The Influence of Movement Velocity Biofeedback on Muscle Activation and Self Perception in Older Adults With Sarcopenia

BEHAVIORAL

Experimental: External Focus

Participants will perform a short, standardized warm-up (1 set of 10 repetitions of 20% of the participant's estimated 1-repetition maximum). Following the warm-up, participants will perform 30 repetitions using 50% of their estimated 1-repetition maximum on a leg press machine. Participants will receive visual feedback from a linear position transducer for each repetition, indicating the speed of the last repetition/movement.

BEHAVIORAL

Other: Internal Focus

Arm Description: Participants will perform a short, standardized warm-up (1 set of 10 repetitions of 20% of the participant's estimated 1RM). Following the warm-up, participants will perform 30 repetitions using 50% of their estimated 1-repetition maximum on a leg press machine. Participants will NOT receive visual feedback for each repetition. This is the control condition.

Percent Velocity Loss

Time frame: Week 1 and Week 2 Timepoints

The linear position transducer is a spring-powered retractable apparatus that attaches to the leg press on one end and to the machine near the participant's hip joint. Velocity data from a linear position transducer will be collected following each repetition. Percent velocity loss (%VL) measures the reduction in the movement speed from the initial repetition to the final repetition. The %VL will quantify the level of fatigue and performance decline that occurs throughout the repetitions of leg press. This would suggest that a higher %VL would indicate a greater degree of fatigue, while a lower %VL loss would indicate a better ability to maintain movement velocity across the repetitions.

Muscle Activation

Time frame: Baseline, Week 1, and Week 2 Timepoints

To examine muscle activation, surface electromyographic (sEMG) signals will be collected in millivolts (mV) during each repetition using wireless sEMG sensors from the right vastus lateralis. A higher number of millivolts is associated with greater muscular activation. All sEMG signals will use a commercially available signal acquisition system. To optimize signal quality, the skin will be prepared, and the surface electrodes will be secured to the skin with skin-sensor adhesive in a standardized position directly above the muscle in line with the muscle fiber pennation in a bipolar fashion. An electrogoniometer will be placed across the right knee's joint space. The electrogoniometer will be calibrated to 90° flexion and 180° full extension of the knee joint.

Motivation

Time frame: Week 1 and Week 2 Timepoints

The Dundee Stress State Questionnaire (DDSQ) has been used to determine task stress and performance impact of stress on task completion. Our proposal focuses on the motivation construct (15 item questionnaire, \~5 minutes to complete) of the DDSQ which has been shown to be reliable and scored on a 4-point Likert scale (Extremely = 4 Very much = 3 Somewhat = 2 A little bit = 1 Not at all = 0). The maximum score possible is 60 points and minimum score possible is 0 points. Higher scores indicate higher motivation. Note that certain items are reverse coded when scoring. Motivation will be assessed before sessions to determine baseline motivation to complete the resistance training protocol and 10 minutes after the resistance training protocol to determine if the visual movement velocity biofeedback improves motivation throughout the resistance training protocol.

Perceived Workload

Time frame: Week 1 and Week 2 Timepoints

Perceived workload will be assessed using the NASA task index (NASA-TLX). This questionnaire assesses six separate indices that examine the mental demand, physical demand, temporal demand, performance, effort, and frustration level following the completion of the resistance training protocol. Adjusted scores range from 0-500 with higher scores indicate greater demand, failure, higher effort, or higher frustration. The NASA-TLX will provide valuable information about how visual movement velocity biofeedback may change the perceived workload compared to the non-biofeedback condition.

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