Abstract The main purpose of this study was to compare three methods of determining relative effort during sit-to-stand (STS). Fourteen young (mean 19.6 ± SD 1.2 years old) and 17 older (61.7 ± 5.5 ...years old) adults completed six STS trials at three speeds: slow, normal, and fast. Sagittal plane joint torques at the hip, knee, and ankle were calculated through inverse dynamics. Isometric and isokinetic maximum voluntary contractions (MVC) for the hip, knee, and ankle were collected and used for model parameters to predict the participant-specific maximum voluntary joint torque. Three different measures of relative effort were determined by normalizing STS joint torques to three different estimates of maximum voluntary torque. Relative effort at the hip, knee, and ankle were higher when accounting for variations in maximum voluntary torque with joint angle and angular velocity (hip = 26.3 ± 13.5%, knee = 78.4 ± 32.2%, ankle = 27.9 ± 14.1%) compared to methods which do not account for these variations (hip = 23.5 ± 11.7%, knee = 51.7 ± 15.0%, ankle = 20.7 ± 10.4%). At higher velocities, the difference in calculating relative effort with respect to isometric MVC or incorporating joint angle and angular velocity became more evident. Estimates of relative effort that account for the variations in maximum voluntary torque with joint angle and angular velocity may provide higher levels of accuracy compared to methods based on measurements of maximal isometric torques.
Approximately one in three adults 65 years and older fall each year and these falls lead to a substantial number of serious injuries and deaths. Numerous interventions have been proposed for ...fall-prevention but the efficacy can vary, and may be due to the general nature of the interventions. Older adults may be able to improve their ability to recover from a postural perturbation through perturbation-based balance training (PBBT), similar to the way other motor skills can be improved through training.
The purpose of the first study was to investigate the effects of age and fall risk on the efficacy of PBBT. Participants (young adults, older adults at low-risk of falling, older adults at high-risk of falling) completed PBBT on a moving platform three times a week for one month. Balance was quantified using the time to stabilization of the COP and normalized to platform displacement (nTTS), where a decrease in nTTS can be interpreted as an improvement in balance. A significant main effect of group revealed high-risk fallers had a significantly higher nTTS than young adults and a significant main effect of session revealed nTTS was significantly lower one week and one month post-training than before training.
The purpose of the second study was to investigate the effect of training amount on the efficacy of PBBT in older adults. Ten healthy older adults completed PBBT either three times a week or five times a week for four weeks. Both training amounts were sufficient for significant improvements in nTTS one week after training. However, training five times a week was necessary for older adults to maintain improvements in nTTS one month post training.
The purpose of the third study was to investigate the need for PBBT after strength training in order to improve balance in older adults. A torque-driven, three-segment, musculoskeletal model and forward dynamic simulations were used to address the hypothesis. Increasing joint strength was beneficial in recovering balance from a postural perturbation only after re-optimization of the torque activation. These results provide support for supplementing strength training fall prevention interventions in older adults with task-related practice.
Ph. D.
Falls are a leading cause of injury and death in older adults. Numerous exercise interventions have been explored for fall prevention with their effectiveness being inconsistent. An alternative ...intervention based on motor learning concepts has potential to help prevent falls. Two separate studies are reported in this thesis. The purpose of the first study was to investigate if older adults exhibit short-term performance adaptation and long-term motor learning with repeated exposures to a simulated trip. While in a safety harness, participants stood on a treadmill that was quickly accelerated to simulate a trip. Improvements in trip recovery performance due to repeated exposures of a simulated trip included arresting the forward rotation of the trunk more quickly, reacting to the perturbation more quickly, and decreasing agonist/antagonist co-contraction. Overall, the results provide evidence for both short-term performance adaptation and motor learning. The purpose of the second study was to investigate if skills obtained from repeated exposure to a simulated trip transfer to recovery from an actual trip. Participants were randomly assigned to either an experimental or control group performing one trip before and after an intervention. The intervention for the experimental group consisted of trip recovery training on a treadmill while the intervention for the control group was walking on a treadmill. Overall, the results suggested beneficial effects of trip recovery training on actual trip recovery. These beneficial effects included decreasing maximum trunk angle, decreasing the time to reach maximum trunk angle, and raising minimum hip height during the initial recovery step.
Master of Science
Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 2009.
Title from electronic submission form. Abstract. Includes bibliographical references.
