Professional soccer players are often exposed to demanding training schedules, which may include repeated, high-intensity exercise sessions performed on consecutive days, multiple times per week (16). Each training session places high physical demands on players as they experience repeated moderate and rapid accelerations and decelerations, explosive jumps, and muscle damage from eccentric loading or contact trauma (25). Excessive volumes of intense training particularly with minimal recovery time, can place great physiological demands on the musculoskeletal, nervous, immune, and metabolic systems, potentially causing a negative effect on subsequent exercise performance (26) and predispose some players to overload injuries (3), especially during a congested fixture period in which players are required to compete and train repeatedly within a short time frame (10,28). Therefore, the capacity to recover from intense training and competition is considered an important determinant of subsequent performance (21).
To facilitate the recovery process, different postexercise recovery interventions have been suggested, broadly classified into 2 categories (4): (a) active recovery or (b) passive recovery. Active recovery may include jogging or submaximal running and stretching exercises. In practice, these popular and current active recovery strategies are used for the purposes of enhancing recovery during warm-down protocols both after training and after matches in professional soccer clubs (7). The theoretical overall advantage reported that submaximal running establishes a greater blood flow to muscles, prevents venous pooling in the muscles after exercise, facilitates restoration from metabolic perturbations, attenuates the induction of muscle soreness, and increases muscle-damage recovery (1,32). Static stretching after exercise is used as a preventative measure for delayed-onset muscle soreness and improved range of motion through dispersion of edema or tension reduction of the muscle-tendon unit (19), and to reduce musculotendinous stiffness (31).
Despite the popularity of the implementation of these aforementioned recovery strategies in team sports, there are doubts about how these recovery types influence the performance of the subsequent exercise probably because of methodological differences across studies, especially in relation with the variables used as performance or recovery criterion (11). Thus, further research is needed to explore more sensitive markers of recovery (33).
In this context, tensiomyography (TMG) is a very sensitive simple and noninvasive method for measuring skeletal muscle' contractile properties and their functional profile and response and adaptation (i.e., acute fatigue). This measurement is carried out under isometric conditions, in response to an electrical stimulus.
The inconclusive findings and the relatively few sensitive markers of preceding investigations suggest that further research is needed to solve the ambiguity of the relation between recovery interventions, athletic performance, and physiological parameters. Moreover, to our knowledge, there are no studies that have investigated contractile properties by using TMG in professional soccer players. Therefore, the aim of this study was to determine the effectiveness, if any, of active and passive recovery interventions performed immediately after a training session on muscle contractile properties using TMG and perceived muscle soreness 24 hours after the training. On the basis of the theory that light muscle activity may accelerate the return of homeostasis in exercised muscle, it was hypothesized that active recovery modality would be more effective than passive recovery in professional soccer players.
Experimental Approach to the Problem
A randomized fully controlled trial design, including 2 experimental sessions (Figure 1), was used to determine the effect of 2 posttraining recovery modalities on muscle contractile properties, using noninvasive TMG, and perceived muscle soreness 24 hours after a training session. It was considered that examining elite soccer players during their actual training period would increase the relevance and the applicability of the results. The 2 recovery modalities were as follows: (a) active recovery and (b) passive recovery. The participants were required to wear the same athletic equipment and measurements were conducted at the same time of the day to minimize the effect of diurnal variations on the selected parameters during the 2 experimental sessions.
Thirty-one professional soccer players (age: 23.5 ± 3.4 years; height: 179.9 ± 5.1 cm; body mass: 75.7 ± 4.2 kg) participated in this study. All the subjects were informed of the purpose of the study and gave their informed consent according to the Declaration of Helsinki. The study was approved by the Investigational Review Committee of the Department of Physical Education and Sport Sciences. The physical characteristics of the players are shown in Table 1.
The weekly training program during the competitive period included 6 training sessions in 5 days for a total training load of approximately 8–10 hours per week, an official match (usually on Sunday), and a free day after the match (on Monday). As far the intensity is concerned, the weekly pattern reaches a peak intensity by midweek and then tapers off to exhibit peak performance in the match.
Two consecutive experimental sessions were organized during the in-season soccer-training period (March). The testing sessions were conducted in a room at an ambient temperature 21–22° C. The participants were required to arrive in a rested state at the same time each morning during the 2 separate (24 hours) experimental sessions (9:30 hours). The first session was designed to collect the player's TMG measurements and perceived muscle soreness (pretest), followed by a 20-minute active warm-up adapted from Olsen et al. (22) to prevent lower limb injuries, during which the players carried out transit mobility, technique, balance, and power exercises. Immediately after, all the participants performed a standard soccer training consisting of a 45-minute program, including a 15-minute maximal intensity intermittent exercise (20 × 30 m, with a 30-second rest period between each sprint) (2) and a 30-minute group specific aerobic endurance drill (4 × 4 minutes of 5 a side game, including goalkeepers, in an area of 40 × 50 m, with a 3-minute active rest at 65% of maximal aerobic velocity between sets) (13). To ensure that the training load did not vary between experimental and control groups, the player's heart rate (HR) was recorded during the entire training unit (Polar Team System, Polar Electro, Kempele, Finland) and at the end of the session they were asked to provide a rating of perceived exertion (RPE) on a 15-point scale (6), ranging from “light” (6 points) to “maximal effort” (20 points). At the end of the training unit, all the players were randomly assigned to the active recovery group (N = 15) or the passive recovery group (N = 16). A second experimental session was organized to obtain the posttest values. The players performed the same test, administered in the same order than in the first trial. The participants received verbal encouragement by the coach to ensure they reached the correct level of effort.
Recovery Modalities. The recovery protocols to be performed at the end of the first experimental training session were as follows: active recovery consisted of 20 minutes of low-intensity exercises, including 12 minutes of submaximal running at 65% of maximal aerobic capacity (1) and 8 minutes of static stretching, involving 3 bilateral repeats of 30-second held stretches to the hamstring, quadriceps, gastrocnemius, and adductor muscles (31); passive recovery during which the players sat on a bench, lasted 20 minutes, according to the duration of the active recovery protocol. The players were instructed to not do any other form of recovery procedure (i.e., massage, cold water immersion, etc.) during the 2 experimental sessions.
Tensiomyography Measuring Protocol. Tensiomyography is used to evaluate fatigued muscle responses and the effects of different recovery methods on muscle contractile properties (5). This technique is a noninvasive means of muscular assessment in which no physical effort is required of the player being evaluated. A displacement-measuring sensor recorded the geometric changes (radial displacement) that occurred in the muscle belly when a contraction was produced in response to an external electrical stimulus (18). The TMG displacement-time curve recordings allow muscle contractile properties to be assessed, obtain different parameters, which can inform about muscle tone. The main muscle contraction parameters are: maximal radial displacement (D m), contraction time (T c), delay time (T d). These parameters seem to show largest influence to muscle fatigue rate (18). The D m was given by the radial movement of muscle belly expressed in millimeters and depends on the muscle tone or stiffness, the decrease in D m being an indicator of increased muscular stiffness. High scores, by contrast, indicate a lack of muscle tone. The T d, also known as reaction time or activation time, represented the time it took to reach 10% of total movement after stimulation. The T c was obtained by recording the time from the end of the reaction time (10% deformation of the muscle belly) up to 90% of maximum deformation. Therefore, associating the decrease in D m with the increase in T c and T d supports the hypothesis that muscular fatigue is present in the muscle (18).
The evaluation was made on 2 muscle groups: rectus femoris (RF) and biceps femoris (BF) at dominant leg. Measurements were performed under static and relaxed conditions, with the subject in the supine and prone positions, for the measure of RF (Figure 2) and BF (Figure 3) muscles, respectively. In the supine position, the knee joint was fixed at a 120° angle (180° corresponding to full extension of the knee). The measured limb was positioned on a triangular wedge foam cushion to keep a fixed knee angle. A digital displacement transducer Dc-Dc Trans-Tek (GK 40, Panoptik d.o.o., Ljubljana, Slovenia), which incorporates a spring of 0.17 N·mm−1, was set perpendicular to the muscle belly to acquire RF and BF radial displacement. Sensor location was determined anatomically according to Delagi et al. (9) and marked with a dermatological pen. Both electrodes (5 × 5 cm) are placed symmetric to sensor; positive electrode (anode) is placed proximal and negative electrode (cathode) distal, 50–60 mm from measuring point. Electrodes are self-adhesive (Compex Medical SA, Ecublens, Switzerland). Constant electrical stimulation (75 mAp) was made with a TMG-S1 electrostimulator (Furlan Co. & Ltd., Ljubljana, Slovenia).
All measurements were made by the same physical therapist, which was experienced with taking these measurements. In any case, none of the participants reported discomfort during electrical stimulation.
The extent to which this method may be reproduced and is considered valid was assessed by Krizaj et al. (18) and Carrasco et al. (6) following the measurement protocol proposed by the manufacturers. The intraclass correlation coefficient (ICC) scores (95%) for TMG variables using in this study ranged from 0.89 to 0.92 as previously described (6).
Muscle Soreness. The players also completed a 7-point Likert psychophysical category scale designed to measure muscle soreness (20). The scale consisted of the following verbal anchors: 1 = very, very good; 2 = very good; 3 = good; 4 = tender but not sore; 5 = sore; 6 = very sore; and 7 = very, very sore.
Diet Control and Fluid Intake. In the early of 2 experimental sessions, the subjects were provided with individual 250-ml water bottles and were encouraged to drink ad libitum before, during, and after the training. The players were instructed to drink only from their own bottles. The food intake was standardized for all the players during the whole study period. To diet control, each participant was given a meal plan composed by a nutritionist (29).
Data are presented as means ± SD. A 0.05 level of confidence was selected throughout the study. Statistical analyses were conducted using the statistical package SPSS for Macintosh (version 18.0, Chicago, IL, USA). To evaluate the stability of the training load between groups (active vs. passive) according to the HR and RPE values, independent-samples t-test and Mann-Whitney U test were used, respectively.
To study the effectiveness of different postgame recovery interventions, the independent variable was the type of recovery (active and passive) and dependent variables were the TMG parameters (D m, T c, and T d) and muscle soreness. A multivariate analysis of variance with testing time (pre-post) as within-factor and recovery modes (active, passive) as between-factor, using absolute values, was applied to TMG performance and perceived muscle soreness. Furthermore, to provide meaningful analysis for comparisons from small groups, the Cohen's effect sizes (ESs) were also calculated. An ES ≤ 0.2 was considered trivial, from 0.3 to 0.6 small, <1.2 moderate and >1.2 large (14).
Stability of Training Load
There were no significant differences in the RPE (Figure 4) and HR between groups during training session. The average of HR for passive and active recovery was similar (166 ± 6 and 164 ± 6 b·min−1, respectively, p > 0.05). Altogether, the levels of RPE and HR values indicate the relative high intensity of the training and the homogeneity of training load between active and passive group.
Effects of Recovery Interventions
Means and SDs for the TMG measurements are presented in Table 2. There were no significant differences in absolute values for T d, T c, and D m of BF and RF muscles between baseline and posttest in active and passive recovery groups. Moreover, no significant effect because of recovery interventions was found on TMG measurements. However, mean recovery approached 100% for each recovery intervention (Figure 5). Generally, trivial to small ESs were found (range, 0–0.52).
At baseline, ratings of muscle soreness ranged from 4.1 to 4.5 (“tender but not sore”) (Table 3). Mean values were highest 24 hours after the training (“sore” to “very sore”), but only a significant change was observed in passive recovery group (p < 0.05). No significant differences were recorded between recovery interventions on perceived muscle soreness. Trivial to small ESs were found (0.25–0.51).
The ability to recover after intense training or competitive bouts is important to maintain or even increase performance in subsequent efforts. However, to our knowledge, there are only 3 scientific reports evaluating the effects of active recovery in male soccer players, which reported inconclusive findings (17,27,32), probably because of the relatively small sample size, the few sensitive markers employed, and participants' characteristics. Thus, this study was mainly designed to investigate the effects of immediate posttraining active and passive recovery interventions on muscle contractile properties, using a sensible and noninvasive method (TMG), and perceived muscle soreness in professional soccer players.
The main findings of this study were (a) active recovery, after specific soccer training, did not have a positive effect on TMG measurements and muscle soreness compared with passive recovery modality (Table 2); (b) a significant increase on perceived muscle soreness 24 hours after specific soccer training in passive recovery group (Table 3). However, this study has 3 potential limitations. The first is that the observation period (2 experimental sessions) might be too short to evaluate the effect of recovery interventions over the time. A longer period is needed (e.g., 1 week) to analyze the effectiveness of the 2 types of rest in detail. However, it is unfeasible to hypothesize that coaches and professional players will be available for a longer experimental study, which could interfere with their training program. The second limitation is that other recovery indicators such as metabolites removal and the rate of postexercise glycogen synthesis were not included in the study in an attempt to keep it simple, noninvasive, and practical. Third is the use of a single, practical, short-term physiological measure to assess performance change. Consequently, it is not known how the different recovery methods impact on longer duration physical or physiological performance such as intermittent running (17).
In this study, a standard training session was administrated and the player's HR and RPE were used to monitor their training intensity. The lack of significant differences between experimental and control group for both HR and RPE confirms that the same training load was administrated. The HR was in agreement with that reported previously for an intense training workload in professional soccer players (13). The participants perceived the intensity of the training as hard, similar to that observed by Impellizzeri et al. (15).
Although there are several differences related to experimental protocol (i.e., fatiguing exercises, sample size, duration, and characteristics of active recovery protocol), the results of this investigation are consistent with those of previous studies in which active and passive recovery were tested as recovery methods (17,27,32).
An innovation of this study was the use of TMG to evaluate the effects of different recovery interventions on contractile properties of fatiguing muscles in soccer players. The D m is being considered as a measure of muscle belly stiffness (33). Contraction time parameters such as T c and T d show largest influence to muscle fatigue rate (18). There were no statistical differences in TMG data when time × recovery methods intersection analysis was performed. These results indicate that there was no recovery effect of active recovery on the fatigued RF and BF because its contractile properties after passive recovery were similar. However, the outcome data showed a nonsignificant better recovery in 2 TMG parameters, BF D m and RF T d, in active recovery group indicating an enhanced contractile capacity with respect to passive recovery group (Figure 5). One possible explanation of this trend may be the theoretical overall advantages of static stretching that possibly will cause a decrease in musculotendinous stiffness and tension reduction of muscle-tendon unit (19,31). To our knowledge, there is only one scientific report evaluating the effects of different recovery interventions on muscle contractile properties using TMG (5). The study was on recreationally active male volunteers who performed a 15 minutes of low-frequency vibration recovery method after a fatiguing exercise (2 minutes of cycling protocol). Their results showed no effect of recovery strategy on the assessed variables. However, the short duration of fatigued protocol may not lead to exhaustion; therefore, the resulting recovery was probably too rapid to be improved by the recovery intervention. Despite the lack of TMG research in soccer, various studies have analyzed the electromyography activity of major muscles of the lower extremity during and after soccer-specific intermittent treadmill protocol (12,23). The overall results of these studies show that the activity profile of soccer induces cumulative mechanical load on the musculoskeletal system. Assuming that the muscular fatigue, typical of soccer trainings and games, leads to a reduction in muscle contractile properties because of the duration, magnitude and type of contraction, it is likely that this decrease is the cause of the reduced muscle torque reported during repeated isokinetic efforts (24). Therefore, further investigations are recommended to understand the beneficial effect of these recovery interventions on other sensible variables in professional soccer players.
The potential for psychological factors influencing the individual's performance is crucial for coaches (32). The muscle soreness ratings reported in this investigation are in agreement with those of previous studies in team sports (8,17). Despite the nonsignificant effect of the recovery mode in perceived muscle pain observed, significantly higher mean subjective ratings were found in passive recovery group 24 hours after training, indicating that active recovery could represent a valuable aid for muscle recovery to improve the player's attitude toward training (32).
In summary, this study showed no significant differences between the effects of active and passive recovery strategies on muscle contractile properties and perceived muscle soreness after soccer training in soccer.
The primary finding of this study is that the use of active recovery improves specific perception of muscle soreness. Thus, the use of active recovery strategies can improve the readiness of elite soccer players for matches or training sessions. A lower perception of muscle soreness could have a positive effect on the player's work attitude during subsequent training sessions. Furthermore, coaches could be advised to use subjective questionnaires to monitor the recovery stress of the athlete, especially when the competitive season requires frequent games.
In addition, this study provides normative data for professional soccer players of muscle contractile properties using TMG, so that the conditioning coach can use this information to determine standards of recovery in preseason and competition period. Performance standards for muscle contractile properties can be used to predict and guide the prescription of future training load in elite soccer and to prevent the risk of muscle injuries.
The lack of significant effects of active modalities on muscular recovery suggest further studies are necessary to address and determine the optimum quantity and quality of exercise during active recovery period depending of the training and players characteristics. Coaches also should give consideration to appropriate diet, rehydration, and an adequate passive rest and sufficient sleep (30). The underlying mechanisms of recovery after soccer training in professional players remain debatable. It is possible to hypothesize that longitudinal research protocols could be more successful in providing valuable information for the coach on the effectiveness of recovery interventions.
This study was supported by grants from Catedra Real Madrid. The authors would like to thank the players participating in this study.
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Keywords:Copyright © 2012 by the National Strength & Conditioning Association.
association football; regeneration; warm-down; fatigue