João Abrantes

Dynamic joint stiffness of the ankle during walking: Gender-related differences

OBJECTIVES To characterize and compare dynamic joint stiffness (DJS) of the ankle in the sagittal plane during natural cadence walking in both genders. DESIGN Observation, cross-sectional and matched pairs. PARTICIPANTS Twenty-one males (mean age=27+/-4.2 years) and 18 females (mean age=22.9+/-4.1 years). SETTING Laboratory at the University de Trás-os-Montes and Alto Douro. The DJS of the ankle was assessed while participants performed barefoot walking at a natural cadence, was measured using a force platform (1000 Hz), and synchronized with a high-speed camera (200 Hz). MAIN OUTCOME MEASURES DJS of the ankle in males and females was calculated in two sub-phases (the second and the fourth sub-phases) of the stance phase. The Wilcoxon non-parametric matched-pairs test and the Mann-Whitney U non-parametric test were used to analyse difference of DJS of the ankle within and between the groups with p0.05 regarded as significant. RESULTS Male and female participants demonstrated significantly (p<0.005) less DJS during the second sub-phase. DJS was not significantly (p>0.063) different between females (0.0511 N m/kg/ degrees ) and males (0.0596 N m/kg/ degrees ) during the second sub-phase. DJS was significantly (p<0.001) higher in males (0.0844 N m/kg/ degrees ) than females (0.0691 N m/kg/ degrees ) during the fourth sub-phase. CONCLUSIONS Gender-specific DJS characteristics demonstrated by females in this study may be used in preventative training programs designed to promote a greater ability to use contractile components to produce mechanical energy through the ankle.

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.

Spatial reconstruction of human motion by means of a single camera and a biomechanical model

The value of the results of the inverse dynamic analysis procedures used in the study of human tasks is dependent on the quality of the kinematic and kinetic data supplied to the biomechanical model that supports it. The kinematic data, containing the position, velocity and acceleration of all anatomical segments of the biomechanical model, result from the reconstruction of human spatial motion by means of the evaluation of the anatomic points positions that enable to uniquely define the position of all anatomical segments. Furthermore, the motion data must be kinematically consistent with the structure of the biomechanical model used in the analysis. The traditional photogrammetric methodologies used for the spatial reconstruction of the human motion require images of two or more calibrated and synchronized cameras. This is due to the fact that the projection of each anatomical point is described by two linear equations relating its three spatial coordinates with the two coordinates of the projected point. The need for the image of another camera arises from the fact that a third equation is necessary to find the original spatial position of the anatomical point. The methodology proposed here substitutes the projection equations of the second camera with the kinematic constraint equations associated with a biomechanical model in the motion reconstruction process. In the formulation the system of equations arising from the point projections and biomechanical model kinematic constraints, representing the constant length of the anatomical segments, are solved simultaneously. Because the system of equations has multiple solutions for each image, a strategy based on the minimization of a cost function associated to the smoothness of the reconstructed motion is devised. It is shown how the process is implemented computationally avoiding any operator intervention during the motion reconstruction for a given time period. This leads to an automated computer procedure that ensures the uniqueness of the reconstructed motion. The result of the reconstruction process is a set of data that is kinematically consistent with the biomechanical model used. Through applications of the proposed methodology to several sports exercises its benefits and shortcomings are discussed.

Spatial reconstruction of the human motion based on images of a single camera

The inverse dynamic analysis procedures used in the study of the human gait require that the kinematics of the supporting biomechanical model is known beforehand. The first step to obtain the kinematic data is the reconstruction of human spatial motion, i.e., the evaluation of the anatomic points positions that enables to uniquely define the position of all anatomical segments. In photogrammetry, the projection of each anatomical point is described by two linear equations relating its three spatial coordinates with the two coordinates of the projected point. The need for the image of two cameras arises from the fact that three equations are necessary to find the original spatial position of the anatomical point. It is shown here that the kinematic constraint equations associated with a biomechanical model can be used as the extra set of equations required for the reconstruction process, instead of the equations associated with the second camera. With this methodology, the system of equations arising from the point projections and biomechanical model kinematic constraints are solved simultaneously. Since the system of equations has multiple solutions for each image, a strategy based on the minimization of the cost function associated to the smoothness of the reconstructed motion is devised, leading to an automated computer procedure enabling a unique reconstruction.

Estimation of the muscle force distribution in ballistic motion based on a multibody methodology

This work presents a general three-dimensional multibody procedure for studying the human body motion with emphasis on the locomotion apparatus. The methodology includes a three-dimensional biomechanical model, data acquisition techniques and an inverse dynamics approach. The biomechanical model is based on a multibody formulation using natural coordinates and consists of 16 anatomical segments modeled by 33 rigid bodies for a total of 44 degrees-of-freedom. The action of the muscles is introduced in the equations of motion of the multibody model by means of driver actuators defined as kinematic constraints. By associating a Lagrange multiplier to each muscle actuator the muscle forces became coupled with the biomechanical model through the Jacobian matrix of the underlying multibody system. A Hill type muscle model is used to calculate individual muscle forces. The model for the muscle apparatus comprises 43 muscle groups for each leg, which use the full three-dimensional lines of action for these muscles in their geometric description. The problem of the redundancy of the forces on the musculoskeletal structure is solved by using inverse dynamics and static optimization methods. In the process of describing the methodology the benefits of modeling in natural coordinates are highlighted. The methodology developed is demonstrated through its application to a case of ballistic motion, represented by the take-off to an aerial trajectory in order to estimate the joint torques and the muscle force distribution in the supporting leg. The time characteristics of the resultant net torques at the basic joints of the supporting leg and the time-varying muscle force patterns are presented and discussed. The results obtained are explained in terms of their relevance to the activity under study.

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.

Exercise effects in plantar pressure of postmenopausal women.

Objective: The aim of this study was to investigate the effect of a 12-month moderate-to-vigorous exercise program on plantar pressure among postmenopausal women. Methods: A total of 121 white postmenopausal women participated in a randomized controlled trial (60 women in the exercise group and 61 women in the control group). Women in the exercise group attended training sessions of 60 minutes, 3 days per week, on nonconsecutive days. Weight and basal metabolic rate were evaluated by bioimpedance, and height was evaluated with a stadiometer. Plantar pressure data were collected using the Footscan platform and Software 7.1. Results: After the 1-year intervention, women from the exercise group had (1) lower body mass index, (2) equal basal metabolic rate, (3) lower peak pressures, and (4) lower absolute impulses compared with the women from the control group. Interaction between the exercise group and practice time was found for most of the maximal peak pressure areas (except for metatarsal 4), for all absolute impulse values, and for relative impulses in the hallux, metatarsal 4, midfoot, and medial heel. Conclusions: This study seems to prove that women who exercise have decreased loading of maximal peak pressures and absolute impulses and, consequently, self-reported pain, soreness, and discomfort in the lower extremity. An interaction effect between group and practice time was found for most of the variables considered, meaning that this 12-month exercise program is effective in the improvement of the biomechanic parameters of plantar pressure.

Impact of a 12-month exercise program on the temporal parameters of the foot rollover during walking in postmenopausal women.

Objective: A randomized controlled trial was undertaken to determine the impact of a 12-month exercise program on the temporal characteristics of the foot rollover during walking, based on plantar pressure data. Methods: One hundred twenty one postmenopausal women aged 41 to 77 years comprised the sample and were randomly recruited from the community. Exercise and control women were tested before and at the end of the trial. The temporal characteristics were assessed with the women walking barefoot at a self-selected speed over a 9-meter-long walking track having a built-in pressure platform. The initial and final contacts at the lateral and medial heel, metatarsal heads I to V, and the hallux (medial and lateral) were measured. Results: Women from the exercise group presented a latter time of making contact in the relative metatarsal 4, metatarsal 5 (absolute and relative), and medial heel (absolute and relative) and earlier relative initial contact in toe 1. In the modification rates, postmenopausal women from the exercise group presented (1) latter final contact (absolute and relative) in metatarsal 5, (2) latter relative final contact in metatarsal 4, and (3) earlier relative initial contact in toe 1. Postmenopausal women from the control group presented an earlier initial contact in metatarsal 3 (absolute and relative). Repeated-measures analysis of variance demonstrated a time effect in most variables considered. Conclusions: The exercise program is effective in improving the gait pattern in postmenopausal women who adhere, and time has the main effect.

Influence of Footedness on Dynamic Joint Stiffness during the Gait Stance Phase

Aims: Dynamic joint stiffness (DJS) is used as a joint stability indicator. The objective of the present study is to verify the influence of footedness in ankle joint stability during the gait stance phase. Study Design: Comparative study. Place and Duration of Study: MovLab/ CICANT/ Universidade Lusofona de Humanidades e Tecnologias, between November 2013 and June 2014 Methodology: 31 subjects (20 female and 11 male) presenting different footedness (right and left) were assessed. Ten gait stance phase trials (five each side) were recorded using a 3D motion capture system and a force platform. Synchronized ankle sagittal moment of force and angular position were used to calculate DJS for three defined sub-phases of gait stance phase: controlled Original Research Article Atalaia et al.; JSRR, 5(2): 175-183, 2015; Article no.JSRR.2015.085 176 plantar flexion, controlled dorsiflexion and powered plantar flexion. Mann-Whitney U test was calculated to assess footedness influence on biomechanical variables. Results: No significant differences were found between dominant and non-dominant limb in different combinations of footedness and gender. Conclusion: Footedness do not seem to influence DJS and consequent joint stability. Observing the trials per participant, differences can be noted but commonly used statistical approach cannot highlight those differences. Further studies should address ankle frontal plane behaviour or assess differences at the knee and hip joints, as they could present more differences that could be statistically significant.