Comparison of the effects of isokinetic and isotonic strength training in team sport athletes: A randomized controlled trial

doi:10.21203/rs.3.rs-2723434/v1

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Research Article

Comparison of the effects of isokinetic and isotonic strength training in team sport athletes: A randomized controlled trial

https://doi.org/10.21203/rs.3.rs-2723434/v1

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Background

Athletes may benefit from isokinetic training (IK) to improve strength and jump performance. However, previous studies comparing IK methods to isotonic resistance training (IT) have utilized high-repetition protocols and a Dynamometer, which are usually reserved for laboratory testing or rehabilitation settings.

Methods

This study compared the effects of IK and IT using ≤ 6 repetitions on strength and jump performance in 50 male, team-sport athletes (ages 18–35) during COVID-19 lockdown using the commercially-available TechnoGym BioCircuit Dynamometer. With statistical significance set to p < 0.05, this 4-group randomized parallel study assessed the effects of an 8-week isokinetic at 80°/s (IK80; n = 16) and 25°/s (IK25; n = 12) or isotonic training program (IT; n = 15) compared to a control group (CG; n = 7) on anthropometric measurements, peak torque at 80°/s (PT80) and 25°/s (PT25), one-repetition maximum (1-RM) leg extension, and countermovement (CMJ) and squat jump height.

Results

BM, FFM, FM, and TC were not different between groups post intervention. Strength increased in IT (PT80: p = 0.006; PT25: p = 0.023; 1-RM: p = 0.001), IK80 (PT80: p = 0.004; PT25: p = 0.021; 1-RM: p = 0.009), and IK25 (PT80: p = 0.042; PT25: p = 0.048; 1-RM: p = 0.009) compared to CG, with no difference between intervention groups (p = 1.000). SJ increased in all intervention groups (IT: +1.5cm, p = 0.036; IK80: +2.7cm, p < 0.001; IK25: +1.9cm, p = 0.021) compared to the CG (CG-IT: p = 0.005; CG-IK80: p = 0.009; CG-IK25: p = 0.004), with difference between groups (all p = 1.000). CMJ improved only in IT (+ 1.4cm, p = 0.035) and IK80 (+ 2.7cm, p < 0.001) with no difference between groups (p = 1.000).

Conclusions

Low-repetition IK and IT can be effectively used to improve strength and jump performance. However, the efficacy of IK on CMJ depends on training velocity and repetition count, with higher velocity training protocols (80°/s) being more effective for jump performance and lower speeds potentially more useful for improving maximal strength (25°/s).

Resistance training

leg extension exercise

soccer

handball

football

Isokinetic training (IK) facilitates production of force at the same speed throughout a movement’s range of motion. Several decades of studies comparing training methodologies have noted that IK allows for maximal effort generation through a muscle’s complete range of motion¹. This method stands in contrast to isotonic loading, which is based on the maximal strength of the weakest joint angle, thus leaving remaining joint angles working inherently submaximally.

A decade ago, IK was utilized almost exclusively for strength and power testing in the sport sciences^2–4, as well as in rehabilitation settings, particularly following anterior cruciate ligament reconstruction^4,5. Hewett et al.² clearly demonstrate that the angular velocity of the isokinetic training form has a major influence on how the muscle is loaded, and research in both athletic⁶ and general¹ populations have demonstrated its effectiveness in increasing strength, power, and hypertrophy⁷. Team sport athletes, such as football, hockey, and handball players, may also benefit from this training style, in contrast to isometrics or isotonics, as it proves beneficial for increasing strength parameters as well as sport-specific performance parameters^1,8. Previous studies on IK methods in athletic populations predominantly utilize a repetition range of 8–12 repetitions, which is known to emphasize hypertrophic adaptions rather than maximal strength⁹.

The Dynamometer, the primary and most widely practiced method of IK and testing, is expensive, can only be used by one athlete at a time, and is therefore more exclusive in its uses until equipment manufacturer TechnoGym SpA (Cesena, Italy) released isokinetic strength training to commercial fitness studios via a new equipment line, BioCircuit. This development gives amateur athletes and the general population gym-goers access to IK, which requires a further investigation of the effectiveness of this training form on non-elite athlete populations and in non-rehabilitation scenarios.

The COVID-19 pandemic, with little-to-no possibilities for school or club sport training, presented a unique challenge for the research team. As the BioCircuit Dynamometer entered local commercial gyms, this offered a more accessible, potentially more efficient training solution for athletes unable to train their sport during lockdown. As mentioned above, previous studies on the effectiveness of IK on various populations have, however, utilized high-repetition or to-failure protocols¹⁰. To the best of our knowledge, there are currently no comparable studies comparing isokinetic and isotonic strength training based on six or fewer repetitions. This study’s aim is to clarify whether or not IK, compared with classic isotonic strength training via the leg extension of the BioCircuit device, is equally or more effective for strength and intramuscular coordination (IK) development at a low repetition count (1–5 reps). Additionally, this work should identify angular velocity-specific differences within isokinetic strength training as well as explore the correlations between training styles and resulting body composition.

Experimental Approach to the Problem

Prior to the start of the study, ethical approval was obtained from the university’s ethics committee in accordance with the Declaration of Helsinki. This study was conducted between December 2020 and February 2021. A 4-group randomized parallel study design was used to assess the effects of an 8-week isokinetic or isotonic resistance training program on anthropometric measures and performance. The independent variables consisted of 3 different training forms (isokinetic training at 80°/s [IK80] and 25°/s [IK25], and isotonic training [IT]. The fourth group was the control group [CG]. Dependent variables were body mass (BM), fat-free mass (FFM), fat mass (FM), body fat percentage (BFP), thigh circumference (TC), peak torque 80°/s (PT80) and 25°/s (PT25), one-repetition maximum (1-RM) leg extension, countermovement (CMJ) and squat jump height (SJ), as well as the eccentric utilization ratio (EUR) and peak power (P_peak) derived from the jumps.

Subjects

Sixty-three healthy male adults (18–35 years) currently playing soccer or team handball were recruited for this study. Eight subjects did not meet medical inclusion criteria and were therefore prevented from participating. All subjects were informed about the benefits, risks, methods and procedures used in this study. The 55 volunteers who agreed to participate gave written informed consent. Seven subjects were randomly assigned to the control group (CG). The remaining participants were assigned to the intervention groups (IK80, IK25, IT) using block randomization via an online random integer generator and random sequence generator. Participants were instructed to maintain their normal diet. During the study, no training of the lower extremities was allowed in addition to the intervention. Five subjects dropped out of the study and were therefore excluded from analysis (personal reasons N = 3; illness N = 1; non-study related injury N = 1). A total of 50 subjects completed this study (see Table 1).

Procedures

Testing and training were done at a local commercial gym at the same time of the day. Each test was performed by the same researcher. Pre-testing took place in the week prior to the intervention. Post-testing was conducted 48 h after the last trainings session. Testing procedures were identical in both sessions.

Anthropometry

Bioelectrical impedance analysis (BIA) (Tanita MC-780MA, Tanita Europe BV, Amsterdam, Netherlands) was used to measure BM, FFM, FM, and BFP with subjects wearing only underwear. Participants were instructed to refrain from alcohol 24h, from physical exercise 12h, and from food or fluid intake 5h prior to measurement. For better reliability, subjects completed a 24-hour dietary recall to maintain their diet at post-testing. In addition, prior to the BIA, participants were asked to visit the bathroom before they had to lie supine on an examination bench for 5 minutes. TC was assessed at the right leg using measuring tape at 15 cm proximal from the base of the patella.

Strength and performance

Before performance testing, participants completed a 5-minute warm-up on a stationary bike, followed by 10 repetitions of dynamic quadriceps stretching. Jumping ability was measured using mobile phone (Sony Xperia X Compact, Sony Group Corporation, Tokyo, Japan) video recordings at 60 frames per second analyzed by the MyJump2 app (version 2.2.1) on a tablet (iPad Air 2, Apple Corporation, Cupertino, United States). MyJump2 is considered a valid and highly reliable tool with a respectable capacity to detect changes in jump height^11,12. Participants were asked to perform 3 submaximal SJ before performing 3 maximal SJ with hands on hips and 30 seconds rest between jumps. For this, subjects had to perform a squat until the hip joint was below the knee joint. Then a three-second countdown began before the subjects jumped as high as possible. For reliability analysis intraclass correlation coefficients (ICC) estimates were calculated based on a mean-rating (k = 2), absolute-agreement, 2-way random-effects model. SJ ICC was 0.963. The best SJ attempt was used for further analysis. From participants’ BM and SJ height P_peak was estimated using the equation suggested by Sayers at al.¹³. The same procedure was used for CMJ with the only difference that countermovement was allowed. CMJ ICC was 0.960. From SJ and CMJ height EUR was calculated¹⁴:

EUR=(CMJ-SJ)/SJ · 100.

Strength was measured using a leg extension machine (Biocircuit Leg Extension, TechnoGym Deutschland GmbH, Neu-Isenburg, Germany) which allows isotonic and isokinetic training. Seat and lever settings were adjusted for each individual and kept identical for all tests. Subjects completed a bilateral warm-up set with 10 repetitions using 30 kg. Subsequently, all strength tests were performed unilaterally on the right side because the resistance required for bilateral testing could not be selected on the machine. No verbal encouragement was given during testing, and participant’s buttocks and back had to have contact with the seat throughout each trial. In the isokinetic tests, subjects had to reach maximum knee extension starting from 90° knee three times as forcefully as possible. This was done for both 80°/s (PT80) and 25°/s (PT25) angular velocity with 2 minutes of rest between trials. Peak torque (PT) in kilograms was displayed by the machine for each repetition individually. The highest value of the three tests was used for further analysis. Two minutes after PT25 measurement, 1-RM testing in the leg extension was performed. The first weight attempted was the highest PT value of the isokinetic tests plus 1 kg. If a repetition was successfully completed, weight was increased by 1-5kg until no valid attempt was possible. For failed attempts, the weight was reduced by 1–5 kg, respectively. Between trials, there were 2 minutes of rest. The highest resistance successfully completed was noted for further analysis.

Table 1

Baseline group characteristics: group mean ± standard deviation.
Group	Age (years)	Body weight (kg)	Height (cm)
Control Group (N = 7)	22 ± 3	76.7 ± 7.1	182 ± 4
Isokinetic training 80°/s (N = 16)	24 ± 5	79.6 ± 8.3	182 ± 6
Isokinetic training 25°/s (N = 12)	23 ± 4	80.1 ± 10.0	180 ± 5
Isotonic training (N = 15)	25 ± 6	82.8 ± 12.7	183 ± 7

Resistance training protocol

The training protocol spanned 8 weeks and consisted of 3 sessions per week. Sessions were supervised (researcher-to-participant ratio 1:2) and took place 48-72h apart. Each session started with the warm-up described earlier under performance testing. All groups completed 5 sets of 4 bilateral knee extension repetitions and 3 minutes of rest between sets. The IK80 and IK25 group were instructed to complete repetitions with maximum effort. The starting weight of the IT group was based on the 1-RM pre-testing and increased by 3 kg when 6 repetitions could be completed in the last set. The eccentric phase was performed in a controlled manner and the concentric phase as quickly as possible. Twenty-one of the 24 sessions had to be completed to complete the study.

Statistical Analyses

Statistical analysis was done using Microsoft Excel (version 2108, Microsoft Corporation, Redmond, United States) and IBM SPSS Statistics (version 26, IBM Corporation, Chicago, United States). Data are shown as means ± standard deviations (SD). Statistical significance was set to p < 0.05. Shapiro-Wilk test was used to test for normal distribution and Levene's test was used to test for homogeneity of variance. A two-way analysis of variance (time*group) with repeated measures was performed to determine differences in anthropometric and performance measures. Where necessary, Bonferroni post-hoc analysis was performed. Within-group effect sizes (ES) were calculated using the following formula: mean change score / SD of the mean change score¹⁵. The between-group ES were calculated by subtracting the mean change scores divided by their pooled SD.

All results of anthropometric and performance measurements are summarized in Tables 2 and 3.

Table 2

Pre-, post-test anthropometric measurements, relative change, ES, group by time interactions, group and time effects.
	Group	Pre	Post	Mean change score	ES	Group * time		Group		Time
	Group	Pre	Post	Mean change score	ES	p	\({\eta }_{p}^{2}\)	p	\({\eta }_{p}^{2}\)	p	\({\eta }_{p}^{2}\)
BM [kg]	CG	76.7 ± 7.1	77.5 ± 7.0	0.87	0.47	0.306	0.075	0.658	0.034	0.005**	0.162
	IK80	78.6 ± 8.3	81.0 ± 8.0	1.40	0.60
	IK25	80.1 ± 10.0	81.5 ± 10.9	1.40	0.68
	IT	82.8 ± 12.7	82.8 ± 11.6	0.05	0.02
FFM [kg]	CG	64.0 ± 5.2	64.0 ± 6.1	0.01	0.01	0.409	0.060	0.518	0.048	0.505	0.012
	IK80	65.9 ± 4.6	66.3 ± 4.2	0.46	0.26
	IK25	64.9 ± 5.0	65.4 ± 5.3	0.49	0.29
	IT	67.8 ± 7.7	67.5 ± 7.2	-0.35	-0.31
FM [kg]	CG	12.6 ± 3.9	13.5 ± 3.5	0.86	0.71	0.714	0.029	0.733	0.027	0.001**	0.240
	IK80	13.7 ± 4.3	14.7 ± 4.8	0.94	0.77
	IK25	15.1 ± 6.1	16.1 ± 6.6	0.91	0.78
	IT	14.9 ± 5.9	15.3 ± 5.3	0.41	0.22
BFP [%]	CG	16.3 ± 4.2	17.4 ± 3.9	0.01	0.75	0.703	0.030	0.737	0.027	< 0.001***	0.272
	IK80	16.6 ± 4.2	17.8 ± 4.1	0.01	0.75
	IK25	18.4 ± 4.8	19.2 ± 5.1	0.01	0.59
	IT	17.5 ± 4.3	18.1 ± 4.2	0.01	0.36
TC [cm]	CG	50.3 ± 2.4	51.2 ± 3.0	0.89	0.83	0.446	0.056	0.153	0.107	0.003**	0.166
	IK80	53.8 ± 3.3	54.1 ± 3.4	0.50	0.44
	IK25	53.8 ± 4.5	54.8 ± 4.6	0.97	0.55
	IT	53.6 ± 3.0	53.8 ± 2.5	0.19	0.15
BM = body mass; FFM = fat-free mass; FM = fat mass; BFP = body fat percentage; TC = thigh circumference; CG = control group; IK80 = isokinetic training at 80°/s; IK25 = isokinetic training at 25°/s; IT = isotonic training. p < 0.01; *p < 0.001

Anthropometry

There were no anthropometric differences between groups at baseline. BM increased in IK80 (+ 1.4kg, p = 0.014) and IK25 (+ 1.4kg, p = 0.031), but not in CG (+ 0.9kg, p = 0.296) and IT (+ 0.1kg, p = 0.925). However, BM was not different between groups post intervention (all p = 1.000). There were no FFM changes. FM increased in IK80 (+ 0.9kg, p = 0.010) and IK25 (+ 0.9kg, p = 0.031), but not in CG (+ 0.9kg, p = 0.116) and IT (+ 0.4kg, p = 0.271). However, FM was not different between groups post intervention (all p = 1.000). BFP changed only in IK80 (+ 1.15%, p = 0.003), but not in CG (+ 1.03%, p = 0.069), IT (+ 0.57%, p = 0.140), nor IK25 (+ 0.73%, p = 0.089). However, BFP was not different between groups post intervention (all p = 1.000). TC increased only in IK25 (+ 0.97 cm, p = 0.016), but not in the other groups (CG: +0.87cm, p = 0.087; IT: +0.19cm, p = 0.592; IK80: +0.50cm, p = 0.142). However, IK25 TC was not different post intervention compared to CG (p = 0.208), IT (p = 1.000), and IK80 (p = 1.000).

Table 3

Pre-, post-test performance measurements, relative change, ES, group by time interactions, group and time effects.
	Group	Pre	Post	Mean change score	ES	Group * time		Group		Time
	Group	Pre	Post	Mean change score	ES	p	\({\eta }_{p}^{2}\)	p	\({\eta }_{p}^{2}\)	p	\({\eta }_{p}^{2}\)
PT80 [kg]	CG	49 ± 6	51 ± 5	1.57	0.36	0.045*	0.159	0.081	0.135	< 0.001***	0.599
	IK80	52 ± 8	64 ± 8	12.00	1.36
	IK25	51 ± 8	62 ± 8	10.83	1.18
	IT	55 ± 13	64 ± 9	9.27	1.26
PT25 [kg]	CG	59 ± 9	61 ± 8	2.14	0.43	0.013*	0.208	0.162	0.105	< 0.001***	0.681
	IK80	62 ± 12	79 ± 13	17.50	1.54
	IK25	60 ± 9	78 ± 15	18.25	1.51
	IT	63 ± 15	79 ± 14	16.00	1.48
1-RM [kg]	CG	59 ± 12	59 ± 12	0.57	0.41	0.001**	0.316	0.057	0.149	< 0.001***	0.728
	IK80	64 ± 11	76 ± 8	12.13	1.19
	IK25	62 ± 11	80 ± 12	17.33	2.84
	IT	66 ± 15	80 ± 13	14.07	1.78
CMJ [cm]	CG	31.1 ± 3.6	30.3 ± 3.3	-0.85	-0.41	0.009**	0.219	0.103	0.124	0.017*	0.223
	IK80	33.9 ± 4.9	36.6 ± 4.7	2.74	1.09
	IK25	36.0 ± 7.1	36.3 ± 5.5	0.35	0.15
	IT	35.6 ± 5.8	37.0 ± 3.3	1.36	0.54
SJ [cm]	CG	28.9 ± 3.1	27.3 ± 2.7	-1.60	-0.95	0.013*	0.206	0.037*	0.167	0.009**	0.255
	IK80	31.6 ± 4.6	34.3 ± 4.5	2.67	0.99
	IK25	33.4 ± 6.2	35.3 ± 5.1	1.90	0.54
	IT	33.3 ± 5.8	34.9 ± 4.9	1.54	0.61
EUR	CG	7.8 ± 4.6	11.3 ± 8.9	3.45	0.43	0.091	0.130	0.411	0.060	0.477	0.029
	IK80	7.3 ± 6.0	6.9 ± 4.8	-0.33	-0.05
	IK25	7.9 ± 8.4	3.0 ± 7.2	-4.86	-0.66
	IT	7.4 ± 5.9	6.2 ± 2.1	-1.19	-0.19
P_peak [W]	CG	3170 ± 225	3112 ± 314	-57.56	-0.47	0.023*	0.185	0.018*	0.196	0.001**	0.325
	IK80	3471 ± 395	3697 ± 366	225.22	1.08
	IK25	3598 ± 387	3777 ± 428	178.85	0.65
	IT	3716 ± 564	3812 ± 314	96.18	0.60
PT80 = peak torque 80°/s; PT25 = peak torque 25°/s; 1-RM = one-repetition maximum; CMJ = countermovement jump; SJ = squat jump; EUR = eccentric utilization ratio; P_peak = estimated peak power from the squat jump; CG = control group; IK80 = isokinetic training at 80°/s; IK25 = isokinetic training at 25°/s; IT = isotonic training. p < 0.05; p < 0.01; **p < 0.001

Performance

All results of performance tests are summarized in Table 3. There were no differences in performance between groups at baseline. Strength increased in the IT (PT80: +9.3kg, p < 0.001; PT25: +16.0kg, p < 0.001; 1-RM: +14.1kg, p < 0.001), IK80 (PT80: +12.0kg, p < 0.001; PT25: +17.5kg, p < 0.001; 1-RM: +12.1kg, p < 0.001), and IK25 (PT80: +10.8kg p < 0.001; PT25: +18.3kg p < 0.001; 1-RM: +17.3kg, p < 0.001), but not in the CG (PT80: +1.6kg, p = 0.608; PT25: +2.1kg, p = 0.601; 1-RM: +0.6kg, p = 0.849). Strength post intervention was higher in IT (PT80: p = 0.006; PT25: p = 0.023; 1-RM: p = 0.001), IK80 (PT80: p = 0.004; PT25: p = 0.021; 1-RM: p = 0.009), and IK25 (PT80: p = 0.042; PT25: p = 0.048; 1-RM: p = 0.009) compared to CG, but not different between intervention groups (all p = 1.000). CMJ, SJ, EUR, and P_peak did not change in the CG with p = 0.359, p = 0.133, p = 0.191, p = 0.459, respectively. Significant increments in CMJ height have been seen after training in IT (+ 1.4cm, p = 0.035) and IK80 (+ 2.7cm, p < 0.001) with no difference between these groups (p = 1.000). Following the intervention CMJ was higher in IT (p = 0.025) and IK80 (p = 0.037) compared to the CG, but not the IK25 (IK25-IT: p = 1.000; IK25-IK80: p = 1.000). SJ height changed in all intervention groups (IT: +1.5cm, p = 0.036; IK80: +2.7cm, p < 0.001; IK25: +1.9cm, p = 0.021) and was higher following training compared to the CG (CG-IT: p = 0.005; CG-IK80: p = 0.009; CG-IK25: p = 0.004), but not different between intervention groups (all p = 1.000). EUR did not change in IT (-1.19, p = 0.507) and IK80 (-0.33, p = 0.847). Only in IK25 EUR was lower following training (-4.87, p = 0.018) and lower compared to CG (p = 0.022). P_peak did not change in IT (+ 96W, p = 0.074) but increased in IK80 (+ 225W, p < 0.001) and IK25 (+ 179W, p = 0.004) and was higher following training compared to CG (CG-IT: p = 0.005; CG-IK80: p = 0.025; CG-IK25: p = 0.012) with no difference between IK80 and IK25 (p = 1.000). Standardized differences in the pre to post changes between CG, IK80, IK25, and IT in strength and jumping performance are presented in Fig. 1.

Figure 1: Standardized differences in the pre to post changes between groups per test.

CG = control group; IK80 = isokinetic training at 80°/s; IK25 = isokinetic training at 25°/s; IT = isotonic training; PT80 = isokinetic peak torque at 80°/s; PT25 = isokinetic peak torque at 25°/s; 1-RM = one-repetition maximum; CMJ = countermovement jump; SJ = and squat jump.

Strength and power qualities were not significantly different between the IK and IT groups during pre-testing, and peak torque (PT) improved in all training groups. Athletes in the IK80 group displayed notable increases at 80°/s (+ 23%), as well as 25°/s (+ 27%), followed by the IK25 group in the fast condition (+ 21.6%). However, IK25 overtook the IK80 group in the PT25 post-testing with a 30% increase. These findings are consistent with similar studies, finding that IK training faster speeds can improve high-speed movement, as well as lower-speed strength movements. Coyle and colleagues¹⁶ also noted that training only at a higher velocity of 300°/s improved PT at this speed (+ 18%), as well as increasing PT at a mid-velocity range of 180°/s (+ 17%). Smith & Melton¹⁷ added that high-speed IK training may produce the most results over slow IK and isotonic training due to higher limb speed in sport. However, the ideal training speed to improve PT remains elusive, as speeds of 30°/s and 140°/s were found to increase PT in rowers and canoe racers, although no differences were found at 90°/s¹⁸. Training at 30°/s was found by one study to improve PT at both 30°/s and 270°/s, but participants training at 270°/s experienced PT increases only in their condition, not at a lower speed¹⁹. Although the training velocities of the IK groups in the present study cannot be considered high in comparison to other studies, these results infer that training at a high speed may indeed improve performance at some lower velocities, without direct training.

Transferability of high-speed vs. low-speed IK training must be further considered, as high-speed IK appears complementary to high-speed movements that require rapid muscle contraction speed, such as jumping, while slower-speed IK proved most beneficial for building maximal strength, which is obliged to a slower rate of muscular contraction. Maximal strength within the IK25 group peaked by 29%, followed by the IT (+ 21%) and IK80 (+ 18.8%) conditions. This follows along with findings from previous studies that faster speeds in the IK80 condition may not be optimal for improving 1RM strength due to muscle contraction speeds; rather, isotonic and isometric conditions are more effective for improving 1RM strength²⁰. Still other studies found isotonic squats with free weights to be more efficient in improving squat performance as IK training with higher repetition counts on a machine¹⁰. Kovaleski and colleagues²¹ hypothesized that this differentiation may be due to developing strength over an entire range of motion in isotonic training versus focusing on the concentric phase in the IK condition. Thus, the 1RM improvements in the IK25 group may be due to the reduced repetition count and lower speed, allowing a focus on exerting force during the entire range of motion.

Both IK80 and IT groups demonstrated positive outcomes in the CMJ (+ 8% and + 4% respectively), adding to previous findings that isotonic and high-speed isokinetic training can moderately improve vertical jump performance²². Smith & Melton¹⁷ also noted the gain in vertical and broad jump performance in a high-speed IK group (+ 5.4% at 240°/s) over slow IK and isotonic training (+ 3.9% at 60°/s and + 1.6% respectively). They also uncovered a dramatically improved broad jump performance in the high-speed IK group (+ 9.1%). Other researchers have also confirmed improvements in drop jumps after IK training⁶, adding confirmation that high-speed IK training can vastly improve power qualities. González-Ravé and colleagues⁸ found no significant relationship between isokinetic training and vertical jump performance in elite handballers when training knee flexion and extension at 60°/s and 180°/s, begging the question of whether or not an open-chain training method can consistently transfer to a closed-chain movement and in which phase of the competition year jump testing should take place for most accurate results. Smith & Melton¹⁷ also found no significant benefits of high-speed IK on sprint performance, as the 240°/s group saw no improvement in the 40-yard dash and training at 60°/s boosted sprint performance only by 1.1%. As such, it can be inferred that high-speed IK training, although beneficial for improving high-effort power performance, does not extend these benefits to sprinting performance.

There are several limitations to this paper, due to the context of COVID-19 in 2020 and 2021. No nutritional tracking or intervention was used during the course of the eight weeks, although body composition was measured at the start and end of the study. However, the changes in FM and BFM in the IK80 and IK25 training groups beg the question of whether the increase in strength is due only to isokinetic training methods or also to nutritional factors, such as caloric intake or reduced energy expenditure during lockdown phases. Future studies comparing methods of strength training should include either nutrition tracking, consulting, or an intervention, as well as strive to include female participants and athletes from diverse sporting backgrounds.

For further study and use of isokinetics versus other modalities, the authors recommend use of a dynamometer for isokinetic testing. However, an expensive isokinetics laboratory is neither optimal nor realistic in many team sports scenarios. IK training with the BioCircuit Leg Extension Machine is effective in improving lower body peak torque and power measures, as well as vertical jump and lower-body maximal strength performance in athletes. However, the significance of IK training on each fitness quality depends on repetition count and the velocity implemented, as maximal strength improves most significantly with low velocity (> 6 repetitions at 25°/s) training, and power measures benefit from higher velocity (> 6 repetitions at 80°/s) protocols.

BIA

Bioelectrical impedance analysis

BFP

body fat percentage

body mass

control group

CMJ

countermovement jump

effect size

EUR

eccentric utilization ratio

FFM

fat-free mass

fat mass

ICC

intraclass correlation coefficients

isokinetic training

IK25

isokinetic training at 25°/s

IK80

isokinetic training at 80°/s

isotonic training

P_peak

estimated peak power

peak torque

PT80

isokinetic peak torque at 80°/s

PT25

isokinetic peak torque at 25°/s

standard deviation

squat jump

thigh circumference

1-RM

one-repetition maximum

Ethics approval and consent to participate

Prior to the start of the study, ethical approval was obtained from the IST Hochschule ethics committee in accordance with the Declaration of Helsinki. All participants provided written informed consent before beginning and all data collection, protection, and analysis methods were performed in accordance with the ethical framework of the Declaration.

Consent for publication

Not applicable.

Availability of data and materials

The data generated during this study are partially included in this published article. The complete dataset is available from the corresponding author on request.

Competing interests

The authors declare that they have no competing interests.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Authors’ contributions

JW designed and performed the experiment under the supervision of SGeisler. SGavanda carried out the statistical analysis. JE composed the manuscript with input and editing from SGavanda.

Acknowledgements

We are deeply grateful for all athletes who participated in this study and for the hard work they put in every training session.

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No competing interests reported.

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Comparison of the effects of isokinetic and isotonic strength training in team sport athletes: A randomized controlled trial

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