Sex differences in heel pad stiffness during in vivo loading and unloading

Due to conflicting data from previous studies a new methodological approach to evaluate heel pad stiffness and soft tissue deformation has been developed. The purpose of this study was to compare heel pad (HP) stiffness in both limbs between males and females during a dynamic unloading and loading activity. Ten males and 10 females volunteered to perform three dynamic trials to unload and load the HP. The dynamic protocol consisted of three continuous phases: foot flat (baseline phase), bilateral heel raise (unloading phase) and foot flat (loading phase) with each phase lasting two seconds. Six retroreflective markers (3 mm) were attached to the skin of the left and right heels using a customised marker set. Three-dimensional motion analysis cameras synchronised with force plates collected the kinematic and kinetic data throughout the trials. Three-way repeated measures ANOVA together with a Bonferroni post hoc test were applied to the stiffness and marker displacement datasets. On average, HP stiffness was higher in males than females during the loading and unloading phases. ANOVA results revealed no significant differences for the stiffness and displacement outputs with respect to sex, sidedness or phase interactions (p > .05) in the X, Y and Z directions. Irrespective of direction, there were significant differences in stiffness between the baseline and unloading conditions (p .116). Finally, females portrayed lower levels of mean HP stiffness whereas males had stiffer heels particularly in the vertical direction (Z) when the HP was both unloaded and loaded. High HP stiffness values and very small marker displacements could be valuable indicators for the risk of pathological foot conditions

Child transport practices and perceived barriers in active commuting to school

This study evaluated the transport practices of school children and perceived factors that influenced parental decisions regarding their child's use of active transport to commute to school. A self-administered parental questionnaire (n = 324) was used to determine the transport practices of school children and factors that influence parental decisions regarding their child's use of active transport to school. The relationship between transportation modes (active vs. passive), distance and descriptive variables were evaluated. Despite a median commuting distance of 2.5 km (0.1-28.0 km), only one-third of school trips involved active transport. Children using active transport commuted shorter distances (1.5 vs. 3.6 km), were older (10 vs. 8 years) and more likely to be male than those using motorised transport (P < 0.05). While logistic regression revealed only commuting distance was significantly associated with an increased odds of active transport (OR 0.29, 95% CI 0.17-0.48), the most frequently reported factors influencing parental decisions regarding their child's use of active transport were: (1) the age of child; (2) provision of safe walking paths; (3) adult supervision; (4) commuting distance, and (5) child's fitness level. While the majority of these factors have been identified within the literature, their validity has yet to be established

The effect of plantar fasciitis on vertical foot-ground reaction force

Despite the implication that mechanical overload is fundamental to the development of plantar fasciitis, gait analysis has revealed inconsistent findings regarding its effect on lower limb loading. The aim of the current study was to evaluate the regional vertical ground reaction force in patients with and without plantar fasciitis. A pressure platform was used to determine the vertical ground reaction force beneath the feet of 16 patients with, and an equivalent number of patients without, unilateral plantar fasciitis while completing 10 gait trials at a self-selected walking speed. The magnitude and timing of ground reaction force for the entire foot and for the regions of the rearfoot, midfoot, forefoot, and digits were measured for each limb. The findings indicate that patients with plantar fasciitis make gait adjustments that result in reduced force beneath the rearfoot and forefoot of the symptomatic foot. In addition, increased digital loading was observed in patients with plantar fasciitis suggesting that digital function plays an important, and previously unidentified, protective role

Frequency-domain analysis detects previously unidentified changes in ground reaction force with visually guided foot placement

Studies investigating the effect of targeting on gait have focused on the analysis of ground reaction force (GRF) within the time domain. Analysis within the frequency domain may be a more sensitive method for evaluating variations in GRF. The aim of the present study was to investigate the effect of visual targeting on GRF analyzed within the frequency domain. A within-subject repeated-measures design was used to measure the mediolateral, vertical, and antero-posterior components of the GRF of 11 healthy volunteers while walking at their own pace over a paper-covered walkway. A 30 x 24-cm target area was superimposed over a hidden Kistler force plate mounted at the midpoint of the walkway. GRF were recorded with and without the target and were analyzed within the frequency domain. Although visually guided foot placement has previously been undetected by traditional time-domain measures, targeting was found to significantly increase the frequency content of both the mediolateral (t10 = -4.07, p < 0.05) and antero-posterior (t10 = -2.52, p < 0.05) components of GRF. Consequently, it appears that frequency analysis is a more sensitive analytic technique for evaluating GRF. These findings have methodological implications for research in which GRF is used to characterize and assess anomalies in gait patterns

The development of a device to objectively measure knee joint stiffness

This paper discusses the development of a device to objectively measure knee joint stiffness. It was presented at the International Society of Biomechanics, XXII World congress, in 2009

Validation of the intensity of walking for pleasure in obese adults

Despite evidence that 'walking for pleasure' represents the most common leisure-time physical activity, the exercise intensity associated with 'walking for pleasure' in the obese has not been established. Heart rate (HR), perceived exertion (RPE) and walking speed were assessed for 30 obese and 20 non-obese adults as they completed two 2 km-walk tests on alternate days and were compared with a third 2 km walk with subjects walking 'as fast as possible'. Despite both obese (O) and non-obese (NO) groups rating the intensity of 'walking for pleasure' as 'light', HR and RPE data for only the NO group complied with definitions of 'light' intensity effort. 'Walking for pleasure' was characterised by a higher absolute (15 bpm, P < 0.05) and relative (70% of predicted maximum, P < 0.01) HR in the O group, which was representative of the transition between 'moderate' and 'hard' intensity exercise. The findings in the third, maximal trial were comparable across groups for all variables. Adiposity exerts a relative elevation-of-intensity effect on the cardiovascular system at walking speeds consistent with 'walking for pleasure'. 'Walking for pleasure' is sufficient to improve cardiovascular fitness in obese, but not normal-weight, individuals

Incidental walking activity is sufficient to induce time-dependent conditioning of the Achilles tendon

The Achilles tendon has been seen to exhibit time-dependent conditioning when isometric muscle actions were of a prolonged duration, compared to those involved in dynamic activities, such as walking. Since, the effect of short duration muscle activation associated with dynamic activities is yet to be established, the present study aimed to investigate the effect of incidental walking activity on Achilles tendon diametral strain. Eleven healthy male participants refrained from physical activity in excess of the walking required to carry out necessary daily tasks and wore an activity monitor during the 24 h study period. Achilles tendon diametral strain, 2 cm proximal to the calcaneal insertion, was determined from sagittal sonograms. Baseline sonographic examinations were conducted at approximately 08:00 h followed by replicate examinations at 12 and 24 h. Walking activity was measured as either present (1) or absent (0) and a linear weighting function was applied to account for the proximity of walking activity to tendon examination time. Over the course of the day the median (min, max) Achilles tendon diametral strain was -11.4 (4.5, -25.4)%. A statistically significant relationship was evident between walking activity and diametral strain (P<0.01) and this relationship improved when walking activity was temporally weighted (AIC 131 to 126). The results demonstrate that the short yet repetitive loads generated during activities of daily living, such as walking, are sufficient to induce appreciable time-dependant conditioning of the Achilles tendon. Implications arise for the in vivo measurement of Achilles tendon properties and the rehabilitation of tendinopathy

Modelling activity dependent diametral strain in Achilles tendon

The Achilles tendon is a viscoelastic tissue that typically experiences 3500 ± 1700 cyclic loads per day from intermittent periods of ambulatory activity. Typically, peak tensile loads exceed three times body weight and average about 1500 N during stance, which lasts for approximately 0.6 s, followed by a 0.2 s unloaded swing phase. Viscoelastic materials respond to external load (stress) in a time-dependent manner commonly referred to as creep deformation (strain) and recover slowly when unloaded. This can be observed in vivo by monitoring changes in tendon diameter using quantitative ultrasonography and is referred to here as diametral strain. Diametral strains between −25% and +10% have been recorded over a 24 h period and are hypothesised to be associated with fluid movement within the tendon that corresponds with the creep and recovery histories. Changes in tendon diameter were taken at five times throughout a 24 h period in 11 subjects. Ambulatory activity was monitored as time stamped cadence periods by a Polar RS800sd module enabling time of day and activity duration to be used as indicators of creep and recovery histories. These archival records of diametral strain versus activity were then used to develop an adaptive non-linear viscoelastic model for interpolating tendon cross-sectional dimensions between observation points and from which, site specific volumetric flow rates can be estimated. This model has an error bound of less than 5% and has the potential for application to future studies linking fluid flow within the tissue to inherent biomechanical properties, injury status or pathological defects

Tendon rehabilitation: isolated eccentric loading invokes a greater reduction in Achilles tendon thickness than concentric loading

Eccentric calf muscle exercise has been advocated as the treatment of choice in Achilles tendinopathy. However, mechanisms underlying the efficacy of eccentric, as opposed to concentric, exercise remain unknown. This research investigated the acute change in the sagittal thickness of the Achilles tendon (AT) in response to bouts of isolated eccentric or concentric calf muscle exercise. Eleven healthy males, without AT pathology (age, 25.9 ± 4.9 years; mass, 74.2 ± 11.8 kg), completed an exercise protocol involving isolated eccentric loading of the AT (ankle dorsi-flexion), while the contra-lateral AT experienced isolated concentric loading (ankle plantar-flexion). Six sets of 15 repetitions were performed against body weight, with an additional 20% bodyweight added via a backpack. AT thickness 2 cm proximal to the calcaneal insertion was determined from sagittal sonograms taken immediately prior to and following exercise. Consistent with earlier research, calf muscle exercise resulted in an abrupt decrease in AT thickness. However, isolated eccentric loading induced a significantly greater decrease (−20.8 ± 5.5%) than concentric loading (−5.3 ± 4.7%, p = 0.013). It is hypothesised that eccentric muscle action may invoke a differential stress field within the AT that results in a localised increase in collagen strain and extrusion of water from the tendon. Shear stress arising from such fluid flow may, in turn, stimulate tenocytes to produce matrix proteins that promote tendon remodelling, as has been shown in other collagen-rich tissues. The findings of this research have broad implications for the treatment of tendinopathy and provide greater insight into the clinically perceived benefit of eccentric over concentric exercise in AT rehabilitation