Jason C. Siegler

Soccer-Specific Fatigue and Eccentric Hamstrings Muscle Strength

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. SETTING Controlled laboratory environment. PATIENTS OR OTHER PARTICIPANTS Ten male professional soccer players (age = 24.7 +/- 4.4 years, mass = 77.1 +/- 8.3 kg, Vo(2max) = 63.0 +/- 4.8 mL x kg(-1) x min(-1)). INTERVENTION(S) Participants completed an intermittent treadmill protocol replicating the activity profile of soccer match play, with a passive halftime interval. Before exercise and at 15-minute intervals, each player completed isokinetic dynamometer trials. MAIN OUTCOME MEASURE(S) Peak eccentric knee flexor torque was quantified at isokinetic speeds of 180 degrees x s(-1), 300 degrees x s(-1), and 60 degrees x s(-1), with 5 repetitions at each speed. RESULTS Peak eccentric knee flexor torque at the end of the game (T(300eccH105) = 127 +/- 25 Nm) and at the end of the passive halftime interval (T(300eccH60) = 133 +/- 32 Nm) was reduced relative to T(300eccH00) (167 +/- 35 Nm, P < .01) and T(300eccH15) (161 +/- 35 Nm, P = .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 soccer-specific conditioning is warranted to try to reduce the incidence or recurrence of hamstrings strains.

Exercise-induced dehydration with and without environmental heat stress results in increased oxidative stress

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.

Practical Recommendations for Coaches and Athletes: A Meta-Analysis of Sodium Bicarbonate Use for Athletic Performance

Abstract Peart, DJ, Siegler, JC, and Vince, RV. Practical recommendations for coaches and athletes: A meta-analysis of sodium bicarbonate use for athletic performance. J Strength Cond Res 26(7): 1975–1983, 2012—Sodium bicarbonate (NaHCO3) is a buffering agent that is suggested to improve performance by promoting the efflux of hydrogen ions from working cells and tissues. Research surrounding its efficacy as an ergogenic aid is conflicting, making it difficult to draw conclusions as to its effectiveness for training and competition. This study performed a meta-analysis of relevant research articles to allow the development of concise practical recommendations for coaches and athletes. The overall effect size for the influence of NaHCO3 on performance was moderate, and was significantly lower for specifically trained as opposed to recreationally trained participants.

Sodium bicarbonate ingestion and boxing performance

Siegler, JC and Hirscher, K. Sodium bicarbonate ingestion and boxing performance. J Strength Cond Res 24(1): 103-108, 2010-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] [HRave and HRmax], total punches landed successfully) profiles were analyzed before (where applicable) and after sparring. The results indicated a significant interaction effect for HCO3− (p ≤ 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.

Effects of various sodium bicarbonate loading protocols on the time-dependent extracellular buffering profile.

Siegler, JC, Midgley, AW, Polman, RCJ, and Lever, R. Effects of various sodium bicarbonate loading protocols on the time-dependent extracellular buffering profile. J Strength Cond Res 24(9): 2551-2557, 2010-Although much research has investigated the types of exercise that are enhanced with sodium bicarbonate (NaHCO3) ingestion, to date, there has been limited research on the dosage and timing of ingestion that optimizes the associated ergogenic effects. This study investigated the effects of various NaHCO3 loading protocols on the time-dependent blood-buffering profile. Eight male volunteers (age, 22.4 ± 5.7 yr; height, 179.8 ± 9.6 cm, body mass, 76.3 ± 14.1 kg) completed Part A, measures of alkalosis throughout 120 minutes after ingestion of various single NaHCO3 dosages (0.3 g·kg−1, 0.2 g·kg−1, 0.1 g·kg−1, and placebo); and Part B, similar profiles after alternative NaHCO3 loading protocols (single morning dosage [SMD], single evening dosage [SED], and dosages ingested on 3 consecutive evenings [CED]). Results from Part A are as follows. Blood buffering in the 0.1 g·kg−1 condition was significantly lower than the 0.2 g·kg−1 and 0.3 g·kg−1 conditions (p < 0.002), but there was no significant differences between the 0.2 g·kg−1 and 0.3 g·kg−1 conditions (p = 0.34). Although the blood buffering was relatively constant in the 0.1 and 0.2 conditions, it was significantly higher at 60 minutes than at 100 minutes and 120 minutes in the 0.3 g·kg−1 condition (p < 0.05). Results from Part B are as follows. Blood buffering for SMD was significantly higher than for SED and CED (p < 0.05). Blood buffering in the SMD condition was significantly lower at 17:00 hours than at 11:00 hours (p = 0.007). The single 0.2 and 0.3 g·kg−1 NaHCO3 dosages appeared to be the most effective for increasing blood-buffering capacity. The 0.2 g·kg−1 dosage is best ingested 40 to 50 minutes before exercise and the 0.3 g·kg−1 dosage 60 minutes before exercise.

Hamstring Muscle Fatigue and Central Motor Output during a Simulated Soccer Match

Purpose To 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. Method Eight 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). Results Maximal 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. Conclusion Centrally 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.

The application of differential ratings of perceived exertion to Australian Football League matches

OBJECTIVES To investigate the application of differential ratings of perceived exertion for the examination of internal load during Australian Football League (AFL) matches. DESIGN 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 RPEs combined to explain 76% of the variance in RPE-M. For all RPE scores, within-player variability was moderate to high (typical error: 7.9-12.4%), and the thresholds for a likely between-match change were 8.8-13.7%. CONCLUSIONS As differential RPEs 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.

Acute neuromuscular and fatigue responses to the rest-pause method

OBJECTIVES To compare muscle recruitment, maximal force, and rate of force development changes following different resistance exercise protocols with a constant volume-load. DESIGN Within-subjects randomized crossover trial. METHODS Fourteen (n=14) resistance trained male participants completed three different resistance exercise protocols involving 20 squat repetitions, prescribed at 80% of 1-repetition-maximum. Protocol A consisted of 5 sets of 4 repetitions with 3 min inter-set rest intervals, protocol B was 5 sets of 4 repetitions with 20 s inter-set rest intervals, and the rest-pause method was an initial set to failure with subsequent sets performed with a 20 s inter-set rest interval. Maximal squat isometric force output and rate of force development (RFD) were measured before, immediately upon completion (IP), and 5 min (5P) following each protocol. Muscle activity from 6 different thigh and hip muscles was measured with surface electromyography (EMG) at each time point, and during every squat repetition. RESULTS Participants completed the rest-pause method in 2.1±0.4 sets, with a total protocol duration of 103 s compared to 140 s and 780 s for protocols B and A, respectively. All protocols elicited similar decreases (p<0.05) in maximal force and RFD at IP, with full recovery at 5P. Increased motor unit recruitment was observed during the rest-pause method compared to both protocols A and B for all muscles measured (p<0.05). CONCLUSIONS As a result of the increased EMG during exercise and no greater post-exercise fatigue, it was concluded that the rest-pause method may be an efficacious training method for resistance-trained individuals.

Sodium bicarbonate ingestion and repeated swim sprint performance

Siegler, JC and Gleadall-Siddall, D0. Sodium bicarbonate ingestion and repeated swim sprint performance. J Strength Cond Res 24(11): 3105-3111, 2010-The purpose of the present investigation was to observe the ergogenic potential of 0.3 g·kg−1 of sodium bicarbonate (NaHCO3) in competitive, nonelite swimmers using a repeated swim sprint design that eliminated the technical component of turning. Six male (181.2 ± 7.2 cm; 80.3 ± 11.9 kg; 50.8 ± 5.5 ml·kg−1·min−1 &OV0312;O2max) and 8 female (168.8 ± 5.6 cm; 75.3 ± 10.1 kg; 38.8 ± 2.6 ml·kg−1·min−1 &OV0312;O2max) swimmers completed 2 trial conditions (NaHCO3 [BICARB] and NaCl placebo [PLAC]) implemented in a randomized (counterbalanced), single blind manner, each separated by 1 week. Swimmers were paired according to ability and completed 8, 25-m front crawl maximal effort sprints each separated by 5 seconds. Blood acid-base status was assessed preingestion, pre, and postswim via capillary finger sticks, and total swim time was calculated as a performance measure. Total swim time was significantly decreased in the BICARB compared to PLAC condition (p = 0.04), with the BICARB condition resulting in a 2% decrease in total swim time compared to the PLAC condition (159.4 ± 25.4 vs. 163.2 ± 25.6 seconds; mean difference = 4.4 seconds; 95% confidence interval = 8.7-0.1). Blood analysis revealed significantly elevated blood buffering potential preswim (pH: BICARB = 7.48 ± 0.01, PLAC = 7.41 ± 0.01) along with a significant decrease in extracellular K+ (BICARB = 4.0 ± 0.1 mmol·L−1, PLAC = 4.6 ± 0.1 mmol·L−1). The findings suggest that 0.3 g·kg−1 NaHCO3 ingested 2.5 hours before exercise enhances the blood buffering potential and may positively influence swim performance.

Relative torque profiles of elite male youth footballers: effects of age and pubertal development

This study aimed to establish the effect of age and pubertal development on relative peak torque in youth footballers. One hundred and fifty-seven subjects were arranged into U12-U18 age groups; of these 133 also completed a self-reporting measure of pubertal development (PDS) and were grouped accordingly. Bilateral isokinetic testing included mean peak torque/body weight (PT/BW) and angle of peak torque (AoPT) for reps 2-4 of 5 in concentric quadriceps (CQ), concentric hamstrings (CH) and eccentric hamstrings (EH) at 60 degrees s(-1). Two minutes rest were provided between concentric and eccentric tests for both legs. A significant increase with age was noted for PT/BW in CQ, CH and EH (P<0.05), although POST HOC analyses revealed different patterns of significance dependent upon muscle and type of contraction. Specifically, the U18 s (CQ:2.20 nm/kg, CH:1.39 nm/kg, EH:2.16 nm/kg) were not significantly stronger than the U16 s and U15 s (CQ:2.42/2.29 nm/kg, CH:1.41/1.27 nm/kg, EH:2.22/2.15 nm/kg) even though they had entered full time training. The relationship between EH PT/BW and AoPT showed a weak but significant inverse correlation (P<0.001; R= -0.390 and -0.346 for dominant and non dominant legs). The findings of this study present unique football specific normative and age/PDS group data for PT/BW and AoPT, and the corresponding relationship between these variables.