Effects of active recovery under a decreasing work load following intense muscular exercise on intramuscular energy metabolism

Muscle fatigue tracking during dynamic elbow flexion-extension movements with a varying hand load

Muscle fatigue monitoring, an important element in a fatigue risk management process, can help optimize work intensity and reduce risks for musculoskeletal injuries. An experiment was conducted to determine whether myoelectric manifestations of muscle fatigue can reflect the pace of fatigue development associated with varying load intensity. Twenty male participants performed elbow flexion-extension movements with alternating hand loads (2 kg vs. 1 kg) for 16 min. The pace of fatigue in the biceps brachii in response to load variation was quantified by electromyographic (EMG) fatigue measures collected during the dynamic elbow flexion-extension movements and periodic submaximal isometric elbow flexion trials. The isometric and dynamic EMG measures, except for the amplitude of dynamic EMG, indicated fatigue development during the 2-kg isotonic movements and partial recovery with the 1 kg load. Study results suggest the potential of EMG measures for fatigue monitoring during dynamic work tasks with varying load intensity.

The effect of task rotation on activation and fatigue response of rotator cuff muscles during overhead work

Overhead work is known as one of the ergonomic risk factors that can lead to shoulder overload and injury. Anatomical alignment of rotator cuff muscles makes them the most vulnerable to injuries during overhead work. In this study, the effect of task rotation, as one of the administrative controls to reduce the risk of injury during overhead work, on the fatigue response of rotator cuff muscles was investigated. Twelve participants performed three submaximal exertions (5, 20, and 35% of maximum voluntary contraction (MVC)) using four task rotation sequences (increasing, decreasing, upward parabolic, and downward parabolic). Median frequency of surface electromyography (EMG), shoulder strength, and ratings of perceived exertion (RPE) were used to study the fatigue response of rotator cuff muscles. Although the average normalized muscle activity was similar in all sequences, the task rotation sequence had a significant effect on the median frequency. The effect of task rotation sequence on the strength and RPE was similar to that of the median frequency but was statistically not significant. The upward parabolic task rotation sequence resulted in the lowest fatigue among all the task sequences. Performing intense exertions apart from each other, warm-up exertions, and the presence of active recovery after the intense exertions could be the factors that produced the lowest fatigue during this sequence.

Acute effect of inspiratory resistive loading on sprint interval exercise performance in team-sport athletes

This study examined acute effects of inspiratory resistive loading (IRL) during rest intervals on sprint interval exercise (SIE) performance. In a randomized crossover design, nine collegiate basketball players performed IRL (15 cmH₂O) or passive recovery (CON) at 5-min rest intervals during and immediately after 6 sets of a 30-s SIE test. Performance, muscular oxygenation of vastus lateralis, blood lactate and pH were measured at each condition. Blood lactate at 5-min (-20.5 %) and 20-min (-21.3 %) after SIE were significantly lower in IRL than in CON. The pH at 5-min after SIE was significantly higher in IRL than in CON (+0.8 %, p <  0.05). However, the total work in IRL was significantly lower than in CON (-2.7 %, p <  0.05). Average changes in total hemoglobin at rest intervals in IRL were significantly lower than in CON (-34.5 %, p <  0.05). The IRL could attenuate exercise-induced metabolic acidosis; however, the decreased blood flow at rest intervals might increase the physical challenge in SIE.

Infrared Low-Level Laser Therapy (Photobiomodulation Therapy) before Intense Progressive Running Test of High-Level Soccer Players: Effects on Functional, Muscle Damage, Inflammatory, and Oxidative Stress Markers-A Randomized Controlled Trial

The effects of preexercise photobiomodulation therapy (PBMT) to enhance performance, accelerate recovery, and attenuate exercise-induced oxidative stress were still not fully investigated, especially in high-level athletes. The aim of this study was to evaluate the effects of PBMT (using infrared low-level laser therapy) applied before a progressive running test on functional aspects, muscle damage, and inflammatory and oxidative stress markers in high-level soccer players. A randomized, triple-blind, placebo-controlled crossover trial was performed. Twenty-two high-level male soccer players from the same team were recruited and treated with active PBMT and placebo. The order of interventions was randomized. Immediately after the application of active PBMT or placebo, the volunteers performed a standardized high-intensity progressive running test (ergospirometry test) until exhaustion. We analyzed rates of oxygen uptake (VO_{2 max}), time until exhaustion, and aerobic and anaerobic threshold during the intense progressive running test. Creatine kinase (CK) and lactate dehydrogenase (LDH) activities, levels of interleukin-1β (IL-1-β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNF-α), levels of thiobarbituric acid (TBARS) and carbonylated proteins, and catalase (CAT) and superoxide dismutase (SOD) activities were measured before and five minutes after the end of the test. PBMT increased the VO_{2 max} (both relative and absolute values—p < 0.0467 and p < 0.0013, respectively), time until exhaustion (p < 0.0043), time (p < 0.0007) and volume (p < 0.0355) in which anaerobic threshold happened, and volume in which aerobic threshold happened (p < 0.0068). Moreover, PBMT decreased CK (p < 0.0001) and LDH (p < 0.0001) activities. Regarding the cytokines, PBMT decreased only IL-6 (p < 0.0001). Finally, PBMT decreased TBARS (p < 0.0001) and carbonylated protein levels (p < 0.01) and increased SOD (p < 0.0001)and CAT (p < 0.0001) activities. The findings of this study demonstrate that preexercise PBMT acts on different functional aspects and biochemical markers. Moreover, preexercise PBMT seems to play an important antioxidant effect, decreasing exercise-induced oxidative stress and consequently enhancing athletic performance and improving postexercise recovery. This trial is registered with Clinicaltrials.gov NCT03803956.

MR compatible ergometers for dynamic 31P MRS

Magnetic Resonance (MR) compatible ergometers are specialized ergometers used inside the MR scanners for the characterization of tissue metabolism changes during physical stress. They are most commonly used for dynamic phosphorous magnetic resonance spectroscopy (31P MRS), but can also be used for lactate production measurements, perfusion studies using arterial spin labelling or muscle oxygenation measurements by blood oxygen dependent contrast sequences. We will primarily discuss the importance of ergometers in the context of dynamic 31P MRS. Dynamic 31P MRS can monitor muscle fatigue and energy reserve during muscle contractions as well as the dynamics of recuperation of skeletal muscle tissue during the following recovery through signal changes of phosphocreatine (PCr), inorganic phosphate and adenosine triphosphate (ATP). Based on the measured data it is possible to calculate intracellular pH, metabolic flux of ATP through creatine-kinase reaction, anaerobic glycolysis and oxidative phosphorylation and other metabolic parameters as mitochondrial capacity. This review primarily focuses on describing various technical designs of MR compatible ergometers for dynamic 31P MRS that must be constructed with respect to the presence of magnetic field. It is also expected that the construction of ergometers will be easy for the handling and well accepted by examined subjects.

Active recovery intervals restore initial performance after repeated sprints in swimming

The purpose of this study was to examine the effects of active recovery (AR) and passive recovery (PR) using short (2-min) and long (4-min) intervals on swimming performance. Twelve male competitive swimmers completed a progressively increasing speed test of 7 × 200-m swimming repetitions to locate the speed before the onset of curvilinear increase in blood lactate concentration (LT₁). Subsequently, performance time of 6 × 50-m sprints was recorded during four different conditions: (i) 2-min PR (PR-2), (ii) 4-min PR (PR-4), (iii) 2-min AR (AR-2) and (iv) 4-min AR (AR-4) intervals. Blood lactate concentration was measured before the first and after the last 50-m repetition. AR was applied at an intensity corresponding to LT₁. Performance as indicated by the time needed to complete 6 × 50-m sprints was impaired after AR-4 compared to PR-4 (AR-4: 28.65 ± 1.04, PR-4: 28.17 ± 0.72 s; mean% difference: MD% ±s; ±90% confidence limits: 90%CL, 1.71 ± 3.01%; ±1.43%, p = .01) but was not different between AR-2 compared to PR-2 conditions (AR-2: 28.68 ± 0.85, PR-2: 28.69 ± 0.82 s; MD%: 0.03 ± 1.61%; 90%CL ± 0.77%, p = .99). Performance in sprint-6 was improved after AR compared to PR independent of interval duration (AR: 28.55 ± 0.81, PR: 29.01 ± 1.03 s; MD%: 1.52 ± 2.61%; 90%CL ± 1.2%; p = .03). Blood lactate concentration was lower after AR-4 compared to PR-4 but did not differ between AR-2 and PR-2 conditions. In conclusion, AR impaired performance after a 4-min but not after a 2-min interval. A better performance during sprint-6 after AR could be attributed to a faster metabolic recovery or anticipatory regulatory mechanisms towards the end of the series especially when adequate 4-min active recovery interval is applied.

Effect of self-paced active recovery and passive recovery on blood lactate removal following a 200 m freestyle swimming trial

Purpose

The aim of this study was to investigate the effect of self-paced active recovery (AR) and passive recovery (PR) on blood lactate removal following a 200 m freestyle swimming trial.

Patients and methods

Fourteen young swimmers (with a training frequency of 6–8 sessions per week) performed two maximal 200 m freestyle trials followed by 15 minutes of different recovery methods, on separate days. Recovery was performed with 15 minutes of passive rest or 5 minutes of passive rest and 10 minutes of self-paced AR. Performance variables (trial velocity and time), recovery variables (distance covered and AR velocity), and physiological variables (blood lactate production, blood lactate removal, and removal velocity) were assessed and compared.

Results

There was no difference between trial times in both conditions (PR: 125.86±7.92 s; AR: 125.71±8.21 s; p=0.752). AR velocity was 69.10±3.02% of 200 m freestyle trial velocity in AR. Blood lactate production was not different between conditions (PR: 8.82±2.47 mmol L⁻¹; AR: 7.85±2.05 mmol L⁻¹; p=0.069). However, blood lactate removal was higher in AR (PR: 1.76±1.70 mmol L⁻¹; AR: 4.30±1.74 mmol L⁻¹; p<0.001). The velocity of blood lactate removal was significantly higher in AR (PR: 0.18±0.17 mmol L⁻¹ min⁻¹; AR: 0.43±0.17 mmol L⁻¹ min⁻¹; p<0.001).

Conclusion

Self-paced AR shows a higher velocity of blood lactate removal than PR. These data suggest that athletes may be able to choose the best recovery intensity themselves.

Active Recovery between Interval Bouts Reduces Blood Lactate While Improving Subsequent Exercise Performance in Trained Men

This study aimed to examine the blood lactate and blood pH kinetics during high-intensity interval training. Seventeen well-trained athletes exercised on two different occasions. Exercises consisted of three 30 s bouts at a constant intensity (90% of peak power) with 4 min recovery between bouts followed by a Wingate test (WT). The recoveries were either active recovery (at 60% of the lactate threshold intensity) or passive recovery (resting at sitting position). During the exercise, blood samples were taken to determine blood gasses, blood lactate, and blood pH, and peak and average power were calculated for the WT. When performing the active recovery trials, blood pH was significantly higher (p < 0.01) and blood lactate was significantly lower (p < 0.01) compared with the passive recovery trials. WT performance was significantly higher in the active recovery trials: peak power was 671 ± 88 and 715 ± 108 watts, and average power was 510 ± 70 and 548 ± 73 watts (passive and active respectively; p < 0.01). However, no statistically significant correlations were found between the increased pH and the increased performance in the active recovery trials. These results suggest that active recovery performed during high-intensity interval exercise favors the performance in a following WT. Moreover, the blood pH variations associated with active recovery did not explain the enhanced performance.

Rotation during lifting tasks: effects of rotation frequency and task order on localized muscle fatigue and performance

Though widely considered to reduce the risk of work-related musculoskeletal disorders, there is limited evidence suggesting that rotating between tasks is effective in doing so. The purpose of the current study was to quantify the effects of rotation and parameters of rotation (frequency and task order) on muscle fatigue and performance. This was done using a simulated lifting task, with rotation between two levels of loading of the same muscle groups. Twelve participants completed six experimental sessions during which repetitive box lifting was performed for one hour either with or without rotation. When rotation was present, it occurred every 15 minutes or every 30 minutes and was between two load levels (box weights). Rotation reduced fatigue and cardiovascular demand compared to the heavier load without rotation, with a mean reduction of ∼33% in perceived discomfort and a ∼17% reduction in percentage of heart rate reserve. Further, rotation increased fatigue and cardiovascular demand compared to the lighter load without rotation, with a mean increase of ∼34% perceived discomfort and a ∼19% increase in percentage of heart rate reserve. Neither rotation frequency nor task order had definitive effects, though maximum discomfort ratings were nearly 20% higher when starting with the lighter load task. These parameters of rotation should be further evaluated under more realistic task conditions.

Recovery in soccer : part ii-recovery strategies

In the formerly published part I of this two-part review, we examined fatigue after soccer matchplay and recovery kinetics of physical performance, and cognitive, subjective and biological markers. To reduce the magnitude of fatigue and to accelerate the time to fully recover after completion, several recovery strategies are now used in professional soccer teams. During congested fixture schedules, recovery strategies are highly required to alleviate post-match fatigue, and then to regain performance faster and reduce the risk of injury. Fatigue following competition is multifactorial and mainly related to dehydration, glycogen depletion, muscle damage and mental fatigue. Recovery strategies should consequently be targeted against the major causes of fatigue. Strategies reviewed in part II of this article were nutritional intake, cold water immersion, sleeping, active recovery, stretching, compression garments, massage and electrical stimulation. Some strategies such as hydration, diet and sleep are effective in their ability to counteract the fatigue mechanisms. Providing milk drinks to players at the end of competition and a meal containing high-glycaemic index carbohydrate and protein within the hour following the match are effective in replenishing substrate stores and optimizing muscle-damage repair. Sleep is an essential part of recovery management. Sleep disturbance after a match is common and can negatively impact on the recovery process. Cold water immersion is effective during acute periods of match congestion in order to regain performance levels faster and repress the acute inflammatory process. Scientific evidence for other strategies reviewed in their ability to accelerate the return to the initial level of performance is still lacking. These include active recovery, stretching, compression garments, massage and electrical stimulation. While this does not mean that these strategies do not aid the recovery process, the protocols implemented up until now do not significantly accelerate the return to initial levels of performance in comparison with a control condition. In conclusion, scientific evidence to support the use of strategies commonly used during recovery is lacking. Additional research is required in this area in order to help practitioners establish an efficient recovery protocol immediately after matchplay, but also for the following days. Future studies could focus on the chronic effects of recovery strategies, on combinations of recovery protocols and on the effects of recovery strategies inducing an anti-inflammatory or a pro-inflammatory response.

Effects of rotation frequency and task order on localised muscle fatigue and performance during repetitive static shoulder exertions

Though widely considered to reduce physical exposures and increase exposure variation, there is limited evidence that rotating between tasks is effective in reducing the risk of work-related musculoskeletal disorders (WMSDs). The purpose of this study was to assess the effects of rotation, specifically focusing on rotation frequency and task order, on muscle fatigue and performance when rotating between tasks that load the same muscle group. Twelve participants completed six experimental sessions during which repetitive static shoulder abduction tasks were performed at two exertion levels for one hour either with or without rotation. Compared to only performing a higher or lower exertion task, rotating between the two tasks decreased and increased fatigue, respectively. Increasing rotation frequency adversely affected task performance, and task order had a minor effect on muscle fatigue. These rotation parameters may be important considerations when implementing rotation in the workplace.

PRACTITIONER SUMMARY

Rotation is widely used and assumed to reduce the risk of WMSDs, yet little research supports that it is effective in doing so. Results here show that specific aspects of a rotation scheme may influence muscle fatigue and task performance, though further research is needed under more realistic task conditions.

Effects of recovery method after exercise on performance, immune changes, and psychological outcomes

STUDY DESIGN

Randomized controlled trial using a repeated-measures design.

OBJECTIVES

To examine the effects of commonly used recovery interventions on time trial performance, immune changes, and psychological outcomes.

BACKGROUND

The use of cryotherapy is popular among athletes, but few studies have simultaneously examined physiological and psychological responses to different recovery strategies.

METHODS

Nine active men performed 3 trials, consisting of three 50-kJ "all out" cycling bouts, with 20 minutes of recovery after each bout. In a randomized order, different recovery interventions were applied after each ride for a given visit: rest, active recovery (cycling at 50 W), or cryotherapy (cold tub with water at 10°C). Blood samples obtained during each session were analyzed for lactate, IL-6, total leukocyte, neutrophil, and lymphocyte cell counts. Self-assessments of pain, perceived exertion, and lower extremity sensations were also completed.

RESULTS

Time trial performance averaged 118 ± 10 seconds (mean ± SEM) for bout 1 and was 8% and 14% slower during bouts 2 (128 ± 11 seconds) and 3 (134 ± 11 seconds), respectively, with no difference between interventions (time effect, P≤.05). Recovery intervention did not influence lactate or IL-6, although greater mobilization of total leukocytes and neutrophils was observed with cryotherapy. Lymphopenia during recovery was greater with cryotherapy. Participants reported that their lower extremities felt better after cryotherapy (mean ± SEM, 6.0 ± 0.7 out of 10) versus active recovery (4.8 ± 0.9) or rest (2.8 ± 0.6) (trial effect, P≤.05).

CONCLUSION

Common recovery interventions did not influence performance, although cryotherapy created greater immune cell perturbation and the perception that the participants' lower extremities felt better.

Effects of active and passive recovery on performance during repeated-sprint swimming

The effect of active and passive recovery on repeated-sprint swimming bouts was studied in eight elite swimmers. Participants performed three trials of two sets of front crawl swims with 5 min rest between sets. Set A consisted of four 30-s bouts of high-intensity tethered swimming separated by 30 s passive rest, whereas Set B consisted of four 50-yard maximal-sprint swimming repetitions at intervals of 2 min. Recovery was active only between sets (AP trial), between sets and repetitions of Set B (AA trial) or passive throughout (PP trial). Performance during and metabolic responses after Set A were similar between trials. Blood lactate concentration after Set B was higher and blood pH was lower in the PP (18.29 +/- 1.31 mmol x l(-1) and 7.12 +/- 0.11 respectively) and AP (17.56 +/- 1.22 mmol x l(-1) and 7.14 +/- 0.11 respectively) trials compared with the AA (14.13 +/- 1.56 mmol x l(-1) and 7.23 +/- 0.10 respectively) trial (P < 0.01). Performance time during Set B was not different between trials (P > 0.05), but the decline in performance during Set B of the AP trial was less marked than in the AA or PP trials (main effect of sprints, P < 0.05). Results suggest that active recovery (60% of the 100-m pace) could be beneficial between training sets, and may compromise swimming performance between repetitions when recovery durations are short (< 2 min).

Métodos de recuperação pós-exercício: uma revisão sistemática

A recuperação pós-exercício consiste em restaurar os sistemas do corpo a sua condição basal, proporcionando equilíbrio e prevenindo a instalação de lesões e, nesse sentido, torna-se aspecto importante de todo programa de condicionamento físico, em quaisquer níveis de desempenho, mas, sobretudo nos mais elevados. O objetivo desta revisão foi reunir informações e descrever as respostas proporcionadas por métodos recuperativos pós-exercício, como crioterapia, contraste, massagem e recuperação ativa, constituindo uma fonte de atualização do referido tema. Utilizaram-se os bancos de dados MedLine, Scielo e Lilacs, como lista de periódicos, o SportsDiscus. Foram incluídos no estudo somente ensaios clínicos randomizados controlados e não-controlados, além de artigos de revisão referentes ao tema proposto. Optou-se por procurar os termos: cryotherapy, massage, active recovery, thermotherapy, immersion e exercise, individualmente e em cruzamentos. Como achado, observou-se que alguns estudos relatam que a crioterapia é prejudicial em se tratando de recuperação pós-exercício, pois reduz o desempenho imediatamente após a aplicação da técnica. Por outro lado, estudos apontam como sendo benéfica, pois reduzem o nível de creatinaquinase após alta intensidade de esforço, evitando danos musculares. Para o contraste, embora apresente significância em se tratando de remoção de lactato sanguíneo, sua efetividade necessita ser mais bem discutida. Na massagem e na recuperação ativa, os principais vieses descritos dizem respeito à pressão exercida e à intensidade do exercício, respectivamente. Entre as técnicas, as que parecem ter efeitos semelhantes são o contraste e a recuperação ativa, no que tange à remoção de lactato e diminuição da creatinaquinase. Ressalta-se que o tempo de exposição é de fundamental importância para todos os métodos. Entretanto, diversos estudos não se propõem a identificar os reais efeitos fisiológicos promovidos pelas técnicas, utilizando-as de modo inipiente. Portanto, a inconsistência dos resultados encontrados sugere que a análise das variáveis utilizadas como método de recuperação deve ser mais bem controlada.

Swimming performance after passive and active recovery of various durations

PURPOSE

To examine the effects of active and passive recovery of various durations after a 100-m swimming test performed at maximal effort.

METHODS

Eleven competitive swimmers (5 males, 6 females, age: 17.3 +/- 0.6 y) completed two 100-m tests with a 15-min interval at a maximum swimming effort under three experimental conditions. The recovery between tests was 15 min passive (PAS), 5 min active, and 10 min passive (5ACT) or 10 min active and 5 min passive (10ACT). Self-selected active recovery started immediately after the first test, corresponding to 60 +/- 5% of the 100-m time. Blood samples were taken at rest, 5, 10, and 15 min after the first as well as 5 min after the second 100-m test for blood lactate determination. Heart rate was also recorded during the corresponding periods.

RESULTS

Performance time of the first 100 m was not different between conditions (P > .05). The second 100-m test after the 5ACT (64.49 +/- 3.85 s) condition was faster than 10ACT (65.49 +/- 4.63 s) and PAS (65.89 +/- 4.55 s) conditions (P < .05). Blood lactate during the 15-min recovery period between the 100-m efforts was lower in both active recovery conditions compared with passive recovery (P < .05). Heart rate was higher during the 5ACT and 10ACT conditions compared with PAS during the 15-min recovery period (P < .05).

CONCLUSION

Five minutes of active recovery during a 15-min interval period is adequate to facilitate blood lactate removal and enhance performance in swimmers. Passive recovery and/or 10 min of active recovery is not recommended.

Effect of short recovery intensities on the performance during two Wingate tests

PURPOSE

To assess the effects of the intensity of short recoveries on performance by a Wingate test and on the deoxyhemoglobin variations.

METHODS

Twelve male subjects performed a graded test and three sessions of repeated all-out tests with different recovery natures. The repeated all-out tests included two sprints: a 15-s Wingate test followed by a 30-s Wingate test. The recovery between the two was 15 s in duration and was either passive, active at 20% of maximal aerobic power, or active at 40% of maximal aerobic power. Changes in deoxyhemoglobin were measured using by the near-infrared spectroscopy technique.

RESULTS

Mean power (517 +/- 26 W) and peak power (1085 +/- 153 W) of the 30-s Wingate test performed after passive recovery were significantly higher (P < 0.05) than mean power and peak power performed after active recovery at 20% (484 +/- 30 and 973 +/- 112 W, respectively) and 40% of maximal aerobic power (492 +/- 35 and 928 +/- 116 W, respectively). Deoxyhemoglobin variations were significantly higher (P < 0.05) during the passive recovery (12.8 +/- 5.3 microM) than during the active recovery conditions at 20% (4.3 +/- 2.6 microM) and 40% of maximal aerobic power (3.9 +/- 2.6 microM).

CONCLUSION

These results demonstrate that when two Wingate tests are performed almost successively but with a short recovery between the two, passive recovery is more appropriate than active recovery to restore the performance level.

Effect of different intensities of active recovery on sprint swimming performance

Active recovery reduces blood lactate concentration faster than passive recovery and, when the proper intensity is applied, a positive effect on performance is expected. The purpose of the study was to investigate the effect of different intensities of active recovery on performance during repeated sprint swimming. Nine male well-trained swimmers performed 8 repetitions of 25 m sprints (8 x 25 m) interspersed with 45 s intervals, followed by a 50 m sprint test 6 min later. During the 45 s and 6 min interval periods, swimmers either rested passively (PAS) or swam at an intensity corresponding to 50% (ACT50) and 60% (ACT60) of their individual 100 m velocity. Blood lactate was higher during PAS compared with ACT50 and ACT60 trials (p < 0.05), whereas plasma ammonia and glycerol concentration were not different between trials (p > 0.05). Mean performance time for the 8 x 25 m sprints was better in the PAS compared with the ACT50 and ACT60 trials (PAS: 13.10 +/- 0.07 vs. ACT50: 13.43 +/- 0.10 and ACT60: 13.47 +/- 0.10s, p < 0.05). The first 25 m sprint was not different across trials (p > 0.05), but performance decreased after sprint 2 during active recovery trials (ACT50 and ACT60) compared with the passive recovery (PAS) trial (p < 0.05). Performance time for the 50 m sprint performed 6 min after the 8 x 25 m sprints was no different between trials (p > 0.05). These results indicate that active recovery at intensities corresponding to 50% and 60% of the 100 m velocity during repeated swimming sprints decreases performance. Active recovery reduces blood lactate concentration, but does not affect performance on a 50 m sprint when 6 min recovery is provided. Passive recovery is advised during short-interval repeated sprint training in well-trained swimmers.

Effects of recovery mode on performance, O2 uptake, and O2 deficit during high-intensity intermittent exercise

The aim of this study was to determine the influence of activity performed during the recovery period on the aerobic and anaerobic energy yield, as well as on performance, during high-intensity intermittent exercise (HIT). Ten physical education students participated in the study. First they underwent an incremental exercise test to assess their maximal power output (Wmax) and VO2max. On subsequent days they performed three different HITs. Each HIT consisted of four cycling bouts until exhaustion at 110% Wmax. Recovery periods of 5 min were allowed between bouts. HITs differed in the kind of activity performed during the recovery periods: pedaling at 20% VO2max (HITA), stretching exercises, or lying supine. Performance was 3-4% and aerobic energy yield was 6-8% (both p < 0.05) higher during the HITA than during the other two kinds of HIT. The greater contribution of aerobic metabolism to the energy yield during the high-intensity exercise bouts with active recovery was due to faster VO2 kinetics (p< 0.01) and a higher VO2peak during the exercise bouts preceded by active recovery (p < 0.05). In contrast, the anaerobic energy yield (oxygen deficit and peak blood lactate concentrations) was similar in all HITs. Therefore, this study shows that active recovery facilitates performance by increasing aerobic contribution to the whole energy yield turnover during high-intensity intermittent exercise.

Continuous Muscle Stretch Prevents Disuse Muscle Atrophy and Deterioration of Its Oxidative Capacity in Rat Tail–Suspension Models

OBJECTIVE

The purpose of this study was to evaluate the effect of continuous muscle stretch on disuse-atrophied muscles.

DESIGN

Sprague-Dawley rats were used and divided into five groups: control group, hind limb suspended for 3 and 7 days, and hind-limb suspension plus strenuous continuous muscle stretch for 3 and 7 days. In the hind-limb suspension plus strenuous continuous muscle stretch groups, the gastrocnemius-plantaris-soleus muscles were stretched using a plastic plate that immobilized the ankle joint at the maximum dorsal flexed position during the hind-limb suspension period. The intracellular energy metabolism of the working muscle during electric stimulation was evaluated by phosphorus-31 magnetic resonance spectroscopy in vivo. Changes in phosphocreatine, inorganic phosphate, and the intracellular pH were monitored to evaluate intramuscular oxidative capacity. Maximum tension and muscle wet mass were also measured.

RESULTS

The oxidative capacity, muscle wet weight, and maximum tension decreased after hind-limb suspension. The muscle oxidative capacity at control levels was maintained during the first 3 days in muscles subjected to continuous strenuous stretch. It was also effective to prevent the decrease in muscle mass and maximum twitch tension during the initial 3 days. However, the effects did not persist.

CONCLUSION

Continuous strenuous stretch was effective to prevent disuse muscle atrophy and its functional deterioration; however, its effects did not last long.

High-energy phosphate metabolism during two bouts of progressive calf exercise in humans measured by phosphorus-31 magnetic resonance spectroscopy

According to the literature the steady-state level of phosphocreatine (PCr) has a linear relationship to the workload during muscle exercise intensities below the lactate threshold, whereas this linearity is impaired during exercise intensities above the lactate threshold. The purpose of this study was to investigate the linearity between PCr kinetics and workload during two bouts of isotonic incremental calf exercise with transitions from moderate- to high-intensity as well as from high- to moderate-intensity work rates. Using a whole-body 1.5 T MR scanner and a self-built exercise bench, we performed serial phosphorus-31 magnetic resonance spectroscopy ((31)P-MRS) with a time resolution of 30 s in nine healthy male volunteers. Changes in PCr, inorganic phosphate (Pi) and pH were statistically evaluated in comparison to the baseline. The exercise protocol started with a 4.5 W interval of 6 min followed by two bouts of 1.5 W increments. The workload was increased in 2-min intervals up to 9 W during the first bout and up to 7.5 W during the second bout. The second bout was preceded by a 4.5 W interval of 2 min and followed by a 4.5 W interval of 4 min. PCr hydrolysis achieved a steady state during each increment and was highly linear to the work rate (r (2), -0.796; P <0.001). Pi accumulated during each bout, whereas the pH decreased continuously during the first bout and did not exhibit any substantial decrease during the second bout. The metabolite levels and pH were expressed as the median value and the range. Our study confirms that steady-state PCr levels also have a linear relationship to work intensities above the lactate threshold, while pH changes do not have any impact on PCr degradation. The lack of substantial changes in pH during the second exercise bout indicates that prior high-intensity exercise leads to an activation of oxidative phosphorylation.