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.

Level of physical activity of students in Poland, Portugal and Belarus.

INTRODUCTION AND OBJECTIVE: The WHO term 'physical activity' refers to all body movements produced by skeletal muscles which require energy expenditure. The ways to be active include daily activities, exertion in the performance of work, or active recreation. The objective of the study is to compare physical activity of the students of Bialystok University of Technology, Higher School of Physical Education and Tourism in Biaystok (Poland), University of Beira Interior in Covilha (Portugal) and Janka Kupala Grodno State University in Grodno (Belarus). MATERIAL AND METHODS: A total of 1,136 persons participated in the study (398 men and 738 women). The level of physical activity of the students was assessed on the basis of a short version of the International Physical Activity Questionnaire (IPAQ). The individual value of the body mass index (BMI) was calculated for each respondent. RESULTS: Among men studying at WSWFiTB, in Portugal and Belarus, the dominant level of activity was high. Both in the group of men and women, people studying in Portugal spent the most time sitting during one working day. Without taking into account the gender of the respondents, a high level was the dominant among students of WSWFiTB, in Portugal and Belarus. With regard to overweight and obese people, the highest average amount of energy expenditure was recorded in the case of intensive activity. CONCLUSIONS: Men, compared to women, were characterized by a higher average amount of energy consumption related to total activity and intensive exercise. Students in Belarus obtained the highest average amount of energy expenditure related to moderate and intensive activity, compared to students at BUT, WSWFiTB and in Portugal. A high level of activity dominated both in the group of underweight/normal body weight, as well as overweight and obese persons.

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

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.

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 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.

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.