The ability to move and maintain posture is critically dependent on motion and orientation information provided by the vestibular system. When this system delivers noisy or erred information it can, in some cases, be attenuated through habituation. Here we investigate whether multiple mechanisms of attenuation act to decrease vestibular gain due to noise added using supra-threshold random-waveform galvanic vestibular stimulation (GVS). Forty-five participants completed one of three conditions. Each condition consisted of two 4-min standing periods with stimulation surrounding a 1-h period of either walking with stimulation, walking without stimulation, or sitting quietly. An instrumented treadmill recorded horizontal forces at the feet during standing and walking. We quantified response attenuation to GVS by comparing vestibular stimulus-horizontal force gain between conditions. First stimulus exposure caused an 18% decrease in gain during the first 40 s of standing. Attenuation recommenced only when subjects walked with stimulation, resulting in a 38% decrease in gain over 60 min that did not transfer to standing following walking. The disparity in attenuation dynamics and absent carry over between standing and walking suggests that two mechanisms of attenuation, one associated with first exposure to the stimulus and another that is task specific, may act to decrease vestibulomotor gain.

The aims of this study were twofold: 1) to examine lower extremity coordination during bodyweight squats performed at two different tempos, and 2) to establish a reliable measure of segment coordination variability. Eighteen subjects (10 F, 8 M) completed bodyweight squats at preferred (self-paced) and non-preferred (metronome-paced) tempos. A modified vector coding approach used kinematic data to compute absolute couplings patterns and coordination variability for three couplings (foot-shank, shank-thigh, thigh-trunk) in three planes of motion for the descent and ascent phases of a squat cycle. A coordination variability reliability equation was used to determine the number of squats needed for a reliable index of movement variability relative to total variability over 20 squats. Tempo did not significantly alter the absolute coordination patterns of any couplings. The reliability equation revealed that 5–9 squats were needed for a reliable coordination variability measure. Nine squats provided a reliable measure of coordination that is comparable to using 20 double leg squats in the calculation. Using nine squats ensures reliable calculations in the frontal, sagittal and transverse planes at preferred and non-preferred speeds. These results can be used to guide clinical evaluation of acceptable levels of movement variability during rehabilitation.

The vestibular system encodes motion and orientation of the head in space and is essential for negotiating in and interacting with the world. Recently, random waveform electric vestibular stimulation has become an increasingly common means of probing the vestibular system. However, many of the methods used to analyze the behavioral response to this type of stimulation assume a linear relationship between frequencies in the stimulus and its associated response. Here we examine this stimulus-response frequency linearity to determine the validity of this assumption. Forty-five university-aged subjects stood on a force-plate for 4 min while receiving vestibular stimulation. To determine the linearity of the stimulus-response relationship we calculated the cross-frequency power coupling between a 0 and 25 Hz bandwidth limited white noise stimulus and induced postural responses, as measured using the horizontal forces acting at the feet. Ultimately, we found that, on average, the postural response to a random stimulus is linear across stimulation frequencies. This result supports the use of analysis methods that depend on the assumption of stimulus-response frequency linearity, such as coherence and gain, which are commonly used to analyze the body’s response to random waveform electric stimuli.

Background Performance asymmetries between the lower limbs have been reported across a variety of variables and for numerous motor tasks including double leg squats. Additionally, the degree of symmetry is often used as a recovery metric during rehabilitation programs. Hypothesis/Purpose The purpose of this investigation was to examine leg asymmetry during a bodyweight double leg squat task and assess the effects of squat speed in a physically active population. Study Design Cross-over Study Design. Methods Eighteen healthy individuals completed two sets of 20 squats at two tempos (preferred tempo and 60 bpm) while ground reaction force and center of pressure data were recorded using dual force plates. Peak vertical ground reaction force, force impulse, and center of pressure (COP) standard deviation in the anterior-posterior (AP) and mediolateral (ML) direction were calculated and analyzed to identify any differences between legs, tempo, and as a function of repetitions. Significance was set at ρ ≤ .05. Results The subjects exhibited greater ground reaction forces during the self-paced tempo compared to the metronome-paced tempo (F1,79 = 14.48, p < .001) with the preferred leg generating larger values than the non-preferred leg during the self-paced condition. There was also a significant tempo x leg interaction for force impulse (F1,79 = 5.927, p = 0.015). A greater amount of COP variability was found in the preferred leg compared to the non-preferred leg in both the AP (F1,79 = 30.147, p < 0.001) and ML (F1,79 = 41.204, p < 0.001) directions. Conclusions These findings highlight the importance of considering multiple levels of analysis when assessing lower limb symmetry as separate variables may provide differential evidence for asymmetry. Practically, these results emphasize the need for coaches and practitioners to consider different degrees of lower limb asymmetries that may impact the development and design of strength and rehabilitation programs. Level of Evidence 3