Alan E. Donnelly

Neuromuscular dysfunction following eccentric exercise.

This study examined the effects of exercise-induced muscle damage on tremor and proprioception components of neuromuscular function. Six male and six female volunteers (aged 18-30 yr) performed 50 maximal eccentric muscle actions using the forearm flexors of the nondominant arm. Forearm flexor tremor and perception of voluntary force and joint position were monitored to assess changes in neuromuscular function. Data were analyzed using REANOVA. Serum creatine kinase activity increased from a baseline value of 68 +/- 13 IU.l-1 to 2849 +/- 852 IU.l-1 5 d after exercise (P < 0.05). This was accompanied by prolonged impaired joint range of motion (P < 0.01) and reduced maximum strength (P < 0.01). Muscle soreness peaked 3 d postexercise (P < 0.01; Wilcoxon test). Tremor amplitude was increased (P < 0.01) until 48 h after exercise, whereas the power frequency spectrum was unaffected. Perception of joint position at elbow angles of 1.57 rad (P < 0.01) and 2.09 rad (P < 0.05) and perception of force (P < 0.01) were significantly impaired when the control arm acted as the reference. Joint positions were more accurately reproduced when the experimental arm acted as its own reference. The increase in tremor amplitude and loss of proprioceptive function in the days after damage-inducing eccentric exercise suggest significant impairment of neuromuscular function.

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.

Elevated serum antioxidant capacity and plasma malondialdehyde concentration in response to a simulated half-marathon run

PURPOSE AND METHODS Indices of antioxidant status, membrane permeability, and lipid peroxidation were investigated in venous blood immediately before and after a simulated half-marathon run. In serum, these included the ability to scavenge free radicals (total antioxidant capacity, TAC), the concentration of uric acid (UA), and the activities of creatine kinase (CK) and beta-glucuronidase (beta G). The plasma concentration of malondialdehyde (MDA) was used as a marker of lipid peroxidation. Data were analyzed with paired t-tests. After a standardized warm-up, 17 trained male runners (mean +/- SD, age 31 +/- 4 yr, peak VO2 63.2 +/- 4.8 mL.kg-1.min-1) each completed a self-paced half-marathon run, on a motorized treadmill. Average exercise intensity was 77.1 +/- 1.0% peak VO2, with a performance time of 87.1 +/- 7.0 min. RESULTS After exercise, elevations were observed in MDA from 1.48 +/- 0.39 mmol.L-1 to 1.65 +/- 0.32 mmol.L-1 (P < 0.05), TAC from 475 +/- 84 to 564 +/- 113 mmol Trolox Eq.L-1 (P < 0.0001), UA from 268 +/- 45 to 312 +/- 51 mmol.L-1 (P < 0.001), serum cortisol concentration from 339 +/- 95 to 557 +/- 157 nmol.L-1 (P < 0.01), CK from 98 +/- 67 to 133 +/- 89 IU.L-1 (P < 0.0001), and beta G from 15.39 +/- 5.34 to 17.05 +/- 5.7 Sigma Units.mL-1 (P < 0.001). CONCLUSIONS The rise in TAC did not prevent exercise-induced lipid peroxidation and muscle damage as both MDA and CK were elevated after exercise. This may indicate inadequacies in the antioxidant defense system during the half-marathon run.

Indices of free-radical-mediated damage following maximum voluntary eccentric and concentric muscular work.

This study monitored plasma and skeletal muscle markers of free-radical-mediated damage following maximum eccentric and concentric exercise, to examine the potential role of free radicals in exercise-induced muscle damage. Fourteen male volunteers performed either (1) a bout of 70 maximum eccentric and a bout of 70 maximum concentric muscle actions of the forearm flexors (the bouts being separated by 4 weeks; n = 8) or (2) a bout of 80 maximum eccentric and a bout of 80 maximum concentric muscle actions of the knee extensors (the bouts being separated by 1 week; n=6). Plasma markers of lipid peroxidation, thiobarbituric acid-reactive substances (TBARS) and diene-conjugated compounds (DCC) were monitored in the arm protocol and skeletal muscle markers of oxidative lipid and protein damage, malondialdehyde (MDA) and protein carbonyl derivatives (PCD) respectively, were monitored in the leg protocol. In both protocols, the contralateral limb was used for the second bout and the order of the bouts was randomised between limbs. Repeated measures ANOVA indicated significant changes from baseline following eccentric arm work on the measures of serum creatine kinase activity (P < 0.05), maximum voluntary torque production (P < 0.01) and relaxed arm angle (P < 0.01). Subjective muscle soreness peaked 2 days after eccentric arm work (P < 0.05, Wilcoxon test). However, there were no changes in the plasma levels of TBARS or DCC following the eccentric or concentric arm exercise. Immediately after concentric leg exercise, skeletal muscle PCD concentrations was significantly higher than that observed immediately after eccentric work (P < 0.05). However, no significant difference between the eccentric and concentric knee extensor bouts was observed on the measure of skeletal muscle MDA concentration. The results of this study offer no support for the involvement of oxygen free radicals in exercise-induced muscle damage.

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.

Effects of ibuprofen on exercise-induced muscle soreness and indices of muscle damage.

Thirty-two volunteers participated in a two-period crossover study in which ibuprofen was tested against an identical placebo for its effectiveness in reducing muscle soreness and damage after two bouts of downhill running. Subjective soreness, quadriceps isometric strength and isometric endurance time at 50 percent of maximum strength, serum activities of creatine kinase, lactate dehydrogenase and aspartate transaminase and serum levels of creatinine and urea were recorded at intervals up to 72 hours after exercise. Each downhill run produced muscle soreness, and a decline in muscle strength and 50 percent endurance time, although these parameters were unaffected by ibuprofen treatment. All serum parameters measured increased after both runs, but for the three enzymes this increase was smaller after the second run. Serum creatine kinase and urea levels were higher in the ibuprofen group after both runs. These results indicate that ibuprofen is not an appropriate treatment for delayed onset muscle soreness and damage.

Comparison of eccentric knee extensor muscle actions at two muscle lengths on indices of damage and angle-specific force production in humans.

In this study, we investigated the effects of knee extensor length during eccentric exercise on indices of muscle damage and adaptation. Subjects (n = 7) performed two bouts of 75 maximal voluntary eccentric muscle actions at a knee joint angular velocity of 1.57 rad s(-1). One bout was performed at a short muscle length (bout S) with a knee joint range of motion of 2.79 to 1.40 radians (160 degrees to 80 degrees), and a second with the contralateral knee extensors at a long muscle length (bout L) with a range of motion of 2.01 to 0.7 radians (120 degrees to 40 degrees). The maximum voluntary contractile force (MVC) was measured before and 5 min after exercise, and again on days 3, 5, 7, 10 and 12, at knee angles of 160 degrees, 120 degrees and 80 degrees. Muscle soreness was measured before exercise and on each day after exercise. Serum creatine kinase activity was measured before exercise and on days 3, 5, 7, 10 and 12 post-exercise. The MVC declined after each bout (P < 0.01), with a greater decline after bout L (P < 0.05). Muscle soreness was higher relative to bout S on days 1, 2, 3, 5 and 6 (P < 0.05). Although serum creatine kinase activity was elevated after both exercise bouts (P < 0.01), there was no difference between bouts. Functional muscle damage markers and muscle soreness suggest greater damage after bout L. Post-exercise angle-specific force decrements suggest a transient increase in muscle length after bout L but not bout S.

Does Antioxidant Vitamin Supplementation Protect against Muscle Damage

The high forces undergone during repetitive eccentric, or lengthening, contractions place skeletal muscle under considerable stress, in particular if unaccustomed. Although muscle is highly adaptive, the responses to stress may not be optimally regulated by the body. Reactive oxygen species (ROS)are one component of the stress response that may contribute to muscle damage after eccentric exercise. Antioxidants may in turn scavenge ROS, thereby preventing or attenuating muscle damage. The antioxidant vitamins C (ascorbic acid) and E (tocopherol) are among the most commonly used sport supplements, and are often taken in large doses by athletes and other sportspersons because of their potential protective effect against muscle damage. This review assesses studies that have investigated the effects of these two antioxidants, alone or in combination, on muscle damage and oxidative stress. Studies have used a variety of supplementation strategies, with variations in dosage, timing and duration of supplementation. Although there is some evidence to show that both antioxidants can reduce indices of oxidative stress, there is little evidence to support a role for vitamin C and/or vitamin E in protecting against muscle damage. Indeed, antioxidant supplementation may actually interfere with the cellular signalling functions of ROS, thereby adversely affecting muscle performance. Furthermore, recent studies have cast doubt on the benign effects of long-term, high-dosage antioxidant supplementation. High doses of vitamin E, in particular, may increase all-cause mortality. Although some equivocation remains in the extant literature regarding the beneficial effects of antioxidant vitamin supplementation on muscle damage, there is little evidence to support such a role. Since the potential for long-term harm does exist, the casual use of high doses of antioxidants by athletes and others should perhaps be curtailed.

Stimulus artifact removal using a software-based two-stage peak detection algorithm

The analysis of stimulus evoked neuromuscular potentials or m-waves is a useful technique for improved feedback control in functional electrical stimulation systems. Usually, however, these signals are contaminated by stimulus artifact. A novel software technique, which uses a two-stage peak detection algorithm, has been developed to remove the unwanted artifact from the recorded signal. The advantage of the technique is that it can be used on all stimulation artifact-contaminated electroneurophysiologic data provided that the artifact and the biopotential are non-overlapping. The technique does not require any estimation of the stimulus artifact shape or duration. With the developed technique, it is not necessary to record a pure artifact signal for template estimation, a process that can increase the complexity of experimentation. The technique also does not require the recording of any external hardware synchronisation pulses. The method avoids the use of analogue or digital filtering techniques, which endeavour to remove certain high frequency components of the artifact signal, but invariably have difficulty, resulting in the removal of frequencies in the same spectrum as the m-wave. With the new technique the signal is sampled at a high frequency to ensure optimum fidelity. Instrumentation saturation effects due to the artifact can be avoided with careful electrode placement. The technique was fully tested with a wide variety of electrical stimulation parameters (frequency and pulse width) applied to the common peroneal nerve to elicit contraction in the tibialis anterior. The program was also developed to allow batch processing of multiple files, using closed loop feedback correction. The two-stage peak detection artifact removal algorithm is demonstrated as an efficient post-processing technique for acquiring artifact free m-waves.

Validation of MET estimates and step measurement using the ActivPAL physical activity logger

Abstract The purpose of this study was to determine the validity of the metabolic equivalent (MET) equation and step rate function of the ActivPAL™ physical activity logger in a group of females. Using a standard treadmill protocol, 62 females aged 15–25 years walked on a treadmill at speeds between 3.2 and 7.0 km · h−1 while wearing an ActivPAL. Oxygen consumption was measured using expired gas analysis at each speed and METs for each speed were estimated based on each participants own resting metabolic rate. A sub-set of 18 participants also wore an Actigraph. Results showed that the in-built equation in the ActivPAL significantly underestimated (P < 0.001) METs under treadmill conditions at higher intensities. The ActivPAL equation is based on step rate yet the relationship between counts and measured METs (r = 0.76; P < 0.001) is stronger than that between steps and measured METs (r = 0.59; P < 0.001). Both the ActivPAL and Actigraph step functions showed no significant difference (P > 0.05) to video recorded step rate except at the slowest walking speed where the Actigraph significantly underestimated steps (P < 0.05). The development of a new equation based on the counts–METs relationship that includes a variety of speeds and activities would be useful. The ActivPAL step function performs better than the Actigraph at the slowest walking speed under treadmill conditions.