Effects of exercising with a weighted vest on the output of lower limb joints in countermovement jumping

The effect of exercising with a weighted vest equal to 15% of body mass on vertical jump height was assessed. It was hypothesized that the defined treatment protocol could enhance jumping performance by increasing hip, knee and ankle joint power. The findings of this study showed that the defined active stretching protocol significantly increases jump height in male participants (0.3364 m compared to0. 3456 m from pre to post exercise respectively) but did not yield a significant increase in females. No significant changes in joint angle, torque, power or velocity were observed between the pre and post exercise jumping. However, the pre-take off phase of jumping was significantly decreased after the exercise. Also a significant increase in the initial velocity was observed in the post loaded jumping in men (2.507 m/s Vs. 2.588 from pre to post exercise respectively). Analysis of jumping with the weighted vest revealed numerous significant changes in temporal aspects of jumping as well as joint output. It was observed that performing the weighted jumping for five sets of three repetitions, could increase the jump height which was originally decreased by applying the vest. Findings of the analysis of jumping with the weighted vest and those of jumping after the removal of the vest did not support the increase of a specific parameter for a specific joint. Rather, it suggests that the application of this treatment increases the performance by optimizing the timing of various movement sequences

A novel therapy to regain control of spinal motoneurons in stroke survivors

Thesis (Ph.D.) - Indiana University, School of Public Health, 2014The purpose of this research was to demonstrate that hemiplegic stroke survivors possess the ability to modulate their H-reflex amplitude through exercise induced operant conditioning. To better understand the changes in the spinal cord associated with hemiplegic stroke, two important inhibitory spinal cord mechanisms, namely post activation depression (PAD) and Group I reciprocal inhibition (RI) were also examined. Examining PAD with conditioning-test intervals between 80 to 300 ms showed a substantial depression in the amplitude of the H-reflex in healthy individuals. In stroke patients there was significantly less inhibition at all intervals, with full recover of the H-reflex at the 300 ms interval. In healthy individuals conditioning the soleus H-reflex with common peroneal nerve stimulation caused an initial inhibitory phase at about 10 ms interval (D1 inhibition) and a second phase of inhibition at longer intervals (> 100 ms; D2 inhibition). In stroke patients, no statistically significant inhibition was observed, although partial interaction analysis suggested that D1 inhibition followed a pattern similar to that of healthy individuals. Finally, a three-week exercise induced operant conditioning program was examined in three stroke patients. All patients demonstrated success for down-regulating the amplitude of the soleus H-reflex. More importantly, after training all subjects demonstrated improvements in gait parameters. It is concluded that spinal cord inhibitory mechanisms are different between healthy controls and stroke patients, and that exercise induced operant conditioning is a promising method for regaining functional control of motoneurons

Transspinal Direct Current Stimulation Produces Persistent Plasticity in Human Motor Pathways

The spinal cord is an integration center for descending, ascending, and segmental neural signals. Noninvasive transspinal stimulation may thus constitute an effective method for concomitant modulation of local and distal neural circuits. In this study, we established changes in cortical excitability and input/output function of corticospinal and spinal neural circuits before, at 0–15 and at 30–45 minutes after cathodal, anodal, and sham transspinal direct current stimulation (tsDCS) to the thoracic region in healthy individuals. We found that intracortical inhibition was different among stimulation polarities, however remained unchanged over time. Intracortical facilitation increased after cathodal and anodal tsDCS delivered with subjects seated, and decreased after cathodal tsDCS delivered with subjects lying supine. Both cathodal and anodal tsDCS increased corticospinal excitability, yet facilitation was larger and persisted for 30 minutes post stimulation only when cathodal tsDCS was delivered with subjects lying supine. Spinal input/output reflex function was decreased by cathodal and not anodal tsDCS. These changes may be attributed to altered spontaneous neural activity and membrane potentials of corticomotoneuronal cells by tsDCS involving similar mechanisms to those mediating motor learning. Our findings indicate that thoracic tsDCS has the ability to concomitantly alter cortical, corticospinal, and spinal motor output in humans

Disturbances of postural sway components in cannabis users

Introduction A prominent effect of acute cannabis use is impaired motor coordination and driving performance. However, few studies have evaluated balance in chronic cannabis users, even though density of the CB1 receptor, which mediates the psychoactive effects of cannabis, is extremely high in brain regions critically involved in this fundamental behavior. The present study measured postural sway in regular cannabis users and used rambling and trembling analysis to quantify the integrity of central and peripheral nervous system contributions to the sway signal. Methods Postural sway was measured in 42 regular cannabis users (CB group) and 36 non-cannabis users (N-CB group) by asking participants to stand as still as possible on a force platform in the presence and absence of motor and sensory challenges. Center of pressure (COP) path length was measured, and the COP signal was decomposed into rambling and trembling components. Exploratory correlational analyses were conducted between sway variables, cannabis use history, and neurocognitive function. Results The CB group had significantly increased path length and increased trembling in the anterior-posterior (AP) direction. Exploratory correlational analyses suggested that AP rambling was significantly inversely associated with visuo-motor processing speed. Discussion Regular cannabis use is associated with increased postural sway, and this appears to be predominantly due to the trembling component, which is believed to reflect the peripheral nervous system’s contribution to the sway signal

The force applied to the knee extensor mechanism differs between flat-footed and normal subjects during walking

Study aim: There is a lack of evidence to show the presence or absence of a relationship between foot morphology and changes of the force applied to the knee extensor mechanism. The purpose of this study was to examine whether the type of foot is a determining factor in the force applied to the extensor mechanism during walking. Materials and methods: Twenty female subjects (18-30 years), 10 with neutrally aligned feet and 10 with functional flat foot, participated in this study. Data were collected by employing a three dimensional motion capture system and a force platform, while the subjects were walking at their preferred speed. Knee extensor mechanism force was measured at sub-phases of gait (heel strike and toe-off). Results: A significant interaction was found between groups and sub-phases of gait for all the variables tested. The subjects with flat foot exhibited a significantly higher extensor mechanism force at toe-off compared to the control group (p < 0.05). Conclusion: It can be concluded that subtalar hyper-pronation would increase the force applied to the knee extensor mecha­nism at toe-off, through increasing the knee sagittal angle, net external flexion moment and extensor mechanism moment arm. Therefore it may increase the possibility of musculoskeletal injurie

A Biomechanical Analysis of the Contributing Factors to Increases in Vertical Jump Height Following Exercise with Weighted Vests

Background: It has been shown that a bout of jumping exercise with weighted vests increases the subsequent countermovement jump height. However, it is not clear whether the improvement in jump height is due to the enhancement of joint power or due to other mechanisms such as neural adaptations. Methods: To investigate this dichotomy, we tested the acute neuromechanical changes following a preloaded exercise protocol (3 sets of 5 consecutive CMJs with a weighed vest equal to 15% of the body mass of the participant) that successfully increased the subsequent jump height. On average, jump height increased 1.52 cm (5.40%) after this exercise as compared to CMJs prior to the exercise protocol. Results: A significant decrease in the time from the start of the movement to take off (pre-take off duration) was observed. This decrease was exclusively caused by exercising with a weighted vest, since such a change was not observed in the control sessions in which participants exercised without the weighted vest. Our data showed that jumpers leave the ground with some degrees of knee flexion and upon exercising with weighted vest this amount of flexion increased and hence an increase in the jump height. However, no significant changes in peak values of lower limb joint angle, velocity, moment and power were observed. Conclusion: It is suggested that for designing weighted vest exercise protocols with the aim of increasing jump height, the idea of modifying the timing of the movement should be considered as a cause of the enhancement. This novel idea adds another mechanism for increasing the jump height following weighted vest exercise, along with the general belief of muscle potentiation