Stephen H. Day

Exercise-induced skeletal muscle damage and adaptation following repeated bouts of eccentric muscle contractions

Repeated bouts of eccentric muscle contractions were used to examine indirect indices of exercise-induced muscle damage and adaptation in human skeletal muscle. Twenty-four subjects (18 females, 6 males) aged 20.0 +/- 1.4 years (mean +/- S.D.) performed an initial bout of either 10 (n = 7), 30 (n = 9) or 50 (n = 8) maximum voluntary eccentric contractions of the knee extensors, followed by a second bout of 50 contractions 3 weeks later using the same leg. Muscle soreness was elevated after all bouts (P < 0.05, Wilcoxon test), although the initial bout reduced the soreness associated with the second bout. Force loss and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio were observed after all exercise bouts (P < 0.01). Serum creatine kinase activity was elevated following the initial bouts of 30 and 50 repetitions (P < 0.01), but there was no increase following 10 repetitions. No increase in serum creatine kinase activity was observed in any group following the second bout of contractions (P > 0.05). We conclude that skeletal muscle adaptation can be brought about by a single bout of relatively few eccentric muscle contractions. Increasing the number of eccentric muscle repetitions did not result in an increased prophylactic effect on skeletal muscle.

Indices of skeletal muscle damage and connective tissue breakdown following eccentric muscle contractions

Abstract Indirect indices of exercise-induced human skeletal muscle damage and connective tissue breakdown were studied following a single bout of voluntary eccentric muscle contractions. Subjects (six female, two male), mean (SD) age 22 (2) years performed a bout of 50 maximum voluntary eccentric contractions of the knee extensors of a single leg. The eccentric exercise protocol induced muscle soreness (P < 0.05 Wilcoxon test), chronic force loss, and a decline in the 20:100 Hz percutaneous electrical myostimulation force ratio [P < 0.01, repeated measures analysis of variance (ANOVA)]. Serum creatine kinase (CK) and lactate dehydrogenase (LDH) activities were elevated (P < 0.01, repeated measures ANOVA) following the bout. The mean (SD) CK and LDH levels recorded 3 days post-exercise were 2815 (4144) IU · l–1 and 375 (198) IU · l–1, respectively. Serum alkaline phosphatase activity showed no changes throughout the study, and a non-significant increase (P = 0.058, repeated measures ANOVA) in pyridinoline was recorded following the bout. Urinary hydroxyproline (HP) and hydroxylysine (HL) excretion, expressed in terms of creatinine (Cr) concentration, increased after exercise (P < 0.05 and P < 0.01, respectively, repeated measures ANOVA). An increased HP:Cr was recorded 2 days post-exercise and HL:Cr was increased above baseline on days 2, 5, and 9 post-exercise. This indirect evidence of exercise-induced muscle damage suggests that myofibre disruption was caused by the eccentric muscle contractions. Elevated urine concentrations of indirect indices of collagen breakdown following eccentric muscle contractions suggests an increased breakdown of connective tissue, possibly due to a localised inflammatory response.

Indirect evidence of human skeletal muscle damage and collagen breakdown after eccentric muscle actions

Indirect markers of muscle damage and collagen breakdown were recorded for up to 9 days after a bout of concentric, followed by a bout of eccentric, muscle actions. Nine untrained participants performed two bouts of 50 maximum effort repetitions on an isokinetic dynamometer (angular velocity 1.05 rad x s(-1), range of motion 1.75 rad). An initial concentric bout of muscle actions was followed by an eccentric bout 21 days later, using the same knee extensors. Concentric actions induced no changes in maximum voluntary isometric contraction force (MVC), nor induced any changes in the serum enzyme activities of creatine kinase, a lactate dehydrogenase isoenzyme (LDH-1), or alkaline phosphatase. Similarly, concentric actions induced no change in markers of collagen breakdown, namely plasma hydroxyproline and serum type 1 collagen concentration. In contrast, eccentric actions induced a 23.5+/-19.0% (mean+/-s) decrease in MVC immediately post-exercise (P < 0.05), and increased the serum enzyme activities of creatine kinase and LDH-1 to 486+/-792 and 90+/-11 IU.l(-1) respectively on day 3 post-exercise, and to 189+/-159 and 96+/-13 IU x l(-1) respectively on day 7 post-exercise (all P< 0.05). Eccentric actions induced no significant changes in plasma hydroxyproline, but increased collagen concentration on days 1 and 9 post-exercise (48.6% and 44.3% increases above pre-exercise on days 1 and 9 respectively; both P < 0.05). We conclude that eccentric but not concentric actions may result in temporary muscle damage, and that collagen breakdown may also be affected by eccentric actions. With caution, indices of collagen breakdown may be used to identify exercise-induced damage to connective tissue.

Changes in human skeletal muscle contractile function following stimulated eccentric exercise.

Indices of human skeletal muscle contractile function were examined in nine subjects for up to 9 days following a single bout of stimulated eccentric exercise. Eccentric muscle actions of the knee extensor muscles were evoked by percutaneous electrical myostimulation (PES). Delayed onset muscle soreness (DOMS), elevated serum creatine kinase activity, chronic force loss, and a decline in the 20: 100 Hz force ratio were observed in the days postexercise. The exercised knee extensor muscles demonstrated an impaired ability to respond to PES. This was evident by an increased time delay between the start of 100 Hz PES and the onset of contraction immediately postexercise [22.3 (SD 15.9)%, P < 0.01] and 3 days postexercise [14.9 (SD 18.1)%, P < 0.05]. Muscle relaxation rates appeared unaffected by the eccentric exercise protocol, where the muscles showed no differences in the time between the end of PES and the onset of relaxation (P > 0.05). During the days following the exercise, no significant differences were observed in the time between the start of contraction and attainment of 70% of the mean tetanic force following a single 1-s pulse of PES. Similarly, no significant differences were observed in the time between the start of relaxation and attainment of 70% of the total relaxation during the same time. The increased delay in excitation-contraction coupling observed immediately postexercise and 3 days after the exercise, may reflect a damage-induced delay in action potential propagation. Muscle relaxation rates postexercise remained unchanged, which would seem to indicate normal functioning of the sarcoplasmic reticulum, suggesting this was not the site of failure in excitation-contraction coupling.

The effect of severe eccentric exercise-induced muscle damage on plasma elastase, glutamine and zinc concentrations.

Abstract The aim of this study was to determine if severe exercise-induced muscle damage alters the plasma concentrations of glutamine and zinc. Changes in plasma concentrations of glutamine, zinc and polymorphonuclear elastase (an index of phagocytic cell activation) were examined for up to 10 days following eccentric exercise of the knee extensors of one leg in eight untrained subjects. The exercise bout consisted of 20 repetitions of electrically stimulated eccentric muscle actions on an isokinetic dynamometer. Subjects experienced severe muscle soreness and large increases in plasma creatine kinase activity indicative of muscle fibre damage. Peak soreness occurred at 2 days post-exercise and peak creatine kinase activity [21714 (6416) U · l−1, mean (SEM)] occurred at 3 days post-exercise (P < 0.01 compared with pre-exercise). Plasma elastase concentration was increased at 3 days post-exercise compared with pre-exercise (P < 0.05), and is presumably indicative of ongoing phagocytic leucocyte infiltration and activation in the damaged muscles. There were no significant changes in plasma zinc and glutamine concentrations in the days following eccentric exercise. We conclude that exercise-induced muscle damage does not produce changes in plasma glutamine or zinc concentrations despite evidence of phagocytic neutrophil activation.

Genetics of muscle strength and power: Polygenic profile similarity limits skeletal muscle performance

Abstract Environmental and genetic factors influence muscle function, resulting in large variations in phenotype between individuals. Multiple genetic variants (polygenic in nature) are thought to influence exercise-related phenotypes, yet how the relevant polymorphisms combine to influence muscular strength in individuals and populations is unclear. In this analysis, 22 genetic polymorphisms were identified in the literature that have been associated with muscular strength and power phenotypes. Using typical genotype frequencies, the probability of any given individual possessing an “optimal” polygenic profile was calculated as 0.0003% for the world population. Future identification of additional polymorphisms associated with muscular strength phenotypes would most likely reduce that probability even further. To examine the genetic potential for muscular strength within a human population, a “total genotype score” was generated for each individual within a hypothetical population of one million. The population expressed high similarity in polygenic profile with no individual differing by more than seven genotypes from a typical profile. Therefore, skeletal muscle strength potential within humans appears to be limited by polygenic profile similarity. Future research should aim to replicate more genotype–phenotype associations for muscular strength, because only five common genetic polymorphisms identified to date have positive replicated findings.

Vibration training improves balance in unstable ankles.

Functional ankle instability (FAI) is a common condition following ankle injury characterised by increased risk of injury. Ankle sprains are a common acute form of injury suffered in dancing and loss of balance can affect not only risk of injury risk but also performance aesthetics. Whole body vibration training (WBVT) is a new rehabilitation method that has been linked with improving balance and muscle function. 38 female dancers with self reported unilateral FAI were randomly assigned in 2 groups: WBVT and control. Absolute centre of mass (COM) distribution during single leg stance, SEBT normalised research distances and Peroneus longus mean power frequency (f(med)) where measured pre and post 6-week intervention. There was a significant improvement in COM distribution over the 6 weeks from 1.05 ± 0.57 to 0.33 ± 0.42 cm² (P<0.05), and 4 of the 8 planes of direction in the SEBT Ant, Antlat, Med and Antmed from 77.5 ± 7.1 to 84.1 ± 5.8% (P<0.05) compared to control groups during the course of the 6 week training intervention. There was no evidence of improvement in peroneus longus (f(med)) over time (P=0.915) in either group. WBVT improved static balance and SEBT scores amongst dancers exhibiting ankle instability but did not affect peroneus longus muscle fatigue.

Whole-body efficiency is negatively correlated with minimum torque per duty cycle in trained cyclists

Abstract The purpose of this study was to determine whether there is a causal relationship between pedalling “circularity” and cycling efficiency. Eleven trained cyclists were studied during submaximal cycling. Variables recorded included gross and delta efficiency and the ratio of minimum to peak torque during a duty cycle. Participants also completed a questionnaire about their training history. The most notable results were as follows: gross efficiency (r = −0.72, P < 0.05 at 250 W) was inversely correlated with the ratio of minimum to peak torque, particularly at higher work rates. There was a highly significant inverse correlation between delta efficiency and average minimum torque at 200 W (r = −0.76, P < 0.01). Cycling experience was positively correlated with delta efficiency and gross efficiency, although experience and the ratio of minimum to peak torque were not related. These results show that variations in pedalling technique may account for a large proportion of the variation in efficiency in trained cyclists. However, it is also possible that some underlying physiological factor influences both. Finally, it appears that experience positively influences efficiency, although the mechanism by which this occurs remains unclear.

Electromyogram activity and mean power frequency in exercise‐damaged human muscle

Eight volunteers performed two bouts of 50 voluntary maximal eccentric contractions of the knee extensors of one leg 3 weeks apart. During maximal voluntary isometric contractions performed at intervals after each bout, electromyogram (EMG) mean power frequency declined after bout one (P < 0.01 Duncans test), whereas integrated EMG did not change after either bout. These results suggest that unaccustomed eccentric contractions produce a temporary reduction in mean muscle activation frequency during subsequent maximal isometric contractions.

Six-week combined vibration and wobble board training on balance and stability in footballers with functional ankle instability

Objective:To compare the effectiveness of a combination of vibration and wobble board training against wobble board training alone in footballers suffering from functional ankle instability (FAI). Design:A 2 × 3 prefactorial–postfactorial design. Setting:University research laboratory. Participants:Thirty-three male semiprofessional footballers with self-reported unilateral FAI were randomly assigned in 3 groups: vibration and wobble board (mean age 22.2 years), wobble board (mean age 22.7 years), and control (mean age 23.1 years). Interventions:Participants in each intervention group performed a 6-week progressive rehabilitation program using a wobble board, either with or without the addition of vibration stimulus. Main Outcome Measures:Absolute center of mass (COM) distribution during single-leg stance, modified star excursion balance test (SEBT) reach distances, and single-leg triple hop for distance (SLTHD) were measured before and after 6-week intervention. Results:Combined vibration and wobble board training resulted in reduced COM distribution [P ⩽ 0.001, effect size (ES) = 0.66], increased SEBT reach distances (P ⩽ 0.01 and P ⩽ 0.002, ES = 0.19 and 0.29, respectively), and increased SLTHD (P ⩽ 0.001, ES = 0.33) compared with wobble board training alone during the course of the 6-week training intervention. Conclusions:Combined vibration and wobble board training improves COM distribution, modified SEBT scores, and SLTHD among footballers suffering FAI compared with wobble board training alone.