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Jeffrey J. Dueweke, Tariq M. Awan and Christopher L. Mendias

Eccentric-contraction-induced skeletal muscle injuries, included in what is clinically referred to as muscle strains, are among the most common injuries treated in the sports medicine setting. Although patients with mild injuries often fully recover to their preinjury levels, patients who suffer moderate or severe injuries can have a persistent weakness and loss of function that is refractory to rehabilitation exercises and currently available therapeutic interventions. The objectives of this review were to describe the fundamental biophysics of force transmission in muscle and the mechanism of muscle-strain injuries, as well as the cellular and molecular processes that underlie the repair and regeneration of injured muscle tissue. The review also summarizes how commonly used therapeutic modalities affect muscle regeneration and opportunities to further improve our treatment of skeletal muscle strain injuries.

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Tessa Gordon, Esther Udina, Valerie M.K. Verge and Elena I. Posse de Chaves

Injured peripheral but not central nerves regenerate their axons but functional recovery is often poor. We demonstrate that prolonged periods of axon separation from targets and Schwann cell denervation eliminate regenerative capacity in the peripheral nervous system (PNS). A substantial delay of 4 weeks for all regenerating axons to cross a site of repair of sectioned nerve contributes to the long period of separation. Findings that 1h 20Hz bipolar electrical stimulation accelerates axon outgrowth across the repair site and the downstream reinnervation of denervated muscles in rats and human patients, provides a new and exciting method to improve functional recovery after nerve injuries. Drugs that elevate neuronal cAMP and activate PKA promote axon outgrowth in vivo and in vitro, mimicking the electrical stimulation effect. Rapid expression of neurotrophic factors and their receptors and then of growth associated proteins thereafter via cAMP, is the likely mechanism by which electrical stimulation accelerates axon outgrowth from the site of injury in both peripheral and central nervous systems.

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Sarah Kölling, Rob Duffield, Daniel Erlacher, Ranel Venter and Shona L. Halson

example, the high physical and mental stress imposed as part of normal athlete training and competition routines requires appropriate recovery time to facilitate adaptive processes. Given the role of sleep in metabolic, hormonal, and cognitive regeneration from daily activities when awake, 2 , 3

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Nicole McBrier and Jennifer A. Olczak

Edited by Michael G. Dolan

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Daniel Hammes, Sabrina Skorski, Sascha Schwindling, Alexander Ferrauti, Mark Pfeiffer, Michael Kellmann and Tim Meyer

The Lamberts and Lambert Submaximal Cycle Test (LSCT) is a novel test designed to monitor performance and fatigue/recovery in cyclists. Studies have shown the ability to predict performance; however, there is a lack of studies concerning monitoring of fatigue/recovery. In this study, 23 trained male cyclists (age 29 ± 8 y, VO2max 59.4 ± 7.4 mL · min−1 · kg−1) completed a training camp. The LSCT was conducted on days 1, 8, and 11. After day 1, an intensive 6-day training period was performed. Between days 8 and 11, a recovery period was realized. The LSCT consists of 3 stages with fixed heart rates of 6 min at 60% and 80% and 3 min at 90% of maximum heart rate. During the stages, power output and rating of perceived exertion (RPE) were determined. Heart-rate recovery was measured after stage 3. Power output almost certainly (standardized mean difference: 1.0) and RPE very likely (1.7) increased from day 1 to day 8 at stage 2. Power output likely (0.4) and RPE almost certainly (2.6) increased at stage 3. From day 8 to day 11, power output possibly (–0.4) and RPE likely (–1.5) decreased at stage 2 and possibly (–0.1) and almost certainly (–1.9) at stage 3. Heart-rate recovery was likely (0.7) accelerated from day 1 to day 8. Changes from day 8 to day 11 were unclear (–0.1). The LSCT can be used for monitoring fatigue and recovery, since parameters were responsive to a fatiguing training and a following recovery period. However, consideration of multiple LSCT variables is required to interpret the results correctly.

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Wigand Poppendieck, Oliver Faude, Melissa Wegmann and Tim Meyer

Purpose:

Cooling after exercise has been investigated as a method to improve recovery during intensive training or competition periods. As many studies have included untrained subjects, the transfer of those results to trained athletes is questionable.

Methods:

Therefore, the authors conducted a literature search and located 21 peer-reviewed randomized controlled trials addressing the effects of cooling on performance recovery in trained athletes.

Results:

For all studies, the effect of cooling on performance was determined and effect sizes (Hedges’ g) were calculated. Regarding performance measurement, the largest average effect size was found for sprint performance (2.6%, g = 0.69), while for endurance parameters (2.6%, g = 0.19), jump (3.0%, g = 0.15), and strength (1.8%, g = 0.10), effect sizes were smaller. The effects were most pronounced when performance was evaluated 96 h after exercise (4.3%, g = 1.03). Regarding the exercise used to induce fatigue, effects after endurance training (2.4%, g = 0.35) were larger than after strength-based exercise (2.4%, g = 0.11). Cold-water immersion (2.9%, g = 0.34) and cryogenic chambers (3.8%, g = 0.25) seem to be more beneficial with respect to performance than cooling packs (−1.4%, g= −0.07). For cold-water application, whole-body immersion (5.1%, g = 0.62) was significantly more effective than immersing only the legs or arms (1.1%, g = 0.10).

Conclusions:

In summary, the average effects of cooling on recovery of trained athletes were rather small (2.4%, g = 0.28). However, under appropriate conditions (whole-body cooling, recovery from sprint exercise), postexercise cooling seems to have positive effects that are large enough to be relevant for competitive athletes.

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Hugh H.K. Fullagar, Andrew Govus, James Hanisch and Andrew Murray

Purpose:

To investigate the recovery time course of customized wellness markers (sleep, soreness, energy, and overall wellness) in response to match play in American Division I-A college football players.

Methods:

A retrospective research design was used. Wellness data were collected and analyzed for 2 American college football seasons. Perceptions of soreness, sleep, energy, and overall wellness were obtained for the day before each game (GD–1) and the days after each game (GD+2, GD+3, and GD+4). Standardized effect-size (ES) analyses ± 90% confidence intervals were used to interpret the magnitude of the mean differences between all time points for the start, middle, and finish of the season, using the following qualitative descriptors: 0–0.19 trivial, 0.2–0.59 small, 0.6–1.19 moderate, 1.2–1.99 large, <2.0 very large.

Results:

Overall wellness showed small ES reductions on GD+2 (d = 0.22 ± 0.09, likely [94.8%]), GD+3 (d = 0.37 ± 0.15, very likely), and GD+4 (d = 0.29 ± 0.12, very likely) compared with GD–1. There were small ES reductions for soreness between GD–1 and GD+2, GD+3, and GD +4 (d = 0.21 ± 0.09, likely, d = 0.29 ± 0.12, very likely, and 0.30 ± 0.12, very likely, respectively). Small ES reductions were also evident between GD–1 and GD+3 (d = 0.21 ± 0.09, likely) for sleep. Feelings of energy showed small ESs on GD+3 (d = 0.27 ± 0.11, very likely) and GD+4 (d = 0.22 ± 0.09, likely) compared with GD–1.

Conclusion:

All wellness markers were likely to very likely worse on GD+3 and GD+4 than on GD–1. These findings show that perceptual wellness takes longer than 4 d to return to pregame levels and thus should be considered when prescribing training and/or recovery.

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Elizaveta Kon, Matej Drobnic, Phil A. Davidson, Andrew Levy, Ken Zaslav and Dror Robinson

Osteochondral defects are often symptomatic and lead to deranged joint function. The spontaneous healing capacity of osteochondral defects is limited. In this case study, use of an acellular scaffold capable of induction of mesenchymal stem-cell migration is described. This scaffold was used on an Outerbridge grade IV medical condylar defect measuring ~2 cm2. At 24 mo follow-up, the articular surface appeared restored by MRI, and the patient returned to sports.

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Hugh H.K. Fullagar, Rob Duffield, Sabrina Skorski, Aaron J. Coutts, Ross Julian and Tim Meyer

While the effects of sleep loss on performance have previously been reviewed, the effects of disturbed sleep on recovery after exercise are less reported. Specifically, the interaction between sleep and physiological and psychological recovery in team-sport athletes is not well understood. Accordingly, the aim of the current review was to examine the current evidence on the potential role sleep may play in postexercise recovery, with a tailored focus on professional team-sport athletes. Recent studies show that team-sport athletes are at high risk of poor sleep during and after competition. Although limited published data are available, these athletes also appear particularly susceptible to reductions in both sleep quality and sleep duration after night competition and periods of heavy training. However, studies examining the relationship between sleep and recovery in such situations are lacking. Indeed, further observational sleep studies in team-sport athletes are required to confirm these concerns. Naps, sleep extension, and sleep-hygiene practices appear advantageous to performance; however, future proof-of-concept studies are now required to determine the efficacy of these interventions on postexercise recovery. Moreover, more research is required to understand how sleep interacts with numerous recovery responses in team-sport environments. This is pertinent given the regularity with which these teams encounter challenging scenarios during the course of a season. Therefore, this review examines the factors that compromise sleep during a season and after competition and discusses strategies that may help improve sleep in team-sport athletes.

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Hugh H.K. Fullagar, Rob Duffield, Sabrina Skorski, David White, Jonathan Bloomfield, Sarah Kölling and Tim Meyer

Purpose:

The current study examined the sleep, travel, and recovery responses of elite footballers during and after long-haul international air travel, with a further description of these responses over the ensuing competitive tour (including 2 matches).

Methods:

In an observational design, 15 elite male football players undertook 18 h of predominantly westward international air travel from the United Kingdom to South America (–4-h time-zone shift) for a 10-d tour. Objective sleep parameters, external and internal training loads, subjective player match performance, technical match data, and perceptual jet-lag and recovery measures were collected.

Results:

Significant differences were evident between outbound travel and recovery night 1 (night of arrival; P < .001) for sleep duration. Sleep efficiency was also significantly reduced during outbound travel compared with recovery nights 1 (P = .001) and 2 (P = .004). Furthermore, both match nights (5 and 10), showed significantly less sleep than nonmatch nights 2 to 4 and 7 to 9 (all P < .001). No significant differences were evident between baseline and any time point for all perceptual measures of jet-lag and recovery (P > .05), although large effects were evident for jet-lag on d 2 (2 d after arrival).

Conclusions:

Sleep duration is truncated during long-haul international travel with a 4-h time-zone delay and after night matches in elite footballers. However, this lost sleep appeared to have a limited effect on perceptual recovery, which may be explained by a westbound flight and a relatively small change in time zones, in addition to the significant increase in sleep duration on the night of arrival after the long-haul flight.