Background. Criteria are used to identify whether a subject has elicited a

We examined the effects of a 12-week program of Nordic hamstring exercises (NHE), administered before or after football training, upon eccentric hamstring strength, muscle activity, and architectural adaptations. Amateur soccer players were randomized into three groups. The control group (CON; n=11) undertook core stability exercises, whereas a periodized NHE program was delivered either before (NHE ; n=10) or after (NHE ; n=14) biweekly training sessions. Outcome measures included peak torque and concomitant normalized peak surface electromyography signals (sEMG) of the biceps femoris (BF) and medial hamstring (MH) muscles during knee flexor maximal eccentric contractions, performed at 30°·s . Ultrasonography was used to determine BF muscle thickness, muscle fiber pennation angle, and fascicle length. Performing the NHE derived likely moderate peak torque increases in both NHE (+11.9%; 90% confidence interval: 3.6%-20.9%) and NHE (+11.6%; 2.6%-21.5%) vs CON. Maximum sEMG increases were moderately greater in the BF of both NHE training groups vs CON. There were likely moderate increases in BF muscle thickness (+0.17 cm; 0.05-0.29 cm) and likely small pennation angle increases (+1.03°; -0.08° to 2.14°) in NHE vs CON and NHE . BF fascicle length increases were likely greater in NHE (+1.58 cm; 0.48-2.68 cm; small effect) vs CON and NHE . A 12-week eccentric hamstring strengthening program increased strength and sEMG to a similar magnitude irrespective of its scheduling relative to the football training session. However, architectural adaptations to support the strength gains differed according to the timing of the injury prevention program.

Athletes use many different strategies to enhance their performance, including clothing and footwear, training regimes, diets, and ergogenic aids. The use of ergogenic aids is believed to be widespread, with a variety of legal as well as illegal substances being used previously and currently. Among the more popular ergogenic aids is the use of sodium bicarbonate or sodium citrate, collectively recognized as "buffers." These substances potentially provide the body with added resistance against fatigue caused by deleterious changes in acid-base balance brought about by a variety of exercise modes and durations. The popularity of buffering has generated a plethora of research dating back to the 1930s, which continues to date. The issues surrounding buffering revolve around the dosage size, timing of ingestion, and the type of exercise to benefit from the use of buffers. We hope this review addresses these pertinent issues.

word count 253Text-only word count: 2904 Tables: 3 2 Abstract Objective: To investigate the application of differential ratings of perceived exertion for the examination of internal load during Australian Football League (AFL) matches. Number of references: 30 Number of Figures: 0 Number ofDesign: Single cohort, observational study. Methods:Using the centiMax rating of perceived exertion (RPE) scale, 26 professional AFL players provided ratings for match exertion (RPE-M), along with differential ratings for breathlessness (RPE-B), leg exertion (RPE-L), and technical demand (RPE-T) following 129 matches (5.0 ± 1.6 matches per player). Global positioning satellite (GPS) and accelerometer measures were also collected. Data were analysed using magnitude-based inferences.Results: RPE scores were 93.0  8.2 AU (RPE-M), 89.0  11.0 AU (RPE-B), 91.5  9.8 AU (RPE-L), and 87.0  10.0 AU (RPE-T). There was a most likely small difference between RPE-L and RPE-T (5.5%; 90% confidence limits 1.9%), a likely small difference between RPE-L and RPE-B (3.5%;1.5%) and a possibly small difference between RPE-B and RPE-T (1.9%; 1.9%). Within-player correlations between RPE and GPS measures were small for RPE-M (r=0.14-0.28), unclear to small for RPE-B (r=0.06-0.24) and unclear to moderate for RPE-L (r=0.06-0.37). Differential RPE's combined to explain 76% of the variance in RPE-M. For all RPE scores, within-player variability was moderate-high (typical error: 7.9-12.4%), and the thresholds for a likely between-match change were 8.8-13.7%. Conclusions:As differential RPE's represent distinct sensory inputs, the collection of these scores facilitate the interpretation of internal match loads and therefore represent a valuable addition to match data collection procedures. Moderate to high within-player variability should be considered when interpreting between-match changes in all RPE scores.

PurposeTo examine changes in hamstring muscle fatigue and central motor output during a 90-minute simulated soccer match, and the concomitant changes in hamstring maximal torque and rate of torque development.MethodEight amateur male soccer players performed a 90-minute simulated soccer match, with measures performed at the start of and every 15-minutes during each half. Maximal torque (Nm) and rate of torque development (RTD; Nm.s–1) were calculated from maximal isometric knee flexor contractions performed at 10° of flexion. Hamstring peripheral fatigue was assessed from changes in the size and shape of the resting twitch (RT). Hamstring central motor output was quantified from voluntary activation (%) and normalized biceps femoris (BF) and medial hamstrings (MH) electromyographic amplitudes (EMG/M).ResultsMaximal torque was reduced at 45-minutes by 7.6±9.4% (p<0.05). RTD in time intervals of 0–25, 0–50, and 0–75 ms post-contraction onset were reduced after 15-minutes in the first-half between 29.6 to 46.2% (p<0.05), and were further reduced at the end of the second-half (p<0.05). Maximal EMG/M was reduced for biceps femoris only concomitant to the time-course of reductions in maximal torque (p = 0.007). The rate of EMG rise for BF and MH was reduced in early time periods (0–75 ms) post-contraction onset (p<0.05). No changes were observed for the size and shape of the RT, indicating no hamstring peripheral fatigue.ConclusionCentrally mediated reductions in maximal torque and rate of torque development provide insight into factors that may explain hamstring injury risk during soccer. Of particular interest were early reductions during the first-half of hamstring rate of torque development, and the decline in maximal EMG/M of biceps femoris in the latter stages of the half. These are important findings that may help explain why the hamstrings are particularly vulnerable to strain injury during soccer.

Context: Epidemiologic findings of higher incidences of hamstrings muscle strains during the latter stages of soccer match play have been attributed to fatigue.Objective: To investigate the influence of soccer-specific fatigue on the peak eccentric torque of the knee flexor muscles.Design: Descriptive laboratory study. Results: Peak eccentric knee flexor torque at the end of the game (T 300eccH105 5 127 6 25 Nm) and at the end of the passive halftime interval (T 300eccH60 5 133 6 32 Nm) was reduced relative to T 300eccH00 (167 6 35 Nm, P , .01) and T 300eccH15 (161 6 35 Nm, P 5 .02).Conclusions: Eccentric hamstrings strength decreased as a function of time and after the halftime interval. This finding indicates a greater risk of injuries at these specific times, especially for explosive movements, in accordance with epidemiologic observations. Incorporating eccentric knee flexor exercises into resistance training sessions that follow soccerspecific conditioning is warranted to try to reduce the incidence or recurrence of hamstrings strains.Key Words: athletic injuries, isokinetic activity Key PointsN Eccentric peak hamstrings torque decreased during the match and after halftime. N The fatigued player may be more susceptible to both muscle strain and joint injuries. N Developing fatigue-resistant eccentric hamstrings strength and rewarming properly may help to reduce the risk of injury.H amstrings muscle strains are frequent injuries in professional soccer players. [1][2][3][4] In an epidemiologic study of English professional soccer athletes, the thigh was the most prevalent site for injury, with 81% of thigh injuries classified as muscular strains. 2 In US Major League Soccer, hamstrings strains incurred during matches and training sessions accounted for 42% of all strain injuries. 4 An etiologic risk factor commonly attributed to the high incidence of thigh strain injuries is poor eccentric muscular strength. 5,6 The temporal pattern of injury during match play also indicates that fatigue might be a factor. 2 In English professional soccer players, 47% of match-play hamstrings strains were incurred during the final 15 minutes of each half. 3 The fatigue associated with soccer match play is specific to the characteristic activity profile. Soccer has an irregular and intermittent activity profile 7-10 and, thus, when considering soccer-specific fatigue, we should account for both physiologic and mechanical load. A soccer-specific fatigue protocol, based on the activity profile of match play, 7,11 has been previously evaluated 12 based on the duration of exercise bouts and, therefore, the frequency of changes in speed. This effort contrasted with previous attempts to replicate the demands of soccer using treadmill or free-running protocols, which have only been evaluated against the physiologic response. 13,14 Our aim was to quantify the temporal influence of soccer-specific fatigue on changes in peak eccentric isokinetic torque of the knee flexors. If eccentric hamstrings strength is impaired as a result of fati...

While in vitro work has revealed that dehydration and hyperthermia can elicit increased cellular and oxidative stress, in vivo research linking dehydration, hyperthermia, and oxidative stress is limited. The purpose of this study was to investigate the effects of exercise-induced dehydration with and without hyperthermia on oxidative stress. Seven healthy male, trained cyclists (power output (W) at lactate threshold (LT): 199 ± 19 W) completed 90 min of cycling exercise at 95% LT followed by a 5-km time trial (TT) in 4 trials: (i) euhydration in a warm environment (EU-W, control), (ii) dehydration in a warm environment (DE-W), (iii) euhydration in a thermoneutral environment (EU-T), and (iv) dehydration in a thermoneutral environment (DE-T) (W: 33.9 ± 0.9 °C; T: 23.0 ± 1.0 °C). Oxidized glutathione (GSSG) increased significantly postexercise in dehydration trials only (DE-W: p < 0.01, DE-T: p = 0.03), and while not significant, total glutathione (TGSH) and thiobarbituric acid reactive substances (TBARS) tended to increase postexercise in dehydration trials (p = 0.08 for both). Monocyte heat shock protein 72 (HSP72) concentration was increased (p = 0.01) while lymphocyte HSP32 concentration was decreased for all trials (p = 0.02). Exercise-induced dehydration led to an increase in GSSG concentration while maintenance of euhydration attenuated these increases regardless of environmental condition. Additionally, we found evidence of increased cellular stress (measured via HSP) during all trials independent of hydration status and environment. Finally, both 90-min and 5-km TT performances were reduced during only the DE-W trial, likely a result of combined cellular stress, hyperthermia, and dehydration. These findings highlight the importance of fluid consumption during exercise to attenuate thermal and oxidative stress during prolonged exercise in the heat.

Boxing is a sport that consists of multiple high-intensity bouts separated by minimal recovery time and may benefit from a pre-exercise alkalotic state. The purpose of this study was to observe the ergogenic potential of sodium bicarbonate (NaHCO3) ingestion on boxing performance. Ten amateur boxers volunteered to participate in 2 competitive sparring bouts. The boxers were prematched for weight and boxing ability and consumed either 0.3 g.kg(-1) body weight (BW) of NaHCO3 (BICARB) or 0.045 g.kg(-1) BW of NaCl placebo (PLAC) mixed in diluted low calorie-flavored cordial. The sparring bouts consisted of four 3-minute rounds, each separated by 1-minute seated recovery. Blood acid-base (pH, bicarbonate [HCO3(-)], base excess [BE]), and performance (rates of perceived exertion [RPE], heart rate [HR] [HR(ave) and HR(max)], total punches landed successfully) profiles were analyzed before (where applicable) and after sparring. The results indicated a significant interaction effect for HCO3(-) (p < or = 0.001) and BE (p < 0.001), but not for pH (p = 0.48). Post hoc analysis revealed higher presparring HCO3(-) and BE for the BICARB condition, but no differences between the BICARB and PLAC conditions postsparring. There was a significant increase in punches landed during the BICARB condition (p < 0.001); however, no significant interaction effects for HRave (p = 0.15), HRmax (p = 0.32), or RPE (p = 0.38). The metabolic alkalosis induced by the NaHCO3 loading elevated before and after sparring blood buffering capacity. In practical application, the findings suggest that a standard NaHCO3 loading dose (0.3 g.kg(-1)) improves punch efficacy during 4 rounds of sparring performance.