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Movement biomechanics of sit-to-walk across the lifespan
Miller, Michael Francis
Miller, Michael Francis
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2023
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2025-06-24
Abstract
Effective balance control is important for biomechanical performance during transitional movements like sit-to-walk (STW). Injuries, neuromuscular deficits, and aging affect this performance, resulting in compensations like adjusting foot position or using arm supports when rising. These compensations can affect ground reaction forces (GRFs), body center of mass (COM) displacements, and lower limb muscle recruitment, crucial variables for STW balance control. However, a systematic analysis of how foot position, arm support, and aging effects STW biomechanics does not exist. Therefore, this study aimed to determine how asymmetric foot positions and arm supported push-off strategies affect movement to provide insight into balance control when rising and walking movements are merged. A literature review was completed of clinical balance assessments, STW compensation strategies, and the physical capacities that drive movement behavior was completed. Fifteen healthy (18-35 years) and 15 healthy older (50-79 years) adults performed STW from four initial foot positions and two arm positions while motion capture, GRFs, and muscle electromyography were collected. Older adults had greater peak knee extensor, plantarflexor, and gluteus medius (GMED) muscle activity compared to younger adults, consistent with a proximal shift in muscle recruitment and greater ankle co-contraction. Older adults generated the greatest mediolateral GRFs during first step contact, whereas younger adults did so while rising. Thus, initial foot position and age affect whole-body COM motion and GRFs after rising. Rising with arm support from the knees reduced peak lumbar paraspinal (LP), vastus lateralis, and rectus femoris muscle activity. A posteriorly offset foot position reduced peak activity in LP and GMED for both limbs and lowered knee extensor activity on the stance limb, but required greater peak knee extensor and plantarflexor activity on the stepping limb. We recommend that older adults rise with arm support to reduce LP and knee extensor muscle activity. Adopting a wide initial foot position may not be advantageous due to greater demands on plantarflexor muscles for lateral stability. A posterior offset foot position can lower stance limb LP and GMED, but the muscular strength and joint health of the stepping limb should be considered.
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