Rui Brás

Triceps-surae musculotendinous stiffness: relative differences between obese and non-obese postmenopausal women.

BACKGROUND There is a lack of research into the relationship between obesity and muscle-tendon unit stiffness in postmenopausal women. Muscle-tendon unit stiffness appears to affect human motion performance and excessive and insufficient stiffness can increase the risk of bone and soft tissue injuries, respectively. The aim of this study was to investigate the relationship between muscle-tendon unit stiffness and obesity in postmenopausal women. METHODS 105 postmenopausal women (58 [SD 5.5] years) participated. Four groups (normal weight, pre-obese, obesity class I and obesity class II) were defined according World Health Organization classification of body mass index. The ankle muscle-tendon unit stiffness was assessed in vivo with a free oscillation technique using a load of 30% of maximal voluntary isometric contraction. FINDINGS ANOVA shows significant difference in muscle-tendon unit stiffness among the groups defined (P<0.001). Post hoc analysis reveals significant differences between the following groups: normal weight-pre-obese; normal weight-obesity class I and normal weight-obesity class II. The normal weight group had stiffness of 15789 (SD 2969) N/m, pre-obese of 19971 (SD 3678) N/m, obesity class I of 21435 (SD 4295) N/m, and obesity class II of 23497 (SD 1776) N/m. INTERPRETATION Obese subjects may have increased muscle-tendon unit stiffness because of fat infiltration in leg skeletal muscles, range of motion restrictions and stability/posture reasons and might be more predisposed to develop musculoskeletal injuries. Normal weight group had identical stiffness values to those reported in studies where subjects were not yet menopausal, suggesting that stiffness might not be influenced by menopause.

The relationship of body mass index, age and triceps-surae musculotendinous stiffness with the foot arch structure of postmenopausal women.

BACKGROUND Low- or high-arched feet and insufficient or excessive muscle-tendon stiffness have been identified as risk factors for lower extremity injuries. Additionally, increased body mass index and age may be responsible for structural changes of the foot, which might adversely affect the functional capacity of the longitudinal arch. Therefore, the aim of this study was to investigate the relationship of body mass, age and triceps-surae musculotendinous stiffness with the foot arch structure of postmenopausal women. METHODS 81 post menopausal women (58.0 (SD 6.0) years) participated. An in vivo free oscillation technique was used to assess musculotendinous stiffness of the ankle. The two-step protocol was used to acquire gait plantar pressure data. Dynamic arch index was calculated as the ratio of the midfoot area to the area of the entire foot excluding the toes. Three groups were formed (cavus, normal and planus). FINDINGS Significant differences (P<0.05) between the groups cavus and planus were found for age using the ANOVA test. Using Kruskal-Wallis tests significant differences were found for body mass index between the cavus-normal groups and cavus-planus (P<0.001) but no significant differences were found for triceps-surae musculotendinous stiffness between foot-type groups. INTERPRETATION Since obese subjects present greater downward vertical forces, they might be more prone to overload foot structures leading to the collapse of the medial longitudinal arch affecting adversely the functional capacity of the foot. Deterioration of the musculoskeletal system, due to age, may also affect foot arch structure. No relationship between musculotendinous stiffness and foot arch structure appears to exist.

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.

The effect of sex and localised fatigue on triceps surae musculoarticular stiffness

Abstract Purpose: The main purpose of this study was to investigate the influence of fatigue on musculoarticular stiffness (MAS) of the ankle joint across sexes. Methods: Twenty-seven males and 26 females participated in the study. After baseline assessment of MAS and related variables, localised fatigue was induced in triceps surae using the standing heel-rise test during which the subjects were instructed to lift and drop the heel at a frequency of 0.5 Hz. When subjects were unable to continue due to exhaustion the test was terminated and another MAS test was performed soon after. Results: Significant higher triceps surae MAS was found in men compared to women (p < .01). MAS decreased (p < .01) between pre- and post-fatigue on average from 18.0 to 17.0 KN m−1 and from 14.5 to 13.9 KN m−1 in men and women, respectively. Percentage changes revealed, however, that in relative terms the changes in all the variables evaluated were similar (p > .01) between sexes, with MAS less than 5%. Conclusion: Despite the sex-related differences at baseline, fatigue seems to affect biomechanical properties of the ankle joint similarly in men and women.

Musculo-articular stiffness is affected by the magnitude of the impulse applied when assessed with the free-oscillation technique.

Musculo-articular stiffness (MAS) of the triceps surae can be assessed using the free-oscillation technique whereby an impulse is applied and the ensuing damped oscillations are recorded. The purpose of this study was to investigate if impulses of different magnitudes can affect the measurement of MAS. Twenty seven males (20.7±1.3 years) participated in this study. Three impulses of different magnitude (1.5, 2.3 and 3.1Ns) and four different loads (10, 20, 30, 40kg) were employed in the assessment of triceps surae MAS, which was quantified and compared across loads and perturbations. As the magnitude of the impulse applied increased, the MAS (p<0.0005, ES 1.20) and natural frequency of oscillation (f) decreased while the amplitude of movement (AM), angular velocity (ω) and damping coefficient (C) increased significantly. As the load level increased, the MAS (p<0.0005, ES 2.25) and the baseline ground reaction force (BGRF) increased whereas f, AM and ω decreased significantly. Even though the effect of the load is stronger, it appears that the level of MAS recorded (ranging from 24.0 to 21.3KN/m for the 10kg load and from 32.9 to 31.0KN/m for the 40kg load, for impulse 1 and 3 respectively), including several underlying factors, are affected by the magnitude of the impulse, therefore its accurate determination is pivotal. Caution should be exercised when comparing results from previous studies where the magnitude of the impulse has only been estimated but not controlled for.

Application of Thermal Imaging and PWC170 Test for the Evaluation of the Effects of a 30-Week Step Aerobics Training

Abstract The aim of this paper is to verify whether step aerobics training (SAT) has an impact on the temperature of deep muscles of the spine of young, healthy subjects and if there exists a relationship between the maximal oxygen uptake (VO2max) and thermal results. The study was conducted in a group of 21 subjects of both sexes, aged 20.2 ± 0.38. The step aerobics training sessions lasted 30 weeks, one training session per week, 60 minutes per session. Thermograms of the spine were taken with the use of an infrared thermographic camera. Instrumental measurements included BMI, vital capacity of the lungs, and maximal oxygen uptake (VO2max). After a 30-weeklong SAT, a statistically significant increase in the average temperature of the muscles of the thoracic and lumbar spine was observed in subjects of both sexes (1.2◦C and 1.28◦C, respectively, p < 0.05). At the same time, VO2max increased from 42.98 ml/kg/min to 43.6 ml/kg/min in male subjects and from 40.4 ml/kg/min to 41.1 ml/kg/min in female subjects (p > 0.05). The relationship between VO2max and temperature of the muscles of the thoracic and lumbar spine after the 30th SAT was not statistically significant (r = - 0.28; p = 0.226; r = - 0.11; p = 0.634, respectively). The study showed that a 30-weeklong step aerobics training (SAT) had a positive impact on thermoregulation of apparently healthy male and female subjects aged 20. Furthermore, it can be safely assumed that thermography may be used as a non-invasive method of examination of the thermoregulation mechanism of SAT participants.