Ankle stiffness in postmenopausal women: influence of hormone therapy and menopause nature

Free-oscillation technique: The effect of the magnitude of the impulse applied on muscle and tendon stiffness around the ankle

The importance of the muscle-tendon complex in sport and for activities of everyday living is well recognised. The free oscillation technique is frequently used to determine the musculo-articular "apparent" stiffness (obtained from vertical ground reaction force) and other parameters. However, an in-depth understanding of the muscle-tendon complex can be gained by separating the muscle (soleus) and the tendon (Achilles tendon) components and studying the "true" stiffness for each of these components (by considering the ankle joint moment arms), which can be valuable in improving our understanding of training, injury prevention, and recovery programs. Hence, this study aimed to investigate if muscle and tendon stiffness (i.e., "true" stiffness) are similarly affected by different impulse magnitudes when using the free-oscillation technique. Three impulse magnitudes (impulse 1, 2 and 3), corresponding to peak forces of 100, 150 and 200 N, were used to estimate the stiffness of the ankle joint in 27 males, using multiple loads (10, 15, 20, 25, 30, 35, and 40 kg). A significant decrease (p < 0.0005) was found in musculo-articular "apparent" stiffness (29224 ± 5087 N.m-1; 27839 ± 4914 N.m-1; 26835 ± 4880 N.m-1) between impulses 1, 2 and 3 respectively, when loads were collapsed across groups. However, significant differences (p < 0.001) were only found between the median (Mdn) of impulse 1 (Mdn = 564.31 (kN/m)/kN) and 2 (Mdn = 468.88 (kN/m)/kN) and between impulse 1 (Mdn = 564.31 (kN/m)/kN) and 3 (Mdn = 422.19 (kN/m)/kN), for "true" muscle stiffness, but not for "true" tendon stiffness (Mdn = 197.35 kN/m; Mdn = 210.26 kN/m; Mdn = 201.60 kN/m). The results suggest that the musculo-articular "apparent" stiffness around the ankle joint is influenced by the magnitude of the impulse applied. Interestingly, this is driven by muscle stiffness, whereas tendon stiffness appears to be unaffected.

Menopause, estrogens and frailty

The controversy surrounding the results from the Women's Health Initiative (WHI) trials published a decade ago caused a significant decline in the use of menopausal hormone replacement therapy. However, these results have been vehemently contested and several lines of evidence suggest that in perimenopausal and non-obese women, estrogen therapy may indeed be of benefit. There is ample proof that menopause causes a loss of musculoskeletal tissue mass and quality, thereby causing a loss of health and quality of life. There is also solid evidence that hormone replacement therapy in itself prevents most of these effects in connective tissue in itself. Besides the independent, direct effects on the musculoskeletal tissues, estrogen deficiency also reduces the ability to adequately respond and adapt to external mechanical and metabolic stressors, e.g. exercise, which are otherwise the main stimuli that should maintain musculoskeletal integrity and metabolic function. Thus, normophysiological estrogen levels appear to exert a permissive effect on musculoskeletal adaptations to loading, thereby likely improving the outcome of rehabilitation following critical illness, musculoskeletal trauma or orthopedic surgical therapy. These effects add to the evidence supporting the use of estrogen therapy, particularly accelerated gain of functional capacity and independence following musculoskeletal disuse.

Assessing musculo-articular stiffness using free oscillations: theory, measurement and analysis

Stiffness, the relationship between applied load and elastic deformation, is an important neuromechanical component related to muscular performance and injury risk. The free-oscillation technique is a popular method for stiffness assessment. There has been wide application of this technique assessing a variety of musculature, including the triceps surae, knee flexors, knee extensors and pectorals. The methodology involves the modelling of the system as a linear damped mass-spring system. The use of such a model has certain advantages and limitations that will be discussed within this review. Perhaps the major advantage of such a model is the specificity of the measure, whereby it is possible for the assessment conditions to simulate the type of loading witnessed during functional tasks and sporting situations. High levels of reliability and construct validity have typically been reported using such procedures. Despite these assurances of accuracy, a number of issues have also been identified. The literature reveals some concerns surrounding the use of a linear model for stiffness assessment. Further, procedural issues surrounding the administration of the perturbation, attention focus of the participant during the perturbation, signal collection, data processing and analysis, presentation of stiffness as a linear or torsional value, assessment load (single vs multiple vs maximal) and the stiffness-load relationship have been identified, and are all fundamentally related to the quality of the calculated output data. Finally, several important considerations for practitioners have been recommended to ensure the quality and consistency of stiffness data collection, processing and interpretation.

Biomechanical properties of the triceps surae muscle-tendon unit in young and postmenopausal women

BACKGROUND

Insufficient and excessive stiffness may increase the risk of soft tissue and bone injuries, respectively, while the resonance frequency seems to be related with energy expenditure and stiffness. With aging and menopause muscle weakness, physical fragility and mobility limitations are also expected. Therefore this study addresses the differences of biomechanical properties of the triceps surae muscle-tendon unit between young and postmenopausal women.

METHODS

39 young and 37 postmenopausal women participated. The biomechanical properties of the triceps surae muscle-tendon unit were assessed in vivo using a free oscillation technique involving 30% of the maximal voluntary isometric contraction load.

FINDINGS

The postmenopausal women in this study show significant higher values in the damped natural frequency of oscillation (young 3.84Hz vs. postmenopausal 4.68Hz, P<0.001), muscle-tendon unit stiffness (young 16,446N/m vs. postmenopausal 23,229N/m, P<0.001), and muscle-tendon unit stiffness normalized by mass (young 286.3N/m vs. postmenopausal 325.1N/m, P<0.05). The postmenopausal study group shows significant lower values in the damping ratio (young 0.190 vs. postmenopausal 0.150, P<0.01) than young women.

INTERPRETATION

The postmenopausal subjects may not be able to take advantage of resonance as the young subjects, or, the relationship between these frequencies is adjusted according to the musculoskeletal characteristics of each group. The decrease in damping properties and the increase in muscle-tendon unit stiffness suggest that postmenopausal women might be at a greater risk of injury.