Comparative Acceptability of Weightbearing Physical Activity in Sporting Footwear Versus Barefoot in Habitually Shod Individuals.

BACKGROUND: Perceived acceptability of barefoot use has largely been ignored in the literature despite its importance to long-term implementation and behavior change. This study aimed to compare the acceptability of undertaking weightbearing physical activities in regular running shoes versus barefoot in habitually shod individuals. METHODS: Healthy young men and women were recruited from the Gold Coast. Participants completed six activities (ie, lunges, walking, jogging, sidestep, vertical jump, and hop) in shod and barefoot conditions then answered questions pertaining to level and source of discomfort, ease of performance, and acceptability. Indices of bone quality were measured from their dominant calcaneus by quantitative ultrasound. RESULTS: Seventeen healthy male (n = 8) and female (n = 9) university students participated in the study (age, 26.59 ± 7.26 years; body mass index, 23.08 ± 3.58 kg/m2). Men were taller, heavier, and had higher broadband ultrasound attenuation than women (P < .05). For "no" discomfort, "very easy" ease of performance, and a "good amount" or "very good amount" of acceptability, the shod condition demonstrated response rates of 87.25%, 55.88%, and 72.55%, respectively. The barefoot condition demonstrated rates of those responses of 62.75%, 39.22%, and 48.03%, respectively, and reported more ball-of-foot, forefoot, heel, and plantar skin locations as sources of discomfort during activity than in the shod condition. The group vertical jump height was higher barefoot than shod (44.88 ± 8.44 cm and 43.25 ± 8.76 cm, respectively; P < .05), but no difference was seen for the hop. Men jumped and hopped higher than women under both footwear conditions (P < .05). CONCLUSIONS: Participants initiating barefoot weightbearing exercise may experience slightly greater discomfort and less ease of performance in the initial transition from the shod condition, but may perform better in vertical jump. Whether those differences in experience persist over the long term will require longitudinal studies.

Test-retest reliability of laser displacement mechanomyography in paraspinal muscles while in lumbar extension or flexion.

This study investigated test-retest reliability of mechanomyography (MMG) on lumbar paraspinal muscles. Healthy male and female subjects (mean ±â€¯standard deviation, 25 ±â€¯9.4 years, BMI 21.8 ±â€¯2.99, n = 34) were recruited. Two test sessions (one week apart) consisted of MMG (laser displacement sensor (LDS)) muscle evaluations over the 10 lumbar facet joints, and 2 bilateral sacral sites, in anatomical extension and flexion. Two-way repeated measures ANOVA with Tukey's post hoc showed no significant differences between testing sessions for the same position (p > 0.05). The intra-class correlation coefficients (ICCs) in extension were classified as 'very good' (0.8-0.9) for maximal muscle displacement (Dmax), contraction time (Tc) and velocity of contraction (Vr). Half relaxation time (½Tr) and half relaxation velocity (½Vr) were 'poor' (0.4-0.5) and 'good' (0.7-0.8). In flexion, Dmax, Tc and Vr were 'excellent' (≥0.9) whilst ½Tr and ½Vr were 'fair' (0.6-0.7) and 'very good'. Comparing extension against flexion, significant (p < 0.05) differences in Dmax and ½Vr were found (L1/L2-L5/S1). Tc was significant (p < 0.05) for all sites whilst Vc was for L1/L2 on both sides (p < 0.05). ½Tr showed no significance (p > 0.05). Most MMG-derived parameters thus appear as reliable measures of muscle contractile properties in lumbar extension and flexion, with flexion providing more reliable results (ICCs).

Test-Retest Reliability and Reproducibility of Laser- versus Contact-Displacement Sensors in Mechanomyography: Implications for Musculoskeletal Research.

Whole muscle mechanomyography (MMG) has gained considerable interest in recent years for its ability to noninvasively determine muscle contractile properties (ie, contraction time [Tc], half-relaxation time [1/2Tr], and maximal displacement [Dmax)]). The aim of this study was to evaluate the test-retest reliability of two fairly novel MMG transducers: a laser-displacement sensor (LDS) and contact-displacement sensor (CDS). MMG was conducted on the rectus femoris muscle of 30 healthy individuals on 4 separate occasions. Test-retest reliability was quantified using intraclass correlation coefficients (ICCs). Both sensors were reliable for time-derived parameters Tc (ICCs, 0.85-0.88) and 1/2Tr (0.77-0.89), with Dmax identified as the most reproducible parameter (0.89-0.94). The 2 sensors produced similar Tc and Dmax measures, although significant (P < .05) systematic bias was identified with the CDS recording higher mean values, on average. However, these differences may not be considered clinically significant. The wide limits of agreement identified between 1/2Tr measures (-19.0 ms and 25.2 ms) are considered unreliable from a clinical perspective. Overall, MMG demonstrated good-to-excellent reliability for the assessment of muscle contractile properties with no significant differences identified between sessions, thus further validating its applicability as a noninvasive measure of muscle contractile properties.

The effect of exercise hypertrophy and disuse atrophy on muscle contractile properties: a mechanomyographic analysis.

PURPOSE: To determine whether mechanomyographic (MMG) determined contractile properties of the biceps brachii change during exercise-induced hypertrophy and subsequent disuse atrophy. METHODS: Healthy subjects (mean ± SD, 23.7 ± 2.6 years, BMI 21.8 ± 2.4, n = 19) performed unilateral biceps curls (9 sets × 12 repetitions, 5 sessions per week) for 8 weeks (hypertrophic phase) before ceasing exercise (atrophic phase) for the following 8 weeks (non-dominant limb; treatment, dominant limb; control). MMG measures of muscle contractile properties (contraction time; T c, maximum displacement; D max, contraction velocity; V c), electromyographic (EMG) measures of muscle fatigue (median power frequency; MPF), strength measures (maximum voluntary contraction; MVC) and measures of muscle thickness (ultrasound) were obtained. RESULTS: Two-way repeated measures ANOVA showed significant differences (P < 0.05) between treatment and control limbs. During the hypertrophic phase treatment MVC initially declined (weeks 1-3), due to fatigue (decline in MPF), followed by improvement against control during weeks 6-8. Between weeks 5 and 8 treatment, muscle thickness was greater than control, reflecting gross hypertrophy. MMG variables Dmax (weeks 2, 7) and Vc (weeks 7, 8) declined. During the atrophic phase, MVC (weeks 9-12) and muscle thickness (weeks 9, 10) initially remained high before declining to control levels, reflecting gross atrophy. MMG variables D max (weeks 9, 14) and V c (weeks 9, 14, 15) also declined during the atrophic phase. No change in T c was found throughout the hypertrophic or atrophic phases. CONCLUSIONS: MMG detects changes in contractile properties during stages of exercise-induced hypertrophy and disuse atrophy suggesting its applicability as a clinical tool in musculoskeletal rehabilitation.

Determining minimal stimulus intensity for mechanomyographic analysis.

INTRODUCTION: Mechanomyography (MMG) has recently shown promise in monitoring recovery of injured muscles. However, delivering a maximal percutaneous neuromuscular stimulus (PNS) could potentially be painful on severely damaged muscles. The aim of this paper was to determine whether delivering a sub-maximal PNS could still obtain accurate MMG recordings of muscle contraction time (Tc). The effect of muscle architecture on determining the minimal level of current was also investigated. METHODS: Six muscles were investigated; 5 lower limb and the 1st dorsal interosseous. A 'current ramp' procedure was performed to determine minimal stimulus intensity required for accurate Tc recordings. A current ramp entails beginning at a low current (30mA) and increasing in increments of 10mA until a maximal muscle contraction is observed. RESULTS: For lower limb muscles, 130mA was the largest current required to obtain accurate Tc recordings in at least 95% of the population. This was up to a 50% reduction in the amount of current delivered for some muscles. Fibre type distribution showed the greatest relationship with mean minimum current. DISCUSSION: Future studies investigating injured or uninjured muscles via MMG, could use these submaximal currents to obtain accurate MMG recordings, whilst improving patient comfort and reducing experiment duration.