Objective: To determine the relationship between muscle density and neuromusculoskeletal status in stroke survivors with subacute and chronic hemiparesis. Methods: Community-dwelling adults were recruited into one of 3 groups (11 per group): subacute stroke group (SSG, <6 months post-stroke), chronic stroke group (CSG, >1 year post-stroke), or age- and gender-matched control group (CG). Muscle density, muscle mass and tibial bone status (cortical density, mass and polar stress-strain index (pSSI)) were measured bilaterally at the tibial 66% site using peripheral quantitative computed tomography. Muscle strength of ankle plantarflexors and knee extensors was assessed using isokinetic dynamometry. Mobility was assessed using the Berg Balance Scale. Univariate regression analyses by group tested whether side-to-side differences in muscle density and measures of neuromusculoskeletal status were related. Results: In the SSG and CG, relationships were observed for muscle density and ankle plantarflexor strength (R² = 0.365 and 0.503). Muscle density related to muscle mass in the CG only (R² = 0.889). Muscle density related to cortical bone density in the SSG (R² = 0.602) and pSSI in the CSG (R² = 0.434). Conclusions: Muscle density may provide insight into the side-to-side changes in muscle and bone strength following hemiparetic stroke.

Objectives: To describe mechanographic tests that can be performed by patients with a range of functional abilities and to assess the reproducibility of test results in healthy adults and children. Methods: Fifteen adults and 13 children underwent two separate sessions, one week apart. Participants performed five different tests in both sessions: Multiple one-legged hopping, multiple two-legged hopping, single two-legged jump, heel-rise test, chair-rise test. All measurements were recorded with a portable force platform. Results: The main outcome measures of each test (peak force relative to body weight or peak power relative to body weight, depending on the test) showed no systematic differences between Session 1 and 2 for any of the test results. Coefficients of variation for the suggested main outcome parameters ranged between 3.4% and 7.5% for multiple one-legged hopping, multiple two-legged hopping, single two-legged jump and the heel-rise test, but were higher for the chair-rise test (8.0% in adults, 15.6% in children). Conclusions: The five mechanographic tests assessed in the present study yield reproducible outcome measures in healthy subjects. It is justified to evaluate the usefulness of these tests in different patient populations.

Oxidation alters calcium sensitivity, and decreases maximum isometric force (P_o) and shortening velocity (V_max) of single muscle fibres. To examine the effect of oxidation on the curvature of the force-velocity relationship, which determines muscle power in addition to P_o and V_max, skinned rat type I fibres were maximally activated at 15°C in a solution with pCa 4.5 and subjected to isotonic contractions before and after 4-min incubation in 50 mM H₂O₂ (n=10) or normal relaxing solution (n=3). In five oxidised and four control fibres the rate of force redevelopment (k_tr), following a rapid release and re-stretch, was measured. This gives a measure of the sum of the rate constants for cross-bridge attachment (f) and detachment (g₂): (f+g₂). H₂O₂ reduced P_o, V_max and k_tr by 19%, 21% and 24% respectively (P<0.001), while the shape of the force-velocity relationship was unchanged. Fitting data to the Huxley cross-bridge model suggested that oxidation decreased both the rate constant for cross-bridge attachment (f), and detachment of negatively strained cross-bridges (g₂), similar to the effect of reduced activation¹. This suggests that oxidative modification is a possible cause of the variation in contractile properties between muscle fibres of the same type².

Objective: Dynamic loads lead to increases in bone mass. How long these gains are maintained after cessation of loading, however, is not fully understood. Methods: A long-term study was performed in which skeletal changes were monitored by pQCT every 2-4 weeks (wks) for a 12 wk period after application of external loading using four-point bending device on 10 wk old female C57BL/6J mice. Results: 2 wks of loading caused 15-40% increase in bone parameters (vBMD, cross-sectional area (CSA)) and bone strength (yield load, maximum load and toughness). Positive correlations between these two parameters (r= 0.72 to 0.88, p<0.05) suggest that the changes in bone parameters induced by loading are responsible, in part, for the increase in bone strength. Once loading is terminated the bone response did not continue. The vBMD gained by loading was significant for a period of 5 wks and returned to the levels of controls at 12 wks. The CSA though declined but was still significantly elevated at 12 wks. Bone strength showed no difference between loaded and non-loaded bones at 12 wks. Conclusion: Our results show that external loading increased bone mass, was maintained for several weeks after termination of last loading.

Objectives: Various forms of adrenocortical insufficiency can cause musculoskeletal symptoms such as muscle pain, tautness of the limbs, arthralgia, and flexion contractures. However, the findings of neurological investigations are inconclusive and have not been well summarized. Methods: We report the case of a 61-year-old man with isolated adrenocorticotropic hormone deficiency who presented with musculoskeletal symptoms, including flexion contractures. We performed three neurological investigations: nerve conduction studies, electromyography, and muscle biopsy analysis. Further, we reviewed reports of 16 patients with various forms of adrenocortical insufficiency and musculoskeletal symptoms by considering the findings of these three investigations. Results: From the literature review, we found that (a) analysis of muscle biopsy is the most sensitive technique, followed by electromyography and then nerve conduction studies; and (b) the longer the duration of the musculoskeletal symptoms, the greater the incidence of abnormal findings with all three techniques. Conclusions: Physicians may prioritize neurological investigations, depending on these findings.