Head-down tilt bed rest with or without artificial gravity is not associated with motor unit remodeling

© 2020, The Author(s). Purpose: The objective of this study was to assess whether artificial gravity attenuates any long-duration head-down 60 bed rest (HDBR)-induced alterations in motor unit (MU) properties. Methods: Twenty-four healthy participants (16 men; 8 women; 26–54 years) underwent 60-day HDBR with (n = 16) or without (n = 8) 30 min artificial gravity daily induced by whole-body centrifugation. Compound muscle action potential (CMAP), MU number (MUNIX) and MU size (MUSIX) were estimated using the method of Motor Unit Number Index in the Abductor digiti minimi and tibialis anterior muscles 5 days before (BDC-5), and during day 4 (HDT4) and 59 (HDT59) of HDBR. Results: The CMAP, MUNIX, and MUSIX at baseline did not change significantly in either muscle, irrespective of the intervention (p > 0.05). Across groups, there were no significant differences in any variable during HDBR, compared to BDC-5. Conclusion: Sixty days of HDBR with or without artificial gravity does not induce alterations in motor unit number and size in the ADM or TA muscles in healthy individuals

Vibration or balance training on neuromuscular performance in osteopenic women

Maintaining neuromuscular function in older age is an important topic for aging societies, especially for older women with low bone density who may be at risk of falls and bone fracture. This randomized controlled trial investigated the effect of resistive exercise with either whole-body vibration training (VIB) or coordination/balance training (BAL) on neuromuscular function (countermovement jump, multiple 1-leg hopping, sit-to-stand test). 68 postmenopausal women with osteopenia or osteoporosis were recruited for the study. 57 subjects completed the 9-month, twice weekly, intervention period. All subjects conducted 30 min of resistance exercise each training day. The VIB-group performed additional training on the Galileo vibration exercise device. The BAL-group performed balance training. An "intent-to-treat" analysis showed greater improvement in the VIB-group for peak countermovement power (p=0.004). The mean [95% confidence interval] effect size for this parameter was a  + 0.9[0.3 to 1.5] W/kg greater change in VIB than BAL after 9 months. In multiple 1-leg hopping, a significantly better performance in the VIB-group after the intervention period was seen on a "per-protocol" analysis only. Both groups improved in the sit-to-stand test. The current study provides evidence that short-duration whole-body vibration exercise can have a greater impact on some aspects of neuromuscular function in post-menopausal women with low bone density than proprioceptive training

Quantification of the timing of continuous modulated muscle activity in a repetitive-movement task

The timing of muscle activity is commonly measured in studies of motor control. In repetitive- movement tasks, muscle activity may be continuous, and no defined onset or offset of activity may be measured. This does not imply that no timing of muscle activity occurs. Where activity is continuous, this timing will typically be exhibited by modulation of the amplitude of the signal in specific movement phases. The existence of this electromyographic (EMG) timing is dependent upon the existence of EMG amplitude modulation. This paper investigates this relationship in developing a quantification algorithm of EMG timing in a repetitive-movement task. A frequency domain quantification algorithm involving EMG linear-envelope generation is used. An EMG simulation algorithm is used to test this algorithm and determine the minimal amplitude-modulation threshold for timing detection. At five repetitive-movement speeds (25, 50, 75, 100 and 125 cycles of movement per minute), thresholds between 1.558 and 2.326 times maximal to minimal linear-envelope amplitude are required for reliability of timing detection. Analysis of variance indicates that the robustness of the quantification algorithm was not significantly affected by burst width (F = 3.69, p = 0.055) or the underling input timing parameter (F = 0.52, p = 0.992). The phase-lead/lag quantification algorithm represents a useful tool for the analysis motor control via EMG during repetitive- movement tasks

Physical activity accumulation along the intensity spectrum differs between children and adults

Purpose Detailed exploration of physical activity accumulation with fine grading along the intensity spectrum has indicated the potential pragmatic utility of such an approach. However, it is currently unclear what sorts of accumulation patterns along particular intensity bands are found in the children and adult populations. Therefore, we conducted a comparison of activity accumulation in specific intensity bands between four distinct populations: children, adults with sedentary lifestyles, habitual joggers, habitual marathon runners. Methods Free-living waist-worn accelerometry records from 28 children aged 7 to 11, and 61 adults aged 25 to 35 were analysed. Activity intensity was evaluated in 5 s non-overlapping epochs as mean amplitude deviation (MAD) and normalised to acceleration intensities corresponding to walking at 3 metabolic equivalents of a task (METs). Adult data were normalised to 0.091 g MAD based on literature, and data from children to 0.170 g MAD based on laboratory experimentation. The normalised epoch values were divided into 100 intensity gradations. Results Children accumulated more activity in 0.74 to 1.58 normalised acceleration intensities (all p < 0.005) compared to adults. Adult joggers/runners accumulated more activity in normalised acceleration intensities from 7.1 to 11.1 compared to the other groups (p < 0.008). Conclusion The primary bulk of children’s free-living activities are of relatively low intensity not likely to provoke cardiometabolic improvement. These sorts of explorations could be used in informing intervention development aiming at optimising healthy development. Evidence is mounting to justify randomised controlled trials based on intervention targets identified based on exploring the intensity spectrum.peerReviewe

Bone density and neuromuscular function in older competitive athletes depend on running distance

Summary Individuals who are involved in explosive sport types, such as 100-m sprints and long jump, have greater bone density, leg muscle size, jumping height and grip strength than individuals involved in long-distance running. Introduction The purpose of this study is to examine the relationship between different types of physical activity with bone, lean mass and neuromuscular performance in older individuals. Methods We examined short- (n050), middle- (n019) and long-distance (n0109) athletes at the 15th European Masters Championships in Poznań, Poland. Dual X-ray absorptiometry was used to measure areal bone mineral density (aBMD) and lean tissue mass. Maximal countermovement jump, multiple one-leg hopping and maximal grip force tests were performed. Results Short-distance athletes showed significantly higher aBMD at the legs, hip, lumbar spine and trunk compared to long-distance athletes (p≤0.0012). Countermovement jump performance, hop force, grip force, leg lean mass and arm lean mass were greater in short-distance athletes (p≤0.027). A similar pattern was seen in middle-distance athletes who typically showed higher aBMD and better neuromuscular performance than long-distance athletes, but lower in magnitude than short-distance athletes. In all athletes, aBMD was the same or higher than the expected age-adjusted population mean at the lumbar spine, hip and whole body. This effect was greater in the short- and middle-distance athletes. Conclusions The stepwise relation between short-,middle- and long-distance athletes on bone suggests that the higher-impact loading protocols in short-distance disciplines are more effective in promoting aBMD. The regional effect on bone, with the differences between the groups being most marked at loadbearing regions (legs, hip, spine and trunk) rather than nonload- bearing regions, is further evidence in support of the idea that bone adaptation to exercise is dependent upon the local loading environment, rather than as part of a systemic effect