Delayed Onset Muscle Soreness (DOMS) is a common response to activities involving lengthening contractions. Muscle inflammation is associated with DOMS and may play an integral role in protecting a muscle from damage and soreness in response to subsequent bouts of lengthening contractions. Research in animals has shown that prior exposure to passive stretching and isometric contractions of a muscle resulting in muscle inflammation attenuates the muscle inflammatory response following subsequent bouts of lengthening contractions. The purpose of this study was to determine whether passive stretching and isometric contractions in humans would reduce DOMS following a typical bout of resistance exercise. METHODS: Thirty untrained male subjects were assigned to a control (C), stretching (S) or isometric (I) contraction group (n=10/group). In the week prior to the typical resistance training bout subjects in S and I were exposed to 3 separate sessions involving 5 minutes of passive stretching or maximal isometric contractions, respectively. Passive and active soreness, thigh girth, and relaxed knee angle were assessed prior to intervention and on days 1, 2, 4, and 8 following the bout of resistance exercise. RESULTS: Passive and active muscle soreness increased similarly in all groups. However, active soreness returned higher values than passive soreness at several time points following resistance exercise. Peak soreness occurred at 48h post exercise. Thigh girth and relaxed knee angle reached their highest values at 5 minutes following resistance exercise however there were no differences between the groups. CONCLUSIONS: The present study demonstrates that a typical bout of resistance exercise is sufficient to cause measurable levels of DOMS in untrained subjects and that subjects are more sensitive to active measures of DOMS compared to a passive assessment. Nevertheless the passive stretching and isometric contraction interventions did nothing to reduce DOMS in the current subjects.

<p> The present study was undertaken to investigate the mechanism underlying the observation that the maximal voluntary strength of the two legs acting together or bilaterally in isometric leg extension was less than the summed unilateral (sum of the left and right legs tested separately) strength. Observations were made on this phenomenon under both isometric and concentric contraction conditions by testing young adult males performing unilateral and bilateral leg press contractions on a modified isokinetic dynamometer. </p> <p> Electromyographical evidence indicated that there was a lesser activation of motor units in bilateral contraction as compared to unilateral, under isometric conditions and at a low and high concentric velocity. To determine whether a particular type of motor unit was being activated to a lesser extent in bilateral contractions, two physiological parameters of unilateral and bilateral contractions were compared: the strength-velocity relation and fatigability. This investigative method was based on the known physiological differences between the motor unit types; namely fast-twitch (FT), type two motor units have a faster twitch contraction time, greater force output at high velocities of shortening and lesser resistance to fatigue than the slow-twitch (ST), type one units. </p> <p> Results showed a greater relative decline in the strength of bilateral contractions as the velocity of contraction was increased through a range from 0°/s to 424°/s (0 to 7.40 radians/s). The bilateral to summed unilateral strength ratio (B/U-ratio) decreased from 0.91 under isometric conditions to 0.51 at the highest test velocity. Lesser fatigability was found in the bilateral condition in a 100 consecutive concentric contraction fatigue test. These results provided complementary evidence for the conclusion that FT motor units were active to a lesser degree in bilateral contractions. </p> / Thesis / Master of Science (MSc)

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Purpose: The purpose of this study was to investigate the origins of differing tonic muscle activity in three populations with known differences in neuromuscular processing. Methods: We manipulated healthy young adults, healthy older adults and individuals with Parkinson's disease (PD), both on and off dopamine therapy medication, with a novel technique related to muscle after contraction (MAC). We also investigated the transfer of tonic activity to the contralateral (unmanipulated) limbs to determine whether tonic activity is modulated through inhibitory and facilitatory interneuronal processes at a peripheral, spinal, or supraspinal level. In independent trials, we examined MAC in both proximal (medial deltoid) and distal (tibialis anterior) postural musculature by having subjects perform a voluntary, isometric contraction of the upper arm or ankle, respectively. Using surface electromyography (sEMG) to record the activity of the motor units before, during and after contraction, we were able to examine the differences in motor unit recruitment across the different populations from both an amplitude and frequency analyses. To test the transfer of tonic muscle activity to contralateral limbs, we manipulated conscious attention by having individuals focus on the unmanipulated limb during the post-contraction phase. Results: Our result shows significant changes in the prevalence of MAC with age and disease state. Moreover, some subjects with PDs showed variable evidence of tonic motor irradiation across the body, which was not seen in healthy individuals. Subjects with PD also showed unintended involuntary movement in the contralateral limb when treating the affected side, but were able to inhibit this behavior when explicit attention was paid to the unmanipulated side. Healthy young adult subjects consistently showed a MAC in their medial deltoids. Healthy older adults returned to baseline muscle activity following a contraction. During the attention conditions, there was increased muscle activity in the contralateral limb across subject groups. Conclusions: The findings from this series of studies may deepen our understanding of how aging and neural disease affect the unconscious tonic neuromuscular processes that serve as the foundation for all motor activity. This may help shape future rehabilitation techniques, particularly in decreasing fall risk, for the PD population as well as healthy agers. / Bioengineering

<p> A novel method has been developed to determine the quantitative relationship between the percentage ofla fibres stimulated synchronously, and the percentage of human flexor carpi radialis (FCR) motoneurons (MNs) discharged reflexly. The method assumes a normal distribution of Ia fibre thresholds to electrical stimulation. Among the 11 healthy subjects tested during relaxation, there were considerable differences in the reflex excitability of the FCR MNs to quantitative Ia fibre inputs. The Ia fibre input-FCR MN output curves were either initially steeply-rising, initially slowly-rising, or initially and latterly steeply-rising. When the results were averaged, however, the curve for the 11 subjects in the relaxed state appeared to be fairly linear throughout the entire range of the Ia fibre inputs, and a mean of82% of the Ia fibres discharged approximately 20% of theMNs. </p> <p> Regardless of the variability in the shape of individual input-output curves during relaxation, potentiation of the FCR MN output was observed during weak wrist flexion in 10 of the 11 subjects over the full range of the Ia fibre inputs. In contrast, a depression of the MN output was exhibited in all 8 subjects who weakly contracted the extensors over the full range of the Ia fibre inputs. The changes in the Ia input-MN output relationship in going from rest to voluntary contractions of wrist muscles are thought to reflect modulation by presynpatic inhibition of the Ia terminals. With very large Ia inputs during wrist extension, however, there is a steep rise in the input-output curve, which could indicate a decrease in presynaptic inhibition of Ia terminals in the FCR muscle. The modulation ofthe input-output relationship observed in the present study is consistent with the task-dependent differences of reflex excitability observed by Stein et al. (1988). </p> / Thesis / Master of Applied Science (MASc)