The effect of a specific fatigue protocol in force propulsion and postural sway in female handball athletes

Fatigue is a case of interaction between different factors and is characterized by the increase in the perceived effort to exercise and produce force. However, the effect on balancing tasks are not completely understood, especially the time course of the postural sway parameters during the recovery phase. Twenty female handball athletes participated in this study. They stood upright in a one-leg posture supported by the non-dominant limb on a force plate. The center of pressure (COP) and the maximum propulsion force (FMAX) were obtained at baseline, immediately after the exhaustion due to the fatigue protocol and every minute during the first 10 min of the recovery phase. For the postural-sway measures, participants stood on the force plate for 30 s with eyes opened looking to a target. Based on the COP displacement, the ellipse area containing 95% of the COP data points (Area) was computed. The FMAX was measured during a countermovement jump. Specific handball actions composed the fatigue protocol in the format of a circuit with the gradual increment of laps. The force decreased ~9.5% after the fatigue protocol (p = 0.01) and returned to baseline values during the recovery phase at the fifth minute. For the postural sway, the Area decreased during the recovery phase until the fourth minute (p = 0.007). The fatigue protocol affected postural sway and force variables, which returned to baseline values after four minutes of the protocol. Therefore, we suggest that future fatigue analyses should be tested during this time window.
Listed In: Biomechanics, Posturography, Sports Science


While the popularity of triathlon is increasing, the underlying biomechanics of the various bicycling positions and saddle types are not yet understood. PURPOSE: To determine how bicycle rider position and saddle type (road vs. triathlon) affect the bicycle-rider interface forces (BRIFs) at a standardized power and cadence. METHODS: A stationary cycling ergometer was modified to include force transducers at the saddle, bottom bracket, and stem. Anatomical measurements were made in order to fine-tune rider fit on the ergometer. 9 subjects completed riding trials in all combinations of road position, road saddle, triathlon position, and triathlon saddle. Riding trials were 6 minutes, at a standardized power output of 2 Watts per kilogram (W/kg) and 90 Revolutions per Minute (RPM). RESULTS: Analysis was broken into three categories: Road Saddle, Road Position (RR) vs. Triathlon Saddle, Road Position (TR), Road Saddle, Triathlon Position (RT) vs. Triathlon Saddle, Triathlon Position (TT), and Road Saddle, Road Position vs. Triathlon Saddle, Triathlon Position. Surprisingly, there were no significant differences in saddle vertical forces between either body positions or saddle type. However, there were significant differences at the handlebar; 8.4% more body weight supported at the handlebar in the triathlon position compared to the road position while using a triathlon saddle. CONCLUSION: Across cycling positions, there is a significant change in saddle and stem vertical forces. However, within a cycling position, saddle type does not change the amount of vertical force seen at the saddle.
Listed In: Biomechanical Engineering, Biomechanics, Sports Science

Effects of cortical stimulation on sensorimotor hand functions in healthy elderly individuals

Transcranial anodal stimulation (tDCS) improves manual dexterity in healthy old adults. The underlying changes in finger force behavior for this improved dexterity have not been reported. Here, we investigated the effects of tDCS (20-min) over primary motor cortex (M1) combined with repeated practice on the Grooved pegboard test (tDCS+MP) on the fingertip forces applied to an object during grasp and manipulation. Eight right-handed able-bodied individuals (60-85 years) participated in a sham-controlled, single-blinded study. Each participant received anodal and sham intervention in two sessions at least 5-day apart. Before and after intervention, they performed a ‘key-slot’ task that required inserting a slot on an object onto a stationary bar, an isometric force production task using a pinch grip, and the Grooved pegboard test. Anodal relative to sham tDCS+MP allowed participants to better retain the improved performance on the pegboard test. For the isometric task, anodal tDCS+MP significantly increased the variability of force compared to sham tDCS+MP. More importantly, the improved retention of performance post-anodal tDCS correlated with the reduction in force angle variability on the key-slot task, but not with the change in force variability on the isometric task. Our findings suggest that anodal tDCS+MP facilitated retention of learning on a skillful manual task in healthy old adults, consistent with the role of M1 in retention of learning versus skill acquisition. Furthermore, improved force steadiness is one of the potential mechanisms through which short-term anodal tDCS during motor training yields improved performance on a functional task.
Listed In: Biomechanics, Neuroscience