Handball is an Olympic team sport that opposes 2 teams of 7 players on a court of 800 m2. It is characterized by playtime of 2 periods of 30 minutes including a wide range of defensive and offensive actions, such as duels, jumping, sprinting, shooting, and the ability of changing direction. These actions represent the majority of components in handball performance (24). They are invariably challenged during training and competition, where they regularly require high levels of strength and power for both quadriceps (Q) and hamstring (H) muscles (5,44). Several tests exist to assess the muscular characteristics of the lower limbs. The field tests, such as the 1-repetition maximum (1RM) test, allow to measure the maximum strength of a specific muscular movement. The squat jump test or countermovement jump test enables the measurement of vertical jump. However, those tests are not necessarily precise and reliable to follow-up the strength and power values. Recently, the mechanical capabilities of the neuromuscular system can be assessed by the linear “force-speed” relationship and the “power-speed” parabolic relation or ratio. The work of Jidovtseff (22) and Samozino et al. (34) focuses on determining the muscular profile of the athletes' lower limbs in an optimal strategy of developing maximum power. Nevertheless, all these field tests are primarily aimed at identifying the athletes' individual profiles and guiding the training contents. In addition to field tests, electromyography assessments and isokinetic testing can characterize muscle function. The most common evaluation is to assess both Q and H strength and power using a reliable and reproducible isokinetic device (23,25).
Some studies have centered its interests on the effects of an entire competition season on the isokinetic muscular characteristics in soccer (10,26) and basketball (19). Other studies have investigated on cardiorespiratory and muscular changes (strength and maximum power) during an entire competition season in handball (15,16,28), but no studies have been conducted in the longitudinal follow-up of muscular adaptations in world-class handball players over a full competitive season. The monitoring of isokinetic strength and muscle power throughout a full competitive season through measuring peak torque (PT) and mean power (MP) of Q and H will attempt to illustrate its effects in professional handball players belonging to the European elite and to reorient, if necessary, training methods during this time. At the very least, the analysis of available dominant-nondominant ratio (DNDR), agonist-antagonist ratio (AAR), and combined ratio (CR) would allow for the accurate and detailed assessment of muscular characteristics of each individual player, allowing for the prevention of injuries (39). The objective of this study was, therefore, to study the changes in the lower limbs, specifically the characteristics of the isokinetic muscles, during a full competitive season for world-class handball players. Our hypothesis was that a competitive season, including many games and training (15), maintains the values of isokinetic muscle strength and power.
Experimental Approach to the Problem
Throughout the season, the objective was to maintain peak performance level in all players. The training schedule required various actions, predominantly distributed between technical-tactical, game, and strength and endurance training sessions (Table 1). The 39-week competitive season, not including the precompetitive preparation period (Pc2P), was structured around several periods of strength and endurance development (Table 2).
The maximal strength training of lower limbs was performed at 90% intensity of 1RM. For hypertrophy development, exercise intensity was set as 70% of 1RM. The power development sessions, performed at intensities of 50–60% of 1RM and those of explosivity, executed at 30% of 1RM at maximum speed represented the largest number of sequences (Figure 1).
The endurance training emphasizing the development of aerobic capacity was tested at intensities ranging between 65 and 75% of maximum aerobic velocity. The maximum aerobic power intensity ranged at 110% of maximal aerobic velocity. Finally, the sessions of anaerobic power and repeated sprint ability were tested at maximal intensity (sprint). With the exception of bruises caused by body contacts between players, all injuries of the lower limbs have been listed throughout the competitive season (Figure 2).
An elite French handball team participated in this study. To address the objective of the study, the team was monitored during an entire competitive season. Measures of physical characteristics (such as stature, body mass, and fat) and isokinetic muscle strength (PT, MP, and different ratios) were analyzed at the start and the end of the competitive season.
On each day of the evaluation, after a standardized breakfast for all participants, subjects were tested in laboratory. These tests were always performed at the same time of day and in the same order for all the subjects. During this experimental phase, anthropometric measurements, including measurements of stature, body mass, and fat, were measured. Then, each subject performed an isokinetic test to establish a muscular profile. All subjects were familiar with the isokinetic evaluation. A complete 39-week competitive season heavily structured on physical, technical, and tactical work bridged the 2 testing days.
Nineteen, male, handball players, either French or foreign, and belonging to the professional League 1 (France) were recruited for the study. The players had a training experience (7.6 ± 1.3 years) of the highest level of expertise in France. Mean values (±SD) of age, stature, body mass, and fat were 26.6 ± 5.4 years, 189.5 ± 5.1 cm, 93.7 ± 11.9 kg, and 10.6 ± 2%, respectively. Inclusion criteria were the following: being a male and being under contract for a minimum of 3 years. The exclusion criteria were chronic or acute diseases and pain of the knees or lower limbs at testing and contraindicating maximal concentric and eccentric exercise. All subjects have written informed consent to participate in the experiment in accordance with the Declaration of Helsinki. The study protocols were approved by the Jules Verne University Ethics Committe (Amiens, Picardie, France) and were carried out in agreement with the head doctor and validated by the medical committee of the club.
Subjects were evaluated using a Biodex Isokinetic Dynamometer 3 System (Biodex, Corp., Shirley, NY, USA) with gravity correction. After Pc2P, 2 bilateral tests of knee joint flexors (H) and extensors (Q) were performed in concentric and eccentric modes at the beginning of season in September and at the end of season in June. The first test (Pre), which was performed after Pc2P, allowed for the individualization of muscle training sessions. The second test (Post) was performed at the end of the season and allowed for the study of the effects of a full competitive season on changes in PT, MP, DNDR, AAR, and CR values. The warm-up and set-up procedures were the same for both Pre and Post tests. Before the tests, the subjects warmed up on a cycle ergometer for 5 minutes by cycling against a load of 60 W at 90 rotations·min−1. This warm-up was followed by active dynamic stretching of the psoas, Q, H, and gastrocnemius muscles. The range of motion during the test was 70°, from −10° to 60° angle, between the femur and the tibia to limit hamstring resistance during the extension. The length of the lever arm was individually determined, depending of the height of each players, and the resistance pad was placed 2 fingers above the medial malleolus. The tests were performed bilaterally in a sitting position with a hip flexion angle of 110°, a trunk and waist strap, and the upper limbs crossed on the trunk. Each subject was placed in a comfortable position that did not limit knee movement. The height and depth of the seat relative to the dynamometer's rotational axis and the length of the lever arm relative to the rotational axis were stored in the computer program (Biodex Medical, Inc.) to standardize the test's conditions. During testing, subjects were verbally encouraged by the same experimenter and gripped the sides of the seat for support.
Each test was preceded by a standardized warm-up of 2 sets of 5 repetitions at 60°·s−1 in concentric mode separated by 1 minute of recovery, following the 3 minutes of the initial cycling warm-up. The protocol started with an evaluation in the concentric modes on the dominant leg, beginning with a series of 5 repetitions at 60°·s−1, followed by 1 minute of recovery, and then a final set of 5 repetitions at 240°·s−1. After 1 minute of recovery, evaluation of H at 30°·s−1 in eccentric mode concluded the first part of the test. During the following 5-minute recovery, the subjects were set up for the evaluation of the nondominant leg following the same procedure (32).
The values of PT and MP, expressed in absolute values and normalized by body mass, were used to calculate the DNDR and AAR, at 60 and 240°·s−1 in concentric mode. In addition, the evaluation in eccentric mode allowed us to calculate the CR (H values measured at 30°·s−1 in eccentric mode and the Q values measured at 240°·s−1 in concentric mode). The validity and the reproducibility of the used Biodex isokinetic dynamometer system have already been shown for all the parameters mentioned above by Drouin et al. (7).
Testing 1-Repetition Maximum
The 1RM test was measured on squat, deadlift, and step-up movement after a standardized warm-up, which began with cardiorespiratory activation (aerobic capacity training at 70–75% of HRmax) and then an articular mobilization of lower limbs (ankles, knees, and hips). Subsequently, subjects began with 2 sets of 8–10 repetitions at 50 and 60% of 1RM. After this, subjects then performed successive 1RM starting at approximately 75% of 1RM and increased by 5% until reaching 1RM. There was a rest interval of 2–3 minutes between the sets. Each subject had 2 attempts on the last performance to be executed (1).
Testing Maximal Aerobic Velocity
The 20-m shuttle run test was originally designed by Leger and Lambert (27). The test is based on the completion of repeated shuttle runs between 2 lines placed 20 m apart. The running speed is incremental and dictated by audio signals from a tape recorder. The aim of the test is to complete as many shuttle runs as possible.
Stature was measured using a Tanita HR-001 (Tanita, Corp., Tokyo, Japan). Body mass was measured with the players wearing light indoor clothing and no shoes, using a Tanita Body Composition Analysis (TBF-3000; Tanita, Corp.). Percentage of fat was estimated from 4 skinfold thicknesses (biceps, triceps, subscapular, and suprailiac), according to the method of Durnin and Rahaman (9). Fat-free mass was estimated as the difference between measured body mass and estimated fat.
All data are presented as mean ± SD. After conducting a test of normality, the nonparametric Wilcoxon's test for paired data was used to analyze the influence of entire competitive season on PT, MP, DNDR, AAR, and CR. The significance level was set at p ≤ 0.05. When significant differences were found, effect size (ES) was assessed from the Cohen's d. Effect size of 0.20–0.60, 0.61–1.19, and ≥1.20 was considered small, moderate, and large, respectively (21). Statistical analyses were performed with the SigmaStat 3.1 program (Jandel Scientific, San Rafael, CA, USA).
In concentric mode at 60°·s−1, PT showed a significant (p < 0.001) decrease in Q for dominant leg compared with nondominant leg throughout the competitive season (Figure 3). However, at 240°·s−1, no significant difference was observed in Q and H for both dominant and nondominant legs. In eccentric mode at 30°·s−1, the present results showed no significant difference for both dominant and nondominant legs. The Cohen's d ES was 0.19 (small) in Q and 0.38 (small) in H at 60°·s−1.
In concentric mode at 60°·s−1, the results of the present study showed no significant difference in Q and H for both sides throughout the season (Figure 4). At 240°·s−1, no significant difference was observed in Q for both dominant and nondominant legs and in H for only nondominant leg. In contrast, a significant decrease (p < 0.001) was observed in H for dominant leg. In eccentric mode at 30°·s−1, a significant increase (p < 0.001) was observed for both dominant and nondominant legs. The Cohen's d ES was 0.44 (small) in H at 240°·s−1 for dominant side, 0.10 (small) in H at 30°·s−1 for dominant side, and 0.15 (small) in H at 30°·s−1 for nondominant side.
Dominant-Nondominant, Agonist-Antagonist, and Combined Ratios
In concentric mode at 60°·s−1, a significant decrease was observed in Q (p < 0.03) for DNDR (Table 3). A significant decrease in AAR was observed at 240°·s−1 for dominant side (p < 0.01). No significant change was observed in CR.
This study aimed at evaluating the eventual change in muscular isokinetic parameters of the lower limbs in world-class handball players over a full competitive season. In concentric mode, except for PT values at 60°·s−1 on Q and MP values at 240°·s−1 on H for dominant side, which show a significant decrease, the general trend of the present results show that 39 weeks of high-intensity training and competition levels did not induce significant changes in strength and muscle power values of the knee joint, validating the experimental hypothesis.
The present results reflect those of Silva et al. (36) showing that professional soccer players participating in competitions maintain the isokinetic Q and H strength values at their initial values. The results are also in agreement with the study of Eniseler et al. (10), performed with Turkish professional footballers of the Super League level, that did not show significant effects of a 24-week training and competition period on PT values measured at 60°·s−1 or on maximum strength tested at high angular velocities (300 and 500°·s−1). The general trend of the present results could be explained by the variety of physical movements required by handball training, which involve the simultaneous development of several physical qualities. The high-level handball training requires strength and power, particularly of the lower limbs, and endurance via aerobic energy metabolism pathway solicitation (28). Because of this, endurance training sessions are regularly planned (Table 2) during a season, and they can significantly interfere with the development of strength (13) and muscular power. Some studies have shown that strength gains are inhibited by the addition of endurance training sequences (8,18,39), mainly because of a physiological interference between 2 signaling pathways. Strength training stimulates pathway of growth factors like insulin-like growth factor-1, thereby optimizing protein synthesis and thus the increase in strength and hypertrophy: mammalian-mechanistic target of rapamycin. However, endurance training stimulates the metabolism of carbohydrates and fatty acids: AMPK (metabolic activated protein kinase), which inhibits mammalian-mechanistic target of rapamycin and thus limits these training responses (6,31). Another explanation could be put forward to explain the general trend of the results of the present study. Indeed, the handball players studied were world-class athletes and according to the work of Häkkinen et al. (17), training-related adaptations are mainly dependent on the athlete's pretraining level. Because the studied physical qualities of handball players are already elevated, the amelioration of these qualities would be less important.
The end-of-season values observed in the present study therefore showed that the regular practice of handball (n = 180 technical-tactical sessions and n = 68 games sessions), associated with strength training sessions (n = 35) and endurance training sessions (n = 25), without Pc2P (Table 1) (a) allows to maintain isokinetic strength parameters (PT and MP at 60 and 240°·s−1) in Q and H for nondominant leg and (b) induced a significant decrease in PT values (p < 0.001) on dominant leg in concentric mode at 60°·s−1 in Q. At the high-competition level, many passes and throws (jump throw, standing throw, diving throw, and standing throw with run-up) are made during technical-tactical training sessions and games sessions (30,32). Like most broken-off throws (12), a throw or a pass in handball favors the exclusive use of a single arm (dominant side) and the use of the opposing leg (nondominant side). That is also true concerning one-on-one action (30), involving a dynamic lateral thrust during which the player most often uses the opposing lower limb (nondominant) to the hand carrying the ball (11). From a biomechanical point of view, this motor organization allows for better balance and thus a better force transference (42). The pelvis and the trunk can also pivot better and therefore induce a greater angular velocity in the acceleration phase of the hand carrying the ball (43). This motor organization allows a better automation of the coordination between the race, the jump, and the throw (11,43). However, this also induces a greater muscular exertion on the lower nondominant leg, explaining in part the maintenance of these strength indices at their initial levels.
Various explanations can be taken into consideration to justify the significant decrease in PT values at 60°·s−1 in Q for the dominant side. First, the dominant side was exerted less during throws, passes, and one-on-one action regularly practiced in handball. In handball, each action like a jump and explosive throw is performed with only 1 leg (14). This specific motor skill could partly explain the significant decrease observed on the dominant side at the end of the competitive season. This significant decrease could be offset by regular muscle strengthening sessions, but the quantity of these sessions was probably insufficient during the competitive season (Figure 1). Indeed, during a sports season, an elite-level handball team plays games at a consistent interval with an average of 2 matches per week for a total of approximately 60 official matches spanning through the national championship, the national cups, the European league, and the trophy of the champions. In addition to these matches, the players performed 180 training sessions focused on technical and tactical work. This framework specialized for high-level handball limits the time devoted to physical capacity development and, more particularly, the time devoted to the strength muscular quality development (20,35,37).
The MP values show a significant decrease (p < 0.001) on dominant side, in H during concentric mode at 240°·s−1 and a significant increase (p < 0.001) on dominant and nondominant sides in H at 30°·s−1. These results showed that the permanent H exertion under maximum tension during game actions, such as changes of direction, accelerations, and decelerations (38), did not maintain the value of 240°·s−1 on the dominant leg, which required less exertion by the specific motor organization. Second, to optimize the efficiency of these actions and to prevent injury in the athlete as much as possible, an appropriate program was offered throughout the competitive season. This program included targeted and individualized exercises that were performed in all contraction modes. Most often these exercises were performed in eccentric mode to reproduce the phase of lengthening found in numerous phases of fast accelerations with stops, short sprints with change in direction (2), which are regularly involved in the muscular injuries of the lower limbs. This would explain the significant increase (p < 0.001) observed in H at 30°·s−1.
During the actual investigation, we also studied AAR, DNDR, and CR. Authors such as Croisier et al. (4) showed that muscle strength of knee flexors and extensors should be well balanced to reduce the risk of injuries at the level of lower limbs. The results of the present study show a significant decrease in AAR (p < 0.01) on dominant side at 240°·s−1. This result supports the hypothesis according to which the handball player's motor skill of a cross-chain coordination between the carrying arm of the ball and the opposite foot requires far less exertion on the dominant side. However, the end-of-season ratio remained within normal. It was in range of the theoretical reference value (between 0.6 and 0.7) in concentric mode (3,23).
The DNDR showed a significant decrease at 60°·s−1 in Q (p < 0.03). However, the value of this ratio measured at the end of the competitive season remains close to 1.0. This value represents the reference standard from a functional and clinical point of view (3), although there is controversy over the notion of bilateral knee strength balance (41). Indeed, some authors (12,40) consider that a difference of more than 10% between values on one side compared with the other can be considered an imbalance. This is not the case in regard to the results of the present study, which indicated that regular practice of handball does not alter the muscle ratios.
Concerning CR, the present results did not show significant changes between the beginning and the end of the competitive season, with values located around 1.0 (1.02 vs. 0.99), considered as a reference value (40). The longitudinal follow-up of injuries, performed by the medical staff based on the quantification of the lower limbs injuries, showed 2 time frames during which injuries increased: from November to December and from March to April (Figure 2). This observation should serve as a basis for the analysis of preventive musculoskeletal disorders frequently encountered in high-level athletes and, as far as possible, should encourage all coaches to individually manage their athletes' preparation in relation to their muscular profile.
One limitation of this study is that muscle groups were tested using an isokinetic dynamometer with a monoarticular approach, although sports are played in a closed system, suggesting that several muscle groups contribute to athletic performance. Finally, it would have been interesting to carry out another midseason assessment to have intermediate control over the evolution of values. The inherent constraints for a team at this competition level (2 games per week) and the international calendar have failed to achieve this goal. Moreover, it was impossible to establish a control group with regard to the elite level of the team.
Given the general trend of the present results, which show that a full competitive season for world-class handball players did not induce significant changes in strength and muscle power values of the knee joint, it would be very interesting to increase these values at the beginning of the season to keep these high values as long as possible during the season. In team sports at highest level of practice, the most appropriate period to increase strength and muscle power is Pc2P (29), which lasts from 6 to 8 weeks depending on the sport discipline. As advised by the authors, intensive development of strength and power during Pc2P would maximize long-term effects, delaying a too fast and important decrease of strength and power values. In addition, despite the increase of matches on the calendar and to avoid falling values from decreasing and allowing an increase rather than a maintenance, a regular integration of strength training sessions during competition periods becomes a necessity. It could be done at the expense of some specific technical and tactical sessions not to add workload to the athletes. Finally, given (a) the importance of action, such as jumping, regularly found on the lower limbs in the specific actions of handball player at a higher level of competition and (b) the correlations observed between isokinetic strength values of knee extensors and vertical jump values (33), it could be also interesting to integrate, specific handball training and exercises that aim at maintaining the qualities of strength and muscle power. The vertical and horizontal jumping exercises, using the plyometric muscle contraction (which promotes intermuscular coordination) would make it possible to maximize the levels of strength and power of handball players.
The authors thank the professional handball players for their participation in this research. The authors have no financial or conflicts of interest to disclose. The results of the present study do not constitute endorsement by the National Strength and Conditioning Association.
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