Lara A. Green

Quantifying the familiarization period for maximal resistive exercise

Resistive exercise is used in the assessment of musculoskeletal health, performance, training interventions, and population differences (i.e., gender, age, training status). There is a need to determine the amount of familiarization required to stabilize performance prior to testing. Fifteen males completed a familiarization session consisting of 3 blocks of 5 maximal isometric dorsiflexion contractions, followed by a retention test (an additional block of 5 contractions) performed 3 days later. Mean force and surface electromyography (sEMG) from both the agonist and antagonist muscles were collected. A variance ratio, representing the stability between trials, was calculated for each of the 4 blocks of 5 contractions for both force and sEMG. The variance ratio for both force and agonist sEMG decreased significantly within the first 10 trials and remained stable during the retention test. The variance ratio for antagonist sEMG was stable across the 3 blocks of familiarization and significantly decreased during the retention test. The magnitude variables all remained stable across the 3 familiarization blocks. However, an 11% increase in mean force was seen during the retention test while both agonist and antagonist sEMG remained stable. Although slight changes occurred in the magnitude variables during the retention test, the stabilization of the force and agonist sEMG variance ratios suggest that familiarization to the task was achieved within the first 10 contractions and was sustained over a 3-day period.

Flexor carpi radialis surface electromyography electrode placement for evoked and voluntary measures.

Introduction: In this study we evaluated the reliability of bipolar electrode recordings, which allow for undistorted compound muscle action potentials (CMAPs) while minimizing cross‐talk during voluntary contractions. Methods: Twenty‐four men completed maximal voluntary wrist flexion contractions in 4 test sessions. Compound muscle action potentials were also evoked during each session. Surface electromyography was recorded from the flexor carpi radialis (FCR) with the recording electrode (G1) placed on the motor point and a second recording electrode (G2) adjacent to G1. Reliability was assessed using intraclass correlational analysis of variance and standard error of measurement. Results: Root‐mean‐square (RMS) amplitude and mean power frequency (MPF) were highly reliable (R = 0.89 and 0.84, respectively). The CMAPs also exhibited good reliability (R = 0.75). Normalization of RMS amplitude reduced the intraclass reliability coefficient (R = 0.85). Conclusion: The electrode placement resulted in reliable measures from voluntary contractions and CMAPs. Normalization can decrease reliability. Muscle Nerve 52: 818–825, 2015

Task complexity and maximal isometric strength gains through motor learning

This study compared the effects of a simple versus complex contraction pattern on the acquisition, retention, and transfer of maximal isometric strength gains and reductions in force variability. A control group (N = 12) performed simple isometric contractions of the wrist flexors. An experimental group (N = 12) performed complex proprioceptive neuromuscular facilitation (PNF) contractions consisting of maximal isometric wrist extension immediately reversing force direction to wrist flexion within a single trial. Ten contractions were completed on three consecutive days with a retention and transfer test 2‐weeks later. For the retention test, the groups performed their assigned contraction pattern followed by a transfer test that consisted of the other contraction pattern for a cross‐over design. Both groups exhibited comparable increases in strength (20.2%, P < 0.01) and reductions in mean torque variability (26.2%, P < 0.01), which were retained and transferred. There was a decrease in the coactivation ratio (antagonist/agonist muscle activity) for both groups, which was retained and transferred (35.2%, P < 0.01). The experimental group exhibited a linear decrease in variability of the torque‐ and sEMG‐time curves, indicating transfer to the simple contraction pattern (P < 0.01). The control group underwent a decrease in variability of the torque‐ and sEMG‐time curves from the first day of training to retention, but participants returned to baseline levels during the transfer condition (P < 0.01). However, the difference between torque RMS error versus the variability in torque‐ and sEMG‐time curves suggests the demands of the complex task were transferred, but could not be achieved in a reproducible way.

Elevated concentrations of circulating cytokines and correlations with nerve conduction velocity in human peripheral nerves

The purpose of the current study was to quantify the potential relationship between various cytokines and peripheral nerve function in humans, in-vivo. Measures of nerve conduction velocity (NCV) were examined prior to and following the induction of a cytokine spike. A significant negative correlation was found between the change in IL-1ra and the change in NCV at 24h post-exercise (r=-0.65, p=0.02) while a significant positive correlation was found between the change in IL-6 and the change in NCV at 2h post-exercise (r=0.61, p=0.048). It may be possible that different cytokines induce a unique neural influence at elevated concentrations.

The cross education of strength and skill following unilateral strength training in the upper and lower limbs

Cross education is the strength gain or skill improvement transferred to the contralateral limb following unilateral training or practice. The present study examined the transfer of both strength and skill following a strength training program. Forty participants (20M, 20F) completed a 6-wk unilateral training program of dominant wrist flexion or dorsiflexion. Strength, force variability, and muscle activity were assessed pretraining, posttraining, and following 6 wk of detraining (retention). Analyses of covariance compared the experimental limb (trained or untrained) to the control (dominant or nondominant). There were no sex differences in the training response. Cross education of strength at posttraining was 6% ( P < 0.01) in the untrained arm and 13% ( P < 0.01) in the untrained leg. Contralateral strength continued to increase following detraining to 15% in the arm ( P < 0.01) and 14% in the leg ( P < 0.01). There was no difference in strength gains between upper and lower limbs ( P > 0.05). Cross education of skill (force variability) demonstrated greater improvements in the untrained limbs compared with the control limbs during contractions performed without concurrent feedback. Significant increases in V-wave amplitude ( P = 0.02) and central activation ( P < 0.01) were highly correlated with contralateral strength gains. There was no change in agonist amplitude or motor unit firing rates in the untrained limbs ( P > 0.05). The neuromuscular mechanisms mirrored the force increases at posttraining and retention supporting central drive adaptations of cross education. The continued strength increases at retention identified the presence of motor learning in cross education, as confirmed by force variability. NEW & NOTEWORTHY We examined cross education of strength and skill following 6 wk of unilateral training and 6 wk of detraining. A novel finding was the continued increase in contralateral strength following both training and detraining. Neuromuscular adaptations were highly correlated with strength gains in the trained and contralateral limbs. Motor learning was evident in the trained and contralateral limbs during contractions performed without concurrent feedback.