Andrew L. McDonough

The effects of joint angle on electromyographic indices of fatigue

The purpose of this study was to examine the effect of manipulation of joint angle on electromyographic (EMG) fatigue curves at different sites over the quadriceps muscle group. Eight subjects performed isometric knee extensions at 0.26, 0.79, and 1.31 rad from full extension for 1 min at 50% of maximum. EMG signals were recorded with a branched electrode lead system at proximal and distal sites over the vastus lateralis and vastus medialis. The 1-min contractions were analyzed for changes in integrated EMG (IEMG) and median power frequency (MPF) over time. The results showed that the fatigue slopes for IEMG were greatest at 0.79 rad. However, the MPF data showed the greatest slopes at 0.26 rad. We hypothesize that the decline in MPF at 0.26 rad is due to activation failure while the increase in IEMG at 0.79 rad is driven by contractile failure. In addition, the EMG fatigue rates within each joint angle were similar at all sites.

Coordination variability during load carriage walking: Can it contribute to low back pain?

Load carriage walking is frequently associated with low back pain. Mechanical stress is a potential cause of such pain, and a lack of coordination variability may produce mechanical stress. We tested the hypothesis that coordination variability would decrease during load carriage walking. We examined the trunk-thigh coordination variability in the sagittal and frontal planes and the thorax-pelvis coordination variability in the transverse plane. Ten healthy participants were recruited to perform unloaded and load carriage walking. Coordination variability was quantified as the standard deviation of continuous relative phase between two segments across a number of walking trials. During load carriage walking, the coordination variability significantly increased rather than decreased in the sagittal and transverse planes, and it did not change significantly in the frontal plane compared to those during unloaded walking. The findings rejected the hypothesis and suggested that reduced coordination variability may not predict the development of low back pain associate with load carriage walking in healthy people.

Temporal relationship between trunk and thigh contributes to balance control in load carriage walking

Load carriage walking (LCW) challenges a persons balance as the load increases their forward trunk inclination, shifting the center of mass (COM) forward with respect to the base of support (BOS). We examined LCW to understand whether and how healthy people adjust the temporal relationship (TR) between the trunk and leg for balance control. Ten subjects were recruited to perform unloaded walking and LCW. The TR between the trunk and leg was measured by the continuous relative phase. The maximum forward displacement of the COM with respective to the BOS (FDCOM(BOS)) was recorded during the stance phase. We found that the TR was shifted in LCW, and the shift was associated with a decrease in the maximum FDCOM(BOS). The findings suggest that the TR between the trunk and leg contributes to balance control, and it may be a variable that needs to be addressed in gait rehabilitation.

Evaluation of the cushion setting on performance of a Biodex II dynamometer.

OBJECTIVES To compare the effects of the soft cushion setting with those of the hard cushion setting of a Biodex II isokinetic dynamometer on peak velocity and peak torque with six loads at 23 preset speeds. DESIGN Mixed within- and between-groups, repeated-measures design. SETTING Research laboratory of a physical therapy education program. INTERVENTIONS Each load was strapped onto the right knee attachment of the dynamometer and was dropped through a 100 degrees arc of motion five times at each preset speed using the soft and hard cushion settings. MAIN OUTCOME MEASURES Peak velocity, peak torque, time to peak velocity, time to peak torque. RESULTS Peak velocity was significantly influenced by the cushion setting, the weight dropped, and the preset speed. Maximal peak velocity achieved was 400 degrees/sec. Peak torque was influenced significantly by the cushion setting, the load, and the preset speed. Maximal peak torque measured was 34.99 kg-m. CONCLUSION The rotating shaft of Biodex II dynamometer moved at a slower speed through the entire arc of motion at the soft cushion setting and often failed to achieve a constant, preset speed. Peak torque measured using the soft cushion setting was more variable and therefore questionable.

Demonstrating the Stretch Reflex: A Mechanical Model

If you wish to explain the concept of stretch reflexes to your students, it may be helpful to present the information using a mechanical model. The mechanical model has the advantage of providing a dynamic multisensory experience using movement, light and sound. The model, which can be an adjunct to less dynamic textbook sources, enables instructors to teach an abstract phenomenon in a concrete manner. The choice of jargon used during the demonstration will depend on the age and sophistication level of your audience (technical jargon is in parentheses).