The effect of fatigue on strength-power tests for distinguishing elite-level male kickboxers

Abstract

BACKGROUND:

Based on recent research, slight performance differences, particularly dependent on the state of recovery, might be crucial for tournament success among elite-caliber kickboxers.

OBJECTIVE:

This study aims to; a) determine which strength-power tests could discriminate better between elite and top-elite kickboxers and, b) to evaluate changes in testing results between fatigued and well-rested athletes.

METHODS:

Twenty-two international kickboxers (including World and European Champions) volunteered to participate in this study. Nine kickboxers were assigned to the top-elite group and 13 to the elite group based on their highest tournament achievements. Subjects performed the Wingate test (Win) for anaerobic power; countermovement jump (CMJ) and squat jump (SJ) for neuromuscular power; push-ups and pull-ups for strength endurance; squats (SQ) and bench press (BP) for maximal dynamic strength; handgrip, leg, and back strength for isometric strength after full rest, following the fatigue and advanced fatigue protocols.

RESULTS:

Discriminant function analysis correctly classified the groups at 60.5%, 75.3%, and 86.3% in the resting, fatigue, and advanced fatigue protocols, respectively. Furthermore, all strength-power performances have significantly decreased and lactate_peak increased ( $p<$ 0.05) after the fatigue and advanced fatigue protocols in both groups. Significant interaction were also observed in the Win_peak ( $p<$ 0.001, $\eta_{p}^{2}=$ 0.559), Win_mean ( $p=$ 0.009, $\eta_{p}^{2}=$ 0.246), CMJ ( $p=$ 0.010, $\eta_{p}^{2}=$ 0.273), push-ups ( $p<$ 0.001, $\eta_{p}^{2}=$ 0.389), SQ_absolute ( $p=$ 0.001, $\eta_{p}^{2}=$ 0.337), BP_absolute ( $p=$ 0.014, $\eta_{p}^{2}=$ 0.235) and, Lactate_peak ( $p=$ 0.026, $\eta_{p}^{2}=$ 0.220).

CONCLUSION:

Resistance to fatigue may be the key component for distinguishing elite-level athletes. Thus, strength-power tests should be performed following a certain level of fatigue for the elite athletes due to distinguish them more effectively.

Keywords

Kickboxing strength-power tests strength performance performance decrease Wingate

1. Introduction

Performance measurement is one of the most crucial components to monitor and improve the athletic performance, to reduce their deficiencies, to prevent injuries, and ultimately to achieve better competition results [1, 2]. The monitoring of various performance characteristics during the training process of athletes is another crucial component for long-time development [3]. Accurate and timely monitoring ensures that the athlete can prepare more effectively for the competition, and simultaneously providing valuable information to the coach and sports scientist about deficiencies, developments, or risks and ultimately helps to readjust the goals during preparation periods [2, 4]. Performance measurements could be effective for both, individual combat sports (e.g., kickboxing, boxing, wrestling), and team sports (e.g., football, volleyball, basketball).

Kickboxing is one of the most popular combat sports around the world and its popularity increases constantly, witnessed by reaching more than one million participants worldwide [5]. Lately, its popularity gained another official milestone, when the World Associations of the Kickboxing Organizations (WAKO) [6, 7] was fully recognized by the International Olympic Committee (IOC) in 2021.

In kickboxing competitions, two athletes orient striking actions, consisting of kicks and punches or both variously combined, in an effort to be awarded with points or -depending on the discipline- achieve a knockout. Furthermore, defensive actions are used to prevent from getting hit [8]. Based on these aims, a high-level of technical, and tactical skills, as well as lower and upper body strength, anaerobic power (For high-intensity attacks), aerobic capacity (For faster recovery between the attacks or fights), and speed are required in all of the different competition disciplines (Point fighting, kick light, full contact etc.) [5, 9, 10].

Today, even tiny performance differences can greatly condition the levels’ success of athletes. For example, in the 2020 Tokyo Olympics, Marcell Jacobs won the Olympic Champion title with a time of 9.80 seconds in the athletics 100 meters final race. Meanwhile, Su Bingtian finished the race in 6th place, while arriving only 0.18 seconds later [6]. Similar evidence is shown by Hoelbling et al. [18] linking slight kinematic motion differences in kicking ability to both subjective performance evaluation (Of 10 highly qualified coaches) and overall tournament success [11, 12, 13]. To increase the overall performance of combat sports athletes, endurance and resistance to fatigue occupy an important place [14]. Therefore, proper and planned performance monitoring can contribute to the success of athletes since even very small performance scores can change the results of the competitions [14].

To date, some selected tests have been applied to kickboxers to determine their level of success or monitoring the performance status of them [5, 15]. For example, 1 repetition maximum (RM) bench press or squat tests for maximal dynamic strength [16], countermovement jump (CMJ) or squat jump for neuromuscular power [15], push-up or pull-up for strength endurance [5], Wingate test for anaerobic power and capacity [8] and maximum oxygen uptake (VO_2max) test for the aerobic capacity [5] tests have been performed. All the aforementioned tests have been usually performed in the classical methods (in the rest). However, a question arises as to how these tests will precisely measure the performance scores of the kickboxers when they are performed after exhaustive exercises, as kickboxers may have to play multiple matches during the day [7], and top-elite athletes must maintain their performance both at the end of the match and in the repeated competitions. Therefore, the present study aimed: a) to determine which strength-power tests could discriminate better to elite and top-elite kickboxers as well as, b) to evaluate changes in testing results between fatigued and well-rested athletes.

Table 1
Descriptive characteristics and maximal oxygen consumptions of the participants (Values are mean $\pm$ SD; $n=$ 22)

	Top-elite	Elite	$p$	ES
Age (years)	24.3 $\pm$ 2.5	22.5 $\pm$ 3.1	0.170	0.64, moderate
Training age (years)	13.7 $\pm$ 3.6	11.6 $\pm$ 1.9	0.128	0.73, moderate
Height (cm)	175.5 $\pm$ 4.6	175.9 $\pm$ 5.4	0.871	0.08, trivial
Body mass (kg)	70.0 $\pm$ 7.4	68.3 $\pm$ 5.9	0.564	0.25, small
Fat (%)	7.7 $\pm$ 5.1	7.9 $\pm$ 4.3	0.906	0.04, trivial
VO_2max (ml.min.kg^{- 1})	55.5 $\pm$ 6.0	54.1 $\pm$ 2.9	0.541	0.30, small

2. Methods

2.1 Participants

Prior to the measurement, the necessary participants number of 16 was calculated, using Cohen’s formula for an expected effect size (ES) of 0.80 powered at 0.80 and using G*Power 3.1 software [17]. A total of 22 national and international male kickboxers (Including one World Champion, one European Champion, three European Cup Champions, two World Cup Champions) voluntarily participated in this study. Nine of them were assigned to the top-elite group (Mean $\pm$ SD: age $=$ 24.3 $\pm$ 2.5 years, height $=$ 175.5 $\pm$ 4.6 cm, body mass $=$ 70.0 $\pm$ 7.4 kg, training experience $=$ 13.7 $\pm$ 3.6 years, fat $=$ 7.7 $\pm$ 5.1%) and 13 to the elite group (Mean $\pm$ SD: age $=$ 22.5 $\pm$ 3.1 years, height $=$ 175.9 $\pm$ 5.4 cm, body mass $=$ 68.3 $\pm$ 5.9 kg, training experience $=$ 11.6 $\pm$ 1.9 years, fat $=$ 7.9 $\pm$ 4.3%). All participants are actively competing in national and international tournaments and they have not experienced any extreme-rapid weight losses. The top-elite group was compiled with medalists of World- or European Championships (within the last 3 years). The elite group comprises all other national championship medalists (within the last 3 years), who are actively participating at tournaments. Descriptive characteristics of all participants are presented in the Table 1. Participants, their coaches, and their families were informed about the experimental procedures with a detailed explanation of the aims and risks involved inthe investigation, and written informed consent was obtained. The research protocol was conducted according to the Declaration of Helsinki for human experimentation and was approved by the ethics committee of Ataturk University, Winter Sports and Sport Sciences Institute (Project Number; 2020/22).

Figure 1.

Study design.

2.2 Design

The testing sessions were performed during a national team training camp, 10-12 days after the kickboxing world championships. As shown in Fig. 1, after measurement of certain physical characteristics (described below) and a familiarization session (consisting of performing all tests with submaximal intensity), subjects performed selected strength-power tests for anaerobic power, maximal dynamic strength, isometric strength, muscle power and strength endurance tests after full rest (classic testing). Then the same tests were performed again immediately after two exhaustive exercise protocols (Fatigue and advanced fatigue) to investigate the difference between top-elite and elite kickboxers regarding different levels of acute fatigue. The tests were performed in different sessions and grouped as follows:

Countermovement jump (CMJ), squat jump (SJ), push-up,

Pull-up, squat (SQ), handgrip strength (HGS), and isometric leg strength test,

Bench press (BP), isometric back strength (IBS), Wingate leg anaerobic test.

The tests in same order were repeated after exhaustive exercises for the second and third sections of the study (i.e., Fatigue and advanced fatigue). In the rest, 3-5 min rest period was used between the tests. In the fatigue and advanced fatigue protocols, 30 sec rest period was used between the tests. The tests were completed in random order in the first section, whereas the previous order was followed in the other protocols. All performance measurements for each of the participants were completed on 10 different days in total (see Fig. 1). All the tests were performed in the same time of day (i.e., between 10:00 and 12:00 AM) to avoid any diurnal variation of the performance. Participants followed the same dietary plans arranged by their dietician during the study protocol. Moreover, participants were not allowed to perform any exhaustive activity 48 hours before the testing day and use any supplements during this period. All tests were conducted in a controlled laboratory environment (steady 20-22^∘C aired conditioned room, 38-40% air humidity) and all participants were verbally encouraged in all three sections of tests (Rest, fatigue, and advanced fatigue) to maximize their performance.

2.3 Procedures

2.3.1 Anthropometric characteristics

The height [cm] of the participants was measured with a portable stadiometer (Holtain Ltd., Crosswell, Crymych, Dyfed, United Kingdom). The body mass (BM [kg]), relative [%] and absolute [kg] fat mass and relative [%] and absolute [kg] fat free-mass (FFM) were estimated using air displacement plethysmography via the Body Composition Tracking System Analysis (BOD POD, COSMED Inc, Concord, California, USA). Before each test, the BOD POD device was calibrated according to the manufacturer’s instructions using a 2-point calibration. Before testing, athletes were instructed to wear a sports beret, tight-fitting shorts, and a swimming cap. Also, all participants were instructed to remove all metal, including jewelry and watches. BM was measured to the nearest 0.01 kg using the system’s calibrated scale. All kickboxers were instructed to sit in the chamber, breathe normally, and to avoid any physical movement. A minimum of 2 trials were performed. If measurements were not within 150 ml of each other, a third trial was conducted. Thoracic gas volume was estimated using BOD POD software, which uses standard prediction equations and has demonstrated no difference compared with measured lung volumes [18].

2.3.2 Maximum oxygen consumption (VO_2max) test

VO_2max levels (ml.kg^{- 1}.min^{- 1}) were measured using a portable gas-exchange system via face mask and turbine system in breath-by-breath mode via SN7-COSMED K5 (Rome, Italy). Gas analyzers for oxygen (O ${}_{2})$ and carbon dioxide (CO ${}_{2})$ were calibrated for every test with a specific gas concentration (O₂ 16.10% and CO₂ 5.20% and NO₂ rest) and the turbine volume transducer with a 3-liter calibration syringe, according to the manufacturer’s recommendations.

The exercise was conducted following Bruce protocol [19] with a professional treadmill (h/p/cosmos Saturn 250-125r, sports and medical gmbh 83365, Nußdorf-Traunstein/Germany). The test was started on a 10% gradient at 2.7 km.h^{- 1}. The incline and speed were increased every 3-minutes. The test ended after maximum exhaustion by the athlete.

2.3.3 Anaerobic power and capacity test

Wingate test has been used to determine the anaerobic power and capacity on a Monark cycle ergometer (Ergomedic 894E, Vansbro, Sweden). For the full-rest protocol, the participants started with a 5-7 min warm-up at a self-selected submaximal cycling workload or load-free. After 1 min of rest, subjects then completed a specific warm-up consisting of 3-min of cycle exercise at 120W (60rpm) with a 3-5 s sprint completed at the end of each minute. After 2-min of rest, the Wingate test was carried out. The test consisted of 30s maximal cycling, launched with the pedals stationary (Initial speed was zero), and the load was set at 10% of the participant’s body mass with the resistance on the flywheel [8]. Participants were instructed to: a) start the first pedal stroke with the dominant leg; b) reach the maximum rpm in the shortest time possible; and c) provide a maximal effort to maintain this pedaling speed until the end of the test. Strong verbal encouragement to complete a maximal effort was provided to all participants. Power output was recorded during each second of the test. The following variables were calculated: peak power (Win_peak), mean power for the test duration (Win_mean).

The peak blood lactate concentration of the participants was determined from a drop of capillary blood sample (0.5 $\mu$ l) taken from the fingertip of the hand, with a portable 80-g hand analyzer (Lactate Scout+, SensLab GmbH, Leipzig, Germany) capable of measuring with the electroenzymatic method in approximately 15 seconds. A lancet and lancet gun (Vital Plus, China) were used to collect blood samples. The lactate samples were obtained 1, 3, 5, 7 and 9 (if necessary) min after the Wingate tests to see the peak value.

2.3.4 Maximal dynamic strength tests

1 repetition maximum (1RM) Bench press (BP) and squat (SQ) tests were conducted to measure the maximal dynamic strength of the kickboxers [5]. For the 1RM BP test, the participants were assisted with lift-off to a start position, with the arms fully extended above the chest. The tests began with the subject lowering the bar until it touched the chest. Then the athletes pushed the bar upward until reaching full extension position. For trials to be considered valid, a) they had to be carried out at the full defined range of motion and return to the starting position, b) perform the test without chest bounce, foot movement, or the gluteus maximus leaving the bench. Participants performed individual warm-up protocols and were allowed to select the amount of weight they would attempt to lift for the 1RM BP. 1RM for the parallel back squat was determined for each participant using the protocol described by Baechle et al. [20]. A lift was counted valid if the top of the thighs were parallel to the ground during the lowest point of the descent (observed visually) and the bar continued to move upward throughout the ascent, without assistance. Two to three spotters were present during each SQ and BP attempt. A standard 20 kg Olympic barbell and Olympic disks (Ivanko, Reno, Nevada) were used during the tests. The athletes performed 3 trials of each test at 3-5 minutes’ intervals. The load was increased by 3-10% in successful trials or reduced by 3-10% in unsuccessful trials according to the request of the participant. There was no limitation on how many attempts they had during these tests.

2.3.5 Isometric strength tests

Hand grip strength (HGS), (Takei A5001 Hand Grip Dynamometer, Tokyo, Japan) and Leg & Back strength (Takei A5002 Leg Dynamometer, Tokyo, Japan) dynamometers was selected to measure isometric strength [8]. Participants performed an individual warm-up session prior the tests. Then, the dynamometer was adjusted to participants’ hand size, by ensuring that the second joint of the index finger was bent with a 90^∘ angle at the handle. Participants were asked to maximally squeeze the dynamometer, using only the dominant hand with a straight arm. According to the manufacturer guidelines, trials were limited to three with maximum effort and the best score was recorded as valid.

During the Isometric leg strength (ILS) test, participants wore training shoes and stood on the foot-plate of the Takei dynamometer with the pelvis positioned flat against a wall. Athletes flexed the legs, sliding down the wall until an extension angle of 135^∘. Participants then reached down with fully extended elbows so the pull-bar of the dynamometer could be placed in their hands and the chain length adjusted individually for each participant. Participants were instructed to pull the bar by extend their legs with maximal effort but without ‘jerking’ [21]. The highest score of three attempts was used for further analysis.

At the Isometric back strength (IBS) test, participants were instructed to stand on the foot-plate of the Takei dynamometer similar to the ILS test. This time, the participant has straightened legs and arms and performs a flexion in the hip joints until touching the patella with the tips of the index fingers [21]. Then, the pull-bar of the Takei dynamometer was placed in the hands and the chain length was adjusted to each participant. A reverse grip was adopted for the measurement to prevent the use of shoulder muscles during the ‘pull motion’. Subjects were also instructed to keep their head up during measurement. The highest score of three attempts was used for further analysis.

2.3.6 Neuromuscular power tests

Countermovement jump (CMJ) and squat jump (SJ) tests were selected to assess the neuromuscular power of the lower extremities [14]. After an individual warm-up session, the participants were positioned in an upright position in the center of the Optojump optical bars (Microgate, Bolzano, Italy). The device synchronized and arranged according to the manufacturer’s recommendations for each vertical jump. During the stance, their feet were shoulder-width apart and their toes pointed forward.

For the CMJ, subjects started from the upright standing position with their hands on their hips (without arm swing). hey were then instructed to flex their knees ( $\sim$ 90^∘) as quickly as possible and jump maximally in the ensuing concentric phase [22]. To assess the SJ, subjects started from the upright standing position with their hands on their hips. And then, they were instructed to flex their knees and wait for a predetermined knee position ( $\sim$ 90^∘) for 3 s, followed by an explosive jump to maximum altitude.

2.3.7 Strength endurance tests

Push-up and pull-up tests were chosen to determine the strength endurance of the kickboxers [5, 14, 23]. All tests were performed on Martial Arts “tatami” mats. Before the tests, the participants carried out self-selected warm-ups including calisthenic and dynamic stretching exercises. Push-ups were performed from a front leaning rest position. Hands were placed nearly shoulder-width apart, and feet up to 0.3 m apart according to each participants’ shoulder-width. During the tests, the participants maintained a fixed body position from the ankles to the shoulders. The motion started with complete arm extension, while the end of the motion occurred when the chest was lowered to the floor without contact. The maximum number of repetitions performed continuously (Without stopping in any of the stages of the test), using full range of motion were defined as valid score.

During the pull-up test, participants grasped an overhead horizontal bar (distance between hands was slightly greater than shoulder-width), pronated (palms opposite of body trajectory) handgrip while hanging vertically. Full range of motion was defined from an extended arm position to an elbow joint flexion, enabling the participant to lift the chin above the bar. Swinging or twisting motions were avoided during the trial [24].

2.3.8 Exhaustive exercise protocols (fatigue and advanced fatigue)

For the fatigue and advanced fatigue preparations, standardized protocols were used to reduce interindividual differences due to technique expertise. For this purpose, the specific kickboxing circuit training protocol (SKCTP [25]) was chosen, as it reflect the actual time duration of official kickboxing competitions. This protocol had been applied using pad work training by a highly ranked expert coach. After the SKCTP, all participants performed 15rep x 3set burpees with 30sec rest interval with the maximum speed to create extra fatigue on both lower and upper limbs. For the advanced fatigue protocol, all athletes performed a second block of the fatigue protocol, explained above.

2.4 Statistical analysis

Further statistical analyses were performed using SPSS 25 (IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY, USA). Significant level was defined as $\alpha=$ 0.05. Descriptive statistics were calculated and the results are presented as mean $\pm$ standard deviation. The normal distribution of data was verified using the Shapiro-Wilk test.

Independent sample t-test was used to determine whether there were significant differences between the top-elite and elite group. Cohen’s d formula [26] was calculated as post-hoc tests to determine the effect size. Results were classified according to Hopkins [27] ( $<$ 0.2 $=$ trivial (T); 0.20-0.59 $=$ small (S); 0.60-1.19 $=$ moderate (M); 1.20-1.99 $=$ large (L); 2.00-3.99 $=$ very large (VL); and $\geqslant$ 4 $=$ nearly perfect (NP)).

Repeated measures two-way ANOVA was used to determine the fatigue effect on the measurements and interaction between the groups (Groups [top-elite and elite] * protocols [rest, fatigue and advanced fatigue]). Partial eta square ( $\eta_{p}^{2}$ ) was calculated as post-hoc test to establish effect size.

Additionally, a discriminant function analysis was used to determine which test and protocol most accurately distinguished elite and top-elite kickboxers. The collinearity of data was analyzed to identify correlations among the test scores for rest, fatigue, and advanced fatigue protocols. The discriminant function analysis model was separately used for each test scores and each protocol. The structural coefficient was used to determine the variables that discriminate between elite and top-elite. A structural coefficient above .30 was considered as relevant for the interpretation of the linear vectors [15].

3. Results

There was no significant difference in the descriptive characteristics and VO_2max between the groups according to the independent sample t-test and, the effect sizes of the variables were between trivial to moderate ( $p>$ 0.05 for all comparisons, ES; from 0.04 to 0.73).

Table 2
Comparisons of strength-power variables obtained after different protocols

	Rest	Fatigue	Advanced fatigue	ES (d) respectively
Win_peak (W $\cdot$ kg^{- 1})
Elite	13.1 $\pm$ 0.7	9.4 $\pm$ 0.5	7.3 $\pm$ 0.5	0.43 (S), 2.06 (VL), 2.29 (VL)^{†,λ,a, b,c}
Top-elite	13.4 $\pm$ 0.6	10.5 $\pm$ 0.4	8.8 $\pm$ 0.8
Win_mean (W $\cdot$ kg^{- 1})
Elite	7.4 $\pm$ 0.5	5.0 $\pm$ 0.3	3.8 $\pm$ 0.5	1.44 (L), 2.97 (VL), 3.08 (VL)^{†,λ,a, b,c}
Top-elite	8.1 $\pm$ 0.4	6.4 $\pm$ 0.5	5.3 $\pm$ 0.4
Lactate_peak (mmol/L)
Elite	13.2 $\pm$ 1.5	16.3 $\pm$ 1.7	20.0 $\pm$ 2.2	$-$ 0.80 (M), $-$ 0.79 (M), $-$ 1.67 (L)^{†,λ, a,b, c}
Top-elite	12.2 $\pm$ 0.8	15.0 $\pm$ 1.4	17.0 $\pm$ 1.3
CMJ (cm)
Elite	38.0 $\pm$ 6.1	25.8 $\pm$ 4.2	16.6 $\pm$ 3.2	0.25 (S), 1.0 (M), 1.95 (L)^†,a,b,c
Top-elite	39.3 $\pm$ 5.0	29.9 $\pm$ 3.8	22.1 $\pm$ 2.3
SJ (cm)
Elite	31.6 $\pm$ 4.7	20.6 $\pm$ 2.8	12.5 $\pm$ 1.3	0.37 (S), 1.14 (M), 2.73 (VL)^{λ, a,b, c}
Top-elite	33.2 $\pm$ 4.0	23.4 $\pm$ 2.1	16.3 $\pm$ 1.4
Push-up (rep)
Elite	67.8 $\pm$ 8.3	50.5 $\pm$ 7.8	30.0 $\pm$ 4.8	0.60 (M), 1.22 (L), 2.82 (VL)^{†,λ,a,b ,c}
Top-elite	72.0 $\pm$ 5.1	58.0 $\pm$ 3.7	41.1 $\pm$ 2.7
Pull-up (rep)
Elite	21.3 $\pm$ 2.6	12.7 $\pm$ 1.6	7.3 $\pm$ 1.0	0.53 (S), 1.38 (L), 3.24 (VL)^{λ,a, b , c}
Top-elite	24.1 $\pm$ 7.0	17.3 $\pm$ 4.4	13.1 $\pm$ 2.3
SQ_relative (kg^{- 1})
Elite	1.92 $\pm$ 0.16	1.47 $\pm$ 0.11	1.00 $\pm$ 0.08	0.15 (T), 0.91 (M), 1.57 (L)^{†,a, b, c}
Top-elite	1.94 $\pm$ 0.13	1.57 $\pm$ 0.10	1.12 $\pm$ 0.08
SQ_absolute (kg)
Elite	131.0 $\pm$ 7.8	100.5 $\pm$ 5.4	67.6 $\pm$ 4.2	0.67 (M), 1.89 (L), 2.75 (VL)^{†,λ, a, b, c}
Top-elite	135.5 $\pm$ 5.3	109.8 $\pm$ 4.3	78.0 $\pm$ 3.2
BP_relative (kg^{- 1})
Elite	1.37 $\pm$ 0.14	1.09 $\pm$ 0.11	0.72 $\pm$ 0.07	0.06 (T), 0.73 (M), 1.94 (L)^{†, a, b, c}
Top-elite	1.38 $\pm$ 0.12	1.16 $\pm$ 0.08	0.84 $\pm$ 0.05
BP_absolute (kg)
Elite	93.6 $\pm$ 10.3	74.6 $\pm$ 7.8	48.9 $\pm$ 5.3	0.26 (S), 0.79 (M), 1.64 (L)^{†, a, b , c}
Top-elite	96.6 $\pm$ 12.3	81.6 $\pm$ 9.9	59.3 $\pm$ 7.2
HGS_relative (kg^{- 1})
Elite	0.74 $\pm$ 0.07	0.57 $\pm$ 0.04	0.49 $\pm$ 0.04	0.11 (T), 0.77 (M), 0.38 (S)^{a,b, c}
Top-elite	0.75 $\pm$ 0.07	0.61 $\pm$ 0.04	0.51 $\pm$ 0.05
HGS_absolute (kg)
Elite	51.0 $\pm$ 6.6	39.5 $\pm$ 3.8	33.6 $\pm$ 1.5	0.26 (S), 0.85 (M), 0.88 (M)^{a, b , c}
Top-elite	52.7 $\pm$ 6.0	42.7 $\pm$ 3.7	35.8 $\pm$ 3.2
IBS_relative (kg^{- 1})
Elite	2.11 $\pm$ 0.17	1.89 $\pm$ 0.14	1.48 $\pm$ 0.14	0.07 (T), 0.23 (S), 0,41 (S)^{a, b, c}
Top-elite	2.12 $\pm$ 0.21	1.93 $\pm$ 0.19	1.54 $\pm$ 0.15
IBS_absolute (kg)
Elite	144.0 $\pm$ 11.2	129.1 $\pm$ 8.0	100.6 $\pm$ 8.7	0.31 (S), 0.49 (S), 0.71 (M)^{a,b, c}
Top-elite	148.5 $\pm$ 16.8	135.1 $\pm$ 15.3	107.2 $\pm$ 9.7
ILS_relative kg^{- 1})
Elite	2.76 $\pm$ 0.24	2.53 $\pm$ 0.21	1.89 $\pm$ 0.15	0.19 (T), 0.34 (S), 0.48 (S)^{a, b, c}
Top-elite	2.84 $\pm$ 0.22	2.56 $\pm$ 0.18	2.10 $\pm$ 0.16
ILS_absolute (kg)
Elite	188.0 $\pm$ 10.8	172.5 $\pm$ 9.2	170.2 $\pm$ 11.3	0.57 (S), 0.72 (M), 1.05 (M)^{a, b, c}
Top-elite	197.8 $\pm$ 16.1	178.8 $\pm$ 15.2	180.9 $\pm$ 14.5

Note: The values are presented as mean $\pm$ SD, ES: Effect Size, HGS: Hand Grip Strength, IBS: Isometric Back Strength, ILS: Isometric Leg Strength, CMJ: Counter Movement Jump, SJ: Squat Jump, SQ: Squat Strength, BP: Bench Press Strength, Win_peak: Wingate peak power, Win_mean: Wingate mean power T: Trivial ES, S: Small ES, M: Moderate ES, L: Large ES, VL: Very Large ES. ^†: Significant interaction between groups in the fatigue protocols (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^aFatigue protocol significantly different from Rest protocol ( $p<$ 0.05), ^bAdvanced Fatigue protocol significantly different from Rest protocol ( $p<$ 0.05), ^cAdvanced Fatigue protocol significantly different from the Fatigue protocol ( $p<$ 0.05).

Figure 2.

Graphical display for the anaerobic power of the top-elite and elite kickboxers. Note: Ft: Fatigue Protocol; Ad. Ft.; Advanced Fatigue Protocol, $\eta_{p}^{2}$ : Partial eta squared. ^†Significant interaction between groups in fatigue and advanced fatigue protocol (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^*: Significantly different from Rest protocol ( $p<$ 0.05), ^#: Significantly different from Fatigue protocol ( $p<$ 0.05).

Figure 3.

Graphical display for the neuromuscular power of the top-elite and elite kickboxers. Note: Ft: Fatigue Protocol; Ad. Ft.; Advanced Fatigue Protocol, $\eta_{p}^{2}$ : Partial eta squared. ^†Significant interaction between groups in fatigue and advanced fatigue protocol (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^*: Significantly different from Rest protocol ( $p<$ 0.05), ^#: Significantly different from Fatigue protocol ( $p<$ 0.05).

Figure 4.

Graphical display for the strength endurance of the top-elite and elite kickboxers. Note: Ft: Fatigue Protocol; Ad. Ft.; Advanced Fatigue Protocol, $\eta_{p}^{2}$ : Partial eta squared. ^†Significant interaction between groups in fatigue and advanced fatigue protocol (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^*Significantly different from Rest protocol ( $p<$ 0.05), ^#: Significantly different from Fatigue protocol ( $p<$ 0.05).

Figure 5.

Graphical display for the maximal dynamic strength of the top-elite and elite kickboxers. Note: Ft: Fatigue Protocol; Ad. Ft.; Advanced Fatigue Protocol, $\eta_{p}^{2}$ : Partial eta squared. ^†Significant interaction between groups in fatigue and advanced fatigue protocol (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^*: Significantly different from Rest protocol ( $p<$ 0.05), ^#: Significantly different from Fatigue protocol ( $p<$ 0.05).

Figure 6.

Graphical display for the isometric strength of the top-elite and elite kickboxers. Note: Ft: Fatigue Protocol; Ad. Ft.; Advanced Fatigue Protocol, $\eta_{p}^{2}$ : Partial eta squared. ^†Significant interaction between groups in fatigue and advanced fatigue protocol (time * group). $\lambda$ : Significant difference between the groups (top-elite - elite) ( $p<$ 0.05). ^*: Significantly different from Rest protocol ( $p<$ 0.05), ^#: Significantly different from Fatigue protocol ( $p<$ 0.05).

All strength-power variables decreased, and lactate_peak increased significantly ( $p<$ 0.05) after the fatigue and advanced fatigue protocols in both top-elite and elite groups as described by “a, b, c” in Table 2 and “*^#” in Figs 2 to 5.

In all the performance variables below, the performance of elite athletes decreased significantly more than top-elite athletes after fatigue and advanced fatigue protocols. On the other hand, in the elite athletes, lactate_peak increased significantly more than top-elite athletes. Thus, there were significant interaction (group*protocols) in the:

Win_peak; (F ${}_{(1.2,25.3)}=$ 25.369, $p<$ 0.001, $\eta_{p}^{2}=$ 0.559, Table 2 and Fig. 2 Panel A), Win_mean; (F ${}_{(1.4,28.2)}=$ 6.515, $p=$ 0.009, $\eta_{p}^{2}=$ 0.246, Table 2 and Fig. 2 Panel B), CMJ; (F ${}_{(1.1,22,3)}=$ 7.493, $p=$ 0.010, $\eta_{p}^{2}=$ 0.273, Table 2 and Fig. 3 Panel A), push-up; (F ${}_{(2,40)}=$ 12.723, $p<$ 0.001, $\eta_{p}^{2}=$ 0.389 Table 2 and Fig. 4 Panel A), SQ_relative (F ${}_{(1.2,25.4)}=$ 8.479, $p=$ 0.005, $\eta_{p}^{2}=$ 0.298 Table 2), SQ_absolute; F ${}_{(1.4,29.5)}=$ 10.148, $p=$ 0.001, $\eta_{p}^{2}=$ 0.337, Table 2 and Fig. 5 Panel A), BP_relative; (F ${}_{(1.3,26.2)}=$ 8.599, $p=$ 0.004, $\eta_{p}^{2}=$ 0.301 Table 2), BP_absolute; F ${}_{(1.3,26)}=$ 6.154, $p=$ 0.014, $\eta_{p}^{2}=$ 0.235, Table 2 and Fig. 5 Panel B) and, Lactate_peak; (F ${}_{(1,20.7)}=$ 5.650, $p=$ 0.026, $\eta_{p}^{2}=$ 0.220 Table 2).

Top-elite and elite kickboxers distinguished by 60.5% in the rest protocol, 75.3% in the fatigue protocol and 86.3% in the advanced fatigue protocol according to the discriminant function analysis Moreover, Win_mean power was the test with the highest discriminant score among the other strength-power tests.

4. Discussion

In the present study, aerobic fitness and strength-power variables of elite and top-elite level kickboxers under different fatigue conditions were compared. Moreover, we investigated which strength-power performance test separately and which protocol (Resting period, after fatigue and advanced fatigue) distinguished effectively the groups totally.

The findings indicate that both groups were able to perform similarly at the tests after resting period, however, their performance differences increased as the level of fatigue increased. There were significant interactions between the groups in the Win_peak power, Win_mean power, CMJ, push-up, SQ and BP (Relative and absolute for both) and lactate_peak variables. Additionally, the discriminant scores between the groups were 60.5% for the resting period, 75.3% for the fatigue 86.3% advanced fatigue protocols. Among all tests, Win_mean power has the most successful discrimination scores relating to the average values of the three protocols (77.3%, 95.5% and 95.5% respectively).

Table 3
Discriminant scores (%) of the original grouped cases classification

Discriminant scores (%)
	Rest	Fatigue	Advanced fatigue
Win_peak (W.kg^{- 1})	54.5	86.4	90.9
Win_mean (W.kg^{- 1})	77.3^*	95.5^*	95.5
Win_Lactatepeak	63.6	77.3	81.8
CMJ (cm)	59.1	63.6	86.4
SJ (cm)	54.5	77.3	95.5
Push-ups (rep)	63.6	72.7	90.9
Pull-up (rep)	63.6	77.3	100^*
SQ_absolute (kg)	59.1	81.8	90.9
BP_absolute (kg)	50.0	68.2	86.4
HGS_absolute (kg)	59.1	72.7	72.7
IBS_absolute (kg)	63.6	68.2	72.7
ILS_absolute (kg)	59.1	63.6	72.7
TOTAL	60.5	75.3	86.3

Note: HGS: Hand Grip Strength, IBS: Isometric Back Strength, ILS: Isometric Leg Strength, CMJ: Counter Movement Jump, SJ: Squat Jump, SQ: Squat Strength, BP: Bench Press Strength, Win: Wingate, *: Highest discriminant score of each protocol.

In general, strength-power parameters of athletes are measured and evaluated in resting conditions. Thus, there is limited study regarding fatigue effect on strength-power characteristics of the elite kickboxers. However, in a previous study using a similar study design with male wrestlers, Özbay and Ulupınar [27] compared some strength-power parameters on 13 top-elite and 13 elite wrestlers after rest and exhaustive exercise [14]. Significant differences were only found between the groups in the mean relative leg power and arm power tests. Yet, when the same tests were carried out after exhaustive exercise, significant differences in relative arm peak power, absolute and relative mean power, BP, SQ, HGS, ILS tests were detected. Moreover, the discriminant scores of the groups in resting and strenuous exercise protocols were 65.4% and 92.3%, respectively. The current research supports previous research [14] regarding top-elite athletes who were able to maintain their performance better than elite level athletes. This situation is likely the reason for their success, as combat sports demand not only high levels of physical performance [25, 28] but also the ability to endure the physical and mental stress throughout an entire match [5, 28]. Therefore, the resistance to fatigue not only after but also during the competition is one of the main components for success while physiological recovery might be another key component for maintaining the performance effectively as previously indicated [29, 30, 31, 32]. For example, the effect of active recovery [15 min at 70% of the anaerobic threshold [31] or 10 min. at 50% of maximal aerobic speed [30] on lactate removal or the acid-base balance after simulated combat matches. However, even when tired, faster physiological recovery and high-performance indicators of the kickboxers aiming for success are a necessary feature, and this situation can be overlooked in tests performed in a rested state.

To establish the discriminatory factors that may differentiate winners and losers, Tabben et al. [33] showed that karate winner athletes used more lower-limbs than their defeated counterparts, during the competition. Similarly, Ouergui et al. [34] reported similar results in high level kickboxers with higher frequency of lower-limb techniques (i.e., roundhouse kick). Later, Ouergui et al. (2016) compared the physical, physiological and hormonal responses through simulated full contact kickboxing combats in relation to the match outcome and showed that winners executed more straight punches, total punches, roundhouse kicks, total kicks, and total attacking techniques than losers while all other parameters (e.g., mean and peak powers, CMJ performances) did not differ across winners and defeated athletes [35]. In fact, although winners and losers were compared in the aforementioned studies [33, 34, 35], winners were not necessarily the elite level athletes. This lack of elite status among winners may result in insufficient distinction between the groups based on physiological and physical variables [35]. By combining the results of these three studies, it becomes clear that techniques requiring high levels of anaerobic power, speed, and strength are critical. Therefore, conducting specific power tests after inducing fatigue may be essential to effectively distinguish between kickboxers at different performance levels. This approach can help identify subtle differences in their physical capabilities that are not apparent when they are in a rested state [36]. Confirming this, significant differences for lower-limb anaerobic power were found between the top-elite and elite kickboxers and increased by fatigue level (Rest: Win_mean; 1.44, large effect size; Fatigue: Win_mean; 2.97, very large effect size and advanced fatigue: 3.08, very large effect size). Additionally, in the above-mentioned study, a new kickboxing anaerobic speed test has been developed by Gençoğlu et al. [36]. As a gold standard performance test, the authors used lower-limb anaerobic power (Maximal cycling sprint tests) for comparison between elite and sub-elite kickboxers [36]. They also found significant differences between elite ( $n=$ 18) and sub-elite ( $n=$ 24) kickboxers for lower limb anaerobic power (MCST_single; $p=$ 0.001, ES; 1.20). Correspondingly, the results of the present study showed significant interaction in some lower-limbs performance test between top-elite and elite kickboxers (Win_peak, Win_mean, CMJ; SQ_relative and SQ_absolute.

4.1 Limitations

In the present study, we assessed the physical performance of male only top-elite and elite athletes. The applicability of these results to high-level women kickboxers will have to be separately explored. In addition, we suggest that the mental status of these athletes should be considered in future studies as there are indications that it might affect the results [37].

5. Conclusion

To the best of our knowledge, this study is the most comprehensive study so far, of high-level kickboxers in terms of comparison of performance under different but functional conditions. the same wide range of strength-power parameters in rest and two different fatigue conditions. Considering that even tiny performance differences can greatly affect success of athletes, it is essential to distinguish between high and highest skill levels. This research indicates that establishing high levels of fatigue prior to testing constitutes a valid way to detect these differences, since testing at rest does not unveil the differences.

Funding

This work was supported by Erzurum Technical University, Scientific Research Coordination Unit. Project Number: 2020/22.

Author contributions

Conceptualization: Cebrail Gençoğlu, Süleyman Ulupınar, Serhat Özbay.

Data curation: Cebrail Gençoğlu, Serhat Özbay, Vedat Çınar.

Formal analysis: Serhat, Özbay, Süleyman Ulupınar, Cebrail Gençoğlu.

Methodology: Vedat Çınar, Ibrahim Ouergui, Dominik Hölbling.

Writing - original draft: Süleyman Ulup $\imath$ nar, Cebrail Gençoğlu, Dominik Hölbling.

Writing - review & editing: Ibrahim Ouergui, Dominik Hölbling.

Supplementary data

The supplementary files are available to download from https://dx-doi-org.web.bisu.edu.cn/10.3233/IES-240023.

Supplementary table and Figure

Footnotes

Acknowledgments

This work was supported by XXX University, Scientific Research Coordination Unit. Project Number: 2020/22. Measurements were carried out at XXX University, Sports Sciences Application and Research Center.

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The effect of fatigue on strength-power tests for distinguishing elite-level male kickboxers

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

Table 1 Descriptive characteristics and maximal oxygen consumptions of the participants (Values are mean ± SD; n = 22)

2.1 Participants

2.3 Procedures

2.3.1 Anthropometric characteristics

2.3.2 Maximum oxygen consumption (VO2max) test

2.3.3 Anaerobic power and capacity test

2.3.4 Maximal dynamic strength tests

2.3.5 Isometric strength tests

2.3.6 Neuromuscular power tests

2.3.7 Strength endurance tests

2.3.8 Exhaustive exercise protocols (fatigue and advanced fatigue)

2.4 Statistical analysis

3. Results

Table 2 Comparisons of strength-power variables obtained after different protocols

Table 3 Discriminant scores (%) of the original grouped cases classification

5. Conclusion

Funding

Author contributions

Supplementary data

Supplementary table and Figure

Supplementary table and Figure

Footnotes

Acknowledgments

References

Table 1
Descriptive characteristics and maximal oxygen consumptions of the participants (Values are mean $\pm$ SD; $n=$ 22)

2.3.2 Maximum oxygen consumption (VO_2max) test

Table 2
Comparisons of strength-power variables obtained after different protocols

Table 3
Discriminant scores (%) of the original grouped cases classification