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Age-Related Differences in Muscle Power during Single-Step Balance Recovery

Michael L. Madigan

The purpose of this study was to investigate agerelated differences in muscle power during a surrogate task of trip recovery. Participants included 10 healthy young men (19–23 years old) and 10 healthy older men (65–83). The task involved releasing participants from a forward-leaning posture. After release, participants attempted to recover their balance using a single step of the right foot. Muscle power at the hip, knee, and ankle of the stepping limb were determined from the product of joint angular velocity and joint torque. Muscle powers during balance recovery followed a relatively consistent pattern in both young and older men, and showed effects of both lean and age. Interestingly, the effects of age did not always involve smaller peak power values in the older men as expected from the well-documented loss of muscle power with aging. Older men exhibited smaller peak muscle power at the knee and larger peak muscle power at the ankle and hip compared to young men. The increases in muscle power at the ankle and hip may result from a neuromuscular adaptation aimed at improving balance recovery ability by compensating for the age-related loss of muscle function.

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Effects of Age-Related Differences in Femoral Loading and Bone Mineral Density on Strains in the Proximal Femur During Controlled Walking

Dennis E. Anderson and Michael L. Madigan

Maintenance of healthy bone mineral density (BMD) is important for preventing fractures in older adults. Strains experienced by bone in vivo stimulate remodeling processes, which can increase or decrease BMD. However, there has been little study of age differences in bone strains. This study examined the relative contributions of age-related differences in femoral loading and BMD to age-related differences in femoral strains during walking using gait analysis, static optimization, and finite element modeling. Strains in older adult models were similar or larger than in young adult models. Reduced BMD increased strains in a fairly uniform manner, whereas older adult loading increased strains in early stance but decreased strains in late stance. Peak ground reaction forces, hip joint contact forces, and hip flexor forces were lower in older adults in late stance phase, and this helped older adults maintain strains similar to those of young adults despite lower BMD. Because walking likely represents a “baseline” level of stimulus for bone remodeling processes, increased strains during walking in older adults might indicate the extent of age-related impairment in bone remodeling processes. Such a measure might be clinically useful if it could be accurately determined with age-appropriate patient-specific loading, geometry, and BMD.

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Expanding Our Scope to Include Biomechanics Education and Outreach

Kimberly Bigelow and Michael L. Madigan

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Age Differences in the Required Coefficient of Friction During Level Walking Do Not Exist When Experimentally-Controlling Speed and Step Length

Dennis E. Anderson, Christopher T. Franck, and Michael L. Madigan

The effects of gait speed and step length on the required coefficient of friction (COF) confound the investigation of age-related differences in required COF. The goals of this study were to investigate whether age differences in required COF during self-selected gait persist when experimentally-controlling speed and step length, and to determine the independent effects of speed and step length on required COF. Ten young and 10 older healthy adults performed gait trials under five gait conditions: self-selected, slow and fast speeds without controlling step length, and slow and fast speeds while controlling step length. During self-selected gait, older adults walked with shorter step lengths and exhibited a lower required COF. Older adults also exhibited a lower required COF when walking at a controlled speed without controlling step length. When both age groups walked with the same speed and step length, no age difference in required COF was found. Thus, speed and step length can have a large influence on studies investigating age-related differences in required COF. It was also found that speed and step length have independent and opposite effects on required COF, with step length having a strong positive effect on required COF, and speed having a weaker negative effect.

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Two Novel Slip Training Methods Improve the Likelihood of Recovering Balance After a Laboratory-Induced Slip

Leigh J. Allin, Maury A. Nussbaum, and Michael L. Madigan

Task-specific balance training is an approach to fall prevention that has the potential to reduce the number of slip-induced falls. However, a limitation of current task-specific training methods is that they require nontrivial financial and/or equipment resources. This pilot study evaluated the efficacy of 2 low-cost, low-tech methods for slip-recovery training in improving balance recovery ability. The 2 methods were as follows: (1) repeated unexpected slip training (UST), which involved repeated unexpected slips while walking (similar to current methods of task-specific slip-recovery training) and (2) volitional slip-recovery training (VST), which involved practicing a slip recovery response after volitionally stepping to induce a slip-like perturbation. A total of 36 young adults completed 1 training session (UST, VST, or control), followed by 1 unexpected, laboratory-induced slip while walking on the following day. Compared with controls, UST and VST resulted in a higher proportion of successful balance recoveries from the laboratory-induced slips. UST improved both proactive control and the reactive stepping response after slipping, whereas VST improved the ability to arrest the motion of the slipping foot. Based on these preliminary results, UST and VST may provide practical, cost-effective methods for slip-recovery training.