Recent evidence indicates that regular physical activity enhances brain plasticity (i.e. the ability to reorganise neural connections) and improves neurocognitive function. However, the effect of regular physical activity on human motor cortex function is unknown. The purpose of this study was to examine motor cortex plasticity for a small hand muscle in highly active and sedentary individuals. Electromyographic recordings were obtained from the left abductor pollicis brevis (APB) muscle of 14 active and 14 sedentary subjects (aged 18-38 yrs). The extent of physical activity was assessed by questionnaire, where the physically active subjects performed >150 min per day moderate-to-vigorous aerobic activity on at least 5 days per week, whereas the sedentary group performed <20 min per day of physical activity on no more than 3 days per week. Transcranial magnetic stimulation (TMS) of the right hemisphere was used to assess changes in APB motor-evoked potentials (MEPs), input-output curve (IO curve), short-interval intracortical inhibition (SICI) and cortical silent period (CSP). Neuroplastic changes were induced using paired-associative stimulation (PAS), which consisted of 90 paired stimuli (0.05 Hz for 30 min) of median nerve electrical stimulation at the wrist followed 25 ms later by TMS to the hand area of motor cortex. The IO curve slope was 35% steeper in individuals with increased physical activity (combined before and after PAS, P < 0.05), suggesting increased motor cortex excitability, although there was no difference in SICI or CSP between groups. PAS induced an increase in MEP amplitude in the physically active subjects (54% increase compared with before, P < 0.01), but no significant facilitation in the sedentary subjects. We conclude that participation in regular physical activity may offer global benefits to motor cortex function that enhances neuroplasticity, which could improve motor learning and neurorehabilitation in physically active individuals.

This study tested the hypothesis that eccentric exercise (ECC) would increase force fluctuation for several days following exercise; however, concentric exercise (CON) would not produce such an effect. Twelve men performed six sets of five reps of dumbbell exercise of the elbow flexors eccentrically with one arm and concentrically with the other, separated by 4-6 weeks, using a dumbbell set at 50% of maximal voluntary isometric contraction (MVC) measured at 90 degrees of elbow flexion. MVC, range of motion (ROM), upper arm circumference, plasma creatine kinase activity (CK), myoglobin concentration (Mb) and muscle soreness were assessed before, immediately after, 1 h and 1-5 days following both exercise bouts. Force fluctuations during 30, 50 and 80% MVC were quantified by coefficient of variation (CV) of the force data (sampling frequency: 100 Hz) for 4 s. Significantly (P < 0.01) larger changes in MVC, ROM, and upper arm circumference were evident following ECC compared to CON, and only ECC resulted in significant (P < 0.01) increases in CK and Mb, and development of muscle soreness. Significant (P < 0.01) differences existed between ECC and CON for changes in force fluctuations. CV increased significantly (P < 0.01) immediately and 1 h after ECC from baseline for 30, 50, and 80% MVC without a significant difference among the intensities, and no significant changes in CV were evident following CON. It was concluded that increases in force fluctuation were peculiar to ECC, but did not necessarily reflect muscle damage.

This study aimed to investigate if old men were more susceptible than young men to muscle damage induced by exercise consisting of repeated-lengthening muscle actions. The responses to a bout of eccentric exercise were compared between 10 young (mean age +/- SEM = 19.4 +/- 0.4 y) and 10 old (70.5 +/- 1.5 y) men. All subjects performed 6 sets of 5 lengthening actions of the left elbow flexors at a range of 90 degrees from an elbow flexed (90 degrees ) to an extended (180 degrees ) position in 5 s using a dumbbell massed at 40% maximal isometric strength (MVC) at an elbow joint angle of 90 degrees . Changes in MVC, range of motion (ROM), upper arm circumference (CIR), muscle soreness (DOMS), plasma creatine kinase activity (CK), and myoglobin (Mb) concentration over 7-10 d following exercise were compared between groups by 2-way repeated measures analysis of variance (ANOVA). Significant differences between groups were evident at baseline for ROM (significantly smaller for the older group) and CIR (significantly larger for the older group), but not for MVC and other measures. Contrary to the hypothesis, the young group showed significantly larger decreases in MVC and ROM and larger increases in circumference, DOMS, CK activity, and Mb con centration than those of the old group. These results suggest that muscle damage is not necessarily greater in old versus young men following voluntary eccentric exercise. It may be that physiological changes that occur with ageing, including a decrease in ROM, reduce damaging stress to muscles during lengthening muscle actions.

Contrary to the hypothesis, S-ECC provided partial but effective protection against L-ECC. This result suggests adaptations associated with the repeated bout effect were also produced after S-ECC, but the degree of adaptations was not as strong as that by L-ECC. Eccentric exercise at a short extension range can be used as a strategy to present severe muscle damage.

Summary This study investigated the hypothesis that a light eccentric exercise (ECC) that does not induce a loss of muscle function and delayed onset muscle soreness would confer a protective effect against a more strenuous ECC. Eighteen young men were randomly placed into two groups: 10-40% (n = 9) and 40% (n = 9). Subjects in the 10-40% group performed ECC of the elbow flexors (six sets of five reps) using a dumbbell set at 10% of maximal isometric strength (MVC) at an elbow joint angle of 90 • , followed 2 days later by ECC using a dumbbell weight of 40% MVC. Subjects in the 40% group performed the 40% ECC only. Changes in MVC, range of motion (ROM), upper arm circumference (CIR), plasma creatine kinase (CK) activity and muscle soreness before, immediately after, 1-5 and 7 days following the 40% ECC were compared between groups by a two-way repeated measures ANOVA. No significant changes in any of the criterion measures were found immediately and 1-2 days after the 10% ECC. Following the 40% ECC, the 10-40% group showed significantly (P < 0.05) smaller decreases in MVC and ROM, and smaller increases in muscle soreness compared with the 40% group, but no significant differences between groups were evident for CIR and plasma CK activity. These results suggest that the 10% ECC induced some protection against a subsequent bout of 40% ECC performed 2 days later. It appears that the light eccentric exercise preconditioned the muscles for exposure to the subsequent damaging eccentric exercise bout.