21.13	0.03	103.08 $\pm$ 11.21 ${}^{*}$	97.45 $\pm$ 19.52	0.04
Reaction time (s)	0.58 $\pm$ 0.30	0.61 $\pm$ 0.29	0.76	0.72 $\pm$ 0.31	0.72 $\pm$ 0.31	0.98

Note: ${}^{*}$ statistically significant, $p<$ 0.05.

Table 3

Differences between male and female swimmers for both start techniques (mean $\pm$ SD)

	Males vs. females			Males vs. females
Variable	Grab start	Grab start	$p$	Track start	Track start	$p$
Flight time (s)	0.40 $\pm$ 0.03 ${}^{**}$	0.33 $\pm$ 0.07	0.00	0.39 $\pm$ 0.03 ${}^{**}$	0.31 $\pm$ 0.07	0.00
Flight distance (m)	3.05 $\pm$ 0.22 ${}^{**}$	2.37 $\pm$ 0.28	0.00	3.00 $\pm$ 0.23 ${}^{**}$	2.33 $\pm$ 0.28	0.00
Flight velocity (m/s)	6.97 $\pm$ 0.63 ${}^{*}$	6.34 $\pm$ 0.70	0.01	6.72 $\pm$ 0.62 ${}^{*}$	6.16 $\pm$ 0.67	0.01
Entry angle (degree)	44.18 $\pm$ 1.07 ${}^{*}$	45.09 $\pm$ 1.28	0.02	43.03 $\pm$ 1.28	43.36 $\pm$ 1.55	0.48
Knee angle (degree)	112.10 $\pm$ 15.25 ${}^{**}$	103.08 $\pm$ 11.21	0.00	107.21 $\pm$ 21.13 ${}^{**}$	97.45 $\pm$ 19.52	0.00
Reaction time (s)	0.58 $\pm$ 0.30	0.72 $\pm$ 0.31	0.23	0.61 $\pm$ 0.29	0.72 $\pm$ 0.31	0.14

Note: ${}^{*}$ statistically significant, $p<$ 0.05, ${}^{**}$ statistically significant, $p<$ 0.000.

The measures of video analysis consisted of flight distance (FD), flight time (FT), flight velocity (FV), the entry angle (EA) and knee angle (KA), and reaction time (RT): For assessment of FD parameters of the participants, the distance covered by the swimmer from the block until his/her hand enters the water was measured and expressed in meters. Block time was determined as the sum of the swimmers’ reaction time and the time to push the exit platform, from the exit signal to the moment the feet leave the exit block. The time between leaving the block and the first contact of the swimmer’s hand with the water was determined as FT, and output data was expressed in seconds. FV was calculated using an indirect measurement calculated from the distance phase and flight phase with the equation FV $=$ FD/FT and expressed in meters per second. To determine the differences between both start techniques, EA was measured using the angle between the horizontal axis and the body while it was quantified at head entry, i.e. angle between the horizontal axis, the head, and the hip, and expressed in degrees. The angle of the knee at block (KA) is the knee joint angle at the moment of the last contact of the foot with the starting block. The time between the starting signal and the moment when the swimmer’s feet leave the block was determined as RT to analyze the interactions between start performance and neuromuscular components, and output data expressed in seconds.

2.5 Statistical analysis

The normality of the data distribution was tested with Shapiro-Wilk test. The results were presented as the Mean $\pm$ SD. A paired-sample $t$ -test was used to analyze within-group comparisons while intra-group comparisons were performed using independent sample $t$ -test analysis. Pearson product-moment correlation coefficient analysis was performed to test potential interactions between neuromuscular strength components and GS and TS performance variables. Linear regression analysis was applied to determine the percentage of variation in GS and TS variables explained by hip, knee, and ankle muscle strength parameters. The variables for the final models were selected based on statistical significance, maximum $R^{2}$ values, and distribution of residuals. The level of statistical significance was set at $p<$ 0.05 and $p<$ 0.001 for all comparisons. GraphPad Software GraphPad Prism 6 was used for graphical expression.

Table 4
Differences between the neuromuscular performance of male and female swimmers

Variable	Right	Left	$p$	Right	Left	$p$
	Males ( $n=$ 20)			Females ( $n=$ 20)
Knee extension (Nm)	166.80 $\pm$ 72.94	169.00 $\pm$ 68.79	0.71	153.80 $\pm$ 30.66	153.85 $\pm$ 33.01	0.99
Knee flexion (Nm)	93.75 $\pm$ 41.14	88.90 $\pm$ 33.75 ${}^{*}$	0.09	76.95 $\pm$ 19.65	75.20 $\pm$ 15.90	0.29
Hip extension (Nm)	182.95 $\pm$ 72.50	176.00 $\pm$ 71.90	0.43	177.70 $\pm$ 37.51	174.60 $\pm$ 38.33	0.24
Hip flexion (Nm)	105.60 $\pm$ 45.54	105.05 $\pm$ 45.54	0.92	102.60 $\pm$ 22.09	99.35 $\pm$ 20.88	0.28
Dorsiflexion (Nm)	90.29 $\pm$ 48.82	81.57 $\pm$ 35.83	0.46	78.75 $\pm$ 26.25	68.85 $\pm$ 33.65	0.04 ${}^{*}$
Plantar flexion (Nm)	24.81 $\pm$ 9.60	25.29 $\pm$ 11.21	0.36	24.45 $\pm$ 9.87	23.70 $\pm$ 7.93	0.67

Note: (mean $\pm$ SD), ${}^{*}$ statistically significant, $p<$ 0.05.

Table 5

The associations between neuromuscular strength and grab start performance

	KE		KF		HE		HF		DF		PF
Variable	Right	Left	Right	Left	Right	Left	Right	Left	Right	Left	Right	Left
FT (s)	0.51 ${}^{**}$	0.50 ${}^{**}$	0.56 ${}^{**}$	0.49 ${}^{**}$	0.48 ${}^{**}$	0.50 ${}^{**}$	0.41 ${}^{**}$	0.41 ${}^{**}$	–	0.39 ${}^{*}$	0.66 ${}^{***}$	0.55 ${}^{***}$
	(0.001)	(0.001)	(0.001)	(0.001)	(0.002)	(0.001)	(0.009)	(0.009)	–	(0.012)	(0.000)	(0.000)
FD (m)	0.35 ${}^{*}$	–	0.42 ${}^{**}$	0.36 ${}^{*}$	–	–	–	–	0.49 ${}^{**}$	0.34 ${}^{*}$	–	0.38 ${}^{*}$
	(0.025)	–	(0.007)	(0.022)	–	–	–	–	(0.001)	(0.031)	–	(0.016)
FV (m/s)	0.43 ${}^{**}$	0.47 ${}^{**}$	0.47 ${}^{**}$	0.37 ${}^{*}$	0.46 ${}^{**}$	0.49 ${}^{**}$	0.39 ${}^{*}$	0.40 ${}^{*}$	–	0.34 ${}^{*}$	–	0.38 ${}^{*}$
	(0.005)	(0.003)	(0.002)	(0.021)	(0.003)	(0.001)	(0.013)	(0.012)	–	(0.031)	–	(0.016)

Note: FT: flight time, FD: flight distance, FV: flight velocity, KE: knee extension, KF: knee flexion, HE: hip extension, HF: hip flexion, DF: dorsiflexion, PF: plantar flexion. ${}^{*}$ Statistically significant, $p<$ 0.05, ${}^{**}$ statistically significant, $p<$ 0.001, ${}^{***}$ statistically significant, $p<$ 0.000.

Table 6

The associations between neuromuscular strength and track start performance

	KE		KF		HE		HF		DF		PF
Variable	Right	Left	Right	Left	Right	Left	Right	Left	Right	Left	Right	Left
FT (s)	0.49 ${}^{**}$	0.47 ${}^{**}$	0.53 ${}^{**}$	0.51 ${}^{**}$	0.46 ${}^{**}$	0.48 ${}^{**}$	0.40 ${}^{*}$	0.40 ${}^{*}$	–	0.38 ${}^{*}$	0.63 ${}^{***}$	0.55 ${}^{***}$
	(0.001)	(0.002)	(0.001)	(0.001)	(0.003)	(0.002)	(0.010)	(0.011)	–	(0.016)	(0.000)	(0.000)
FD (m)	0.41 ${}^{*}$	0.41 ${}^{**}$	0.52 ${}^{**}$	0.49 ${}^{**}$	0.46 ${}^{**}$	0.48 ${}^{**}$	0.40 ${}^{*}$	0.40 ${}^{*}$	–	0.38 ${}^{*}$	0.63 ${}^{***}$	0.55 ${}^{**}$
	(0.028)	(0.009)	(0.001)	(0.001)	(0.003)	(0.002)	(0.010)	(0.011)	–	(0.016)	(0.000)	(0.001)
FV (m/s)	0.52 ${}^{**}$	0.55 ${}^{**}$	0.59 ${}^{**}$	0.51 ${}^{**}$	0.50 ${}^{**}$	0.57 ${}^{**}$	0.51 ${}^{**}$	0.53 ${}^{**}$	–	0.50 ${}^{**}$	0.61 ${}^{***}$	0.51 ${}^{*}$
	(0.001)	(0.001)	(0.001)	(0.001)	(0.001)	(0.001)	(0.001)	(0.001)	–	(0.003)	(0.000)	(0.001)

3. Results

Table 1 shows the means and standard deviations of swimmers’ age, height, body weight, lean body mass, and percent fat mass.

Significant differences were revealed in the GS entrance angle both for boys (44.18 $\pm$ 1.07 vs. 43.03 $\pm$ 1.28 degree) and girls (45.09 $\pm$ 1.28 vs. 43.36 $\pm$ 1.55 degree) compared to the TS entrance angle (Table 2).

The FT, FD, and FV, KA at water entry were significantly higher for boy swimmers both during GS and TS while EA was significantly lower for boy swimmers during GS compared to girl swimmers (Table 3).

The comparison of neuromuscular components revealed that knee flexion parameters were greater in the dominant limb for boy swimmers while dorsiflexion parameters were higher in the dominant limb for girl swimmers (Table 4).

The results of the Pearson moment correlation coefficient analysis revealed positive significant correlations between the neuromuscular components and FT, FD, and FV both during GS (Table 5) and TS (Table 6) performance.

Figure 1.

The correlations between the entry angle during grab start and (a) hip and (b) knee extension and flexion parameters.

Figure 2.

The correlations between the entry angle during track start and (a) hip and (b) knee extension and flexion parameters.

Pearson moment correlation coefficient analysis also showed negative significant correlations between EA during GS and hip (Fig. 1a) and knee (Fig. 1b) extension and flexion parameters and significant negative correlations between EA during TS and hip (Fig. 2a) and knee (Fig. 2b) extension and flexion parameters.

Linear regression analysis was performed to determine the percentage of variation in GS and TS variables explained by hip, knee, and ankle muscle strength parameters. The combination of lower extremity muscle strength (i.e., knee, hip, ankle) explained about 63% of the variation in FV, 59% in FD, 48% in FT, and 35% in RT during GS performance. Similarly, 57% of the total variance in FV, 57% in FD, 46% in FT, and 29% in RT during the TS performance were explained by the combination of strength of these muscle groups.

4. Discussion

The muscular strengths and proper alignments of ankle, knee, and hip muscles in the GS and TS can help swimmers boost their acceleration and momentum off the block and allow them to perform an efficient take-off start. Nevertheless, limited information exists concerning the interactions between lower extremity muscle strength and GS and TS in young competitive swimmers. The current study revealed that the variables of kinematic analysis were not statistically significant for either gender, except for EA during GS (Table 2). The speed, distance, and duration associated with take-off were significantly higher for boys with either start technique. Boy swimmers had significantly lower EA during GS compared to girls. These results indicate that the boy swimmers achieved better start performance for each start technique than the girl swimmers. Significant shorter FT was verified for girl swimmers in previous research while they reported similar FD, FT, and FV despite greater values for boy swimmers [14]. Another study noted that swimmers had greater means (mean) for FT in GS compared with TS. Whereas the difference was not statistically significant both prior to and following the experimental program. The difference in the FT was 0.02 s prior to and 0.01 s following the experimental treatment [8]. Also, the difference in the FT was 0.10 s between these two starting techniques whereas the results were not statistically significant [15]. The difference in the FT was 0.01 s higher during GS for either gender in the current study compared with TS (Table 4). Similar results concerning FT, FD, and FV were also verified in previous studies [1, 16, 17, 18, 19].

Based on kinematic analysis of swim start performance, EA was significantly higher during GS for either gender, whereas it was significantly lower for boys during GS compared to girls. Data from previous studies support these findings where it was proposed that swimmers could practice and perform the appropriate start into the water under the appropriate angle for both start techniques [16, 20, 21]. However, negative significant correlations between EA and hip and knee muscle strength during GS (Fig. 1a and 1b) and TS (Fig. 2a and 2b) show that strength discrepancies of these muscles may be responsible for the decreased EA during either technique due to the loss of horizontal velocity and increase in propulsive efficiency during the transition stage.

In addition to the variations in EA, the angle of the knee joint at water entry was also significantly greater during GS compared to TS for each gender (Table 2). Higher values of knee joint angle during water entry have been shown to produce a greater vertical force during push-off with a rear angle of 100 ${}^{\circ}$ –110 ${}^{\circ}$ compared to a knee angle of 80 ${}^{\circ}$ –90 ${}^{\circ}$ [17]. These results show that a higher knee angle followed by high horizontal take-off and entrance velocity in the x-direction may enhance a steeper water entry and allow swimmers to travel further in the air due to the controlled inertial characteristics of body moment in the sagittal plane. Achieving a high take-off velocity followed by a decreased drag force during entry may enhance a low resistance streamline position during underwater gliding. These kinematic differences can assist swimmers in a superior start and help them to minimize their loss of horizontal velocity and increase propulsive efficiency during the transition stage. However, the occurrence of strength discrepancies in these muscles may cause a poor start due to an improper alignment of the orbit of the center of mass to the horizontal level during take-off and the entrance angle of the center of mass when contacting the water. In this regard, to optimize the maximum efficiency during these swim starts, swimmers and coaches need to consider the neuromuscular performance to find the preferred start technique. In addition to the interactions that occurred in the aforementioned components in the current study, previous research has also demonstrated a significant correlation between measures of lower body power and starting performance in swimmers [22, 23, 24]. Due to the limited number of the study that examined the interactions between neuromuscular performance and GS and TS techniques, it has been shown that lower body strength is a key determinant of starting performance in sprinting [9, 25]. Strong negative correlations between leg strength and swim performance found in these studies, especially for short distances show that the maximal strength parameters of the lower extremities are good predictors of performance in sprint swimming [26, 27, 28, 29]. On the other hand, due to the interactions between the kinematic and neuromuscular components during swimming, it has been emphasized that if the swimmers have a large asymmetry in force and/or strength production or strength discrepancy they should practice and use the TS with the dominant force-producing leg forward. In the absence of these discrepancies, it has been shown that they could specialize in the chosen start and try to improve the weakest points in their technique [30].

However, the comparison of neuromuscular components revealed that knee flexion parameters were greater in the dominant limb for boys while DF parameters were found higher in the dominant limb for girls (Table 4). Additionally, due to the positive significant correlations that occurred between the neuromuscular components and FT, FD, and FV both during GS (Table 5) and TS performance (Table 6), the participants needed to increase their knee and ankle muscle strength performance to optimize the start during training and competitions. Similar interactions have also been reported between swim performance to 5 m and leg-extensor power ( $r=$ 0.76) in the previous research [23]. The results indicated that the combination of knee and hip extension and flexion, and PF and DF muscle strength performance had a greater effect during GS (35% vs. 29%) in RT, (48% vs. 46%) in FT, (59% vs. 57%) in FD, and (63% vs. 57%) in FV compared to the TS performance.

These findings suggest that swimmers can regulate the leg amplitude through a strong synergy between these muscles. Enhancing the strength of these muscles may help swimmers minimize the velocity lost at water entry and lead to performance gains both during GS and TS. The increases in strength performance can be attributed to performance gains during swim start, which in turn, enable the swimmers to generate greater force and power during both start techniques due to the link between strength and starting performance. However, there are some limitations of the current study. Our study consisted of participants between the ages of 13–16 years of age and the application of isokinetic testing was limited to concentric muscle contractions and one specific angular velocity. Future research need to be warranted including athletes with high-performance levels, and varying muscle contractions at different angular velocities to explain these confounding relationships.

5. Conclusions

Variables that account for overall GS and TS performance showed no significant difference between the two different start techniques, except for EA. Increasing strength performance of the lower extremity muscles may help swimmers to exert a greater force on the block during the push-off phase during GS and TS and may provide them with an efficient take-off velocity and flight distance during each start technique. In summary, incorporating lower body strength training into swimmers’ training schedules is important in order to improve GS and TS, which may also increase overall performance in sprint swimming.

Author contributions

All authors listed have made substantial, direct, and intellectual contributions to the work and approved it for publication. All authors read and approved the final version of the manuscript.

CONCEPTION: Buse Argun, Nevzat Demirci and Gökhan Umutlu.

PERFORMANCE OF WORK: Buse Argun, Nevzat Demirci and Gökhan Umutlu.

INTERPRETATION OR ANALYSIS OF DATA: Nevzat Demirci and Gökhan Umutlu.

PREPARATION OF THE MANUSCRIPT: Gökhan Umutlu.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Nevzat Demirci and Gökhan Umutlu.

SUPERVISION: Nevzat Demirci and Gökhan Umutlu.

Ethical considerations

All participants were informed about the equipment and familiarized with the experimental procedures before they underwent testing sessions. Written informed consent was provided by all participants prior to participating in the study approved by the Mersin University Institutional Review Board (Protocol number 281, date of approval: 27.09.2017) in compliance with the ethical standards of the Helsinki Declaration.

Funding

The study was funded by the Mersin University Scientific Research Projects Commission (BAP) (2017-2-TP2-2576), (2018-1-TP2-2734).

Footnotes

Acknowledgments

The results of the current study do not constitute an endorsement of the product by the authors or the journal. The authors would also like to thank the participants involved in the study.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Given his role as an Editorial Board Member, Gökhan Umutlu had no involvement nor access to information regarding the peer review of this article.

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The effects of lower extremity muscle strength characteristics on grab and track start performance in young competitive swimmers

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Methods

2.1 Study participants

2.2 Bodily measurements

2.3 Evaluation of lower extremity muscle strength

2.4 Video analysis

Table 1 Anthropometric characteristics of the swimmers

Table 4 Differences between the neuromuscular performance of male and female swimmers

5. Conclusions

Author contributions

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Anthropometric characteristics of the swimmers

Table 4
Differences between the neuromuscular performance of male and female swimmers