Effects of Overload Eccentric and Concentric Resistance Training on the Cost of Walking, Muscle-tendon and Jumping Performance in Healthy Older Individuals

Overview

Normal aging leads to a decline in neuromuscular and mobility functions, including a 60% reduction in maximal voluntary force production, a 25% decrease in muscle volume and quality (sarcopenia), and reduced tendon stiffness by age 70. These changes impair walking speed, balance, and increase the metabolic cost of walking by \~20% in older adults compared to younger individuals. While walking training can reduce metabolic costs, no interventions have successfully addressed the 20% age-related difference. Resistance training, particularly eccentric (muscle-lengthening) training, shows promise for improving muscle strength and mass, but its effects on functional, cognitive abilities, and walking economy in older adults remain unexplored.

Normal aging is characterized by a decline in neuromuscular and mobility functions. By the age of 70, maximal voluntary force production decreases by approximately 60%, accompanied by a \~25% reduction in muscle volume and quality, leading to sarcopenia. Alongside changes in muscle protein content, composition, and mitochondrial biochemistry, aging also affects tendon properties. While healthy aging does not significantly alter tendon size, it reduces tendon stiffness, which can delay force transmission. These changes in muscle-tendon function contribute to slower walking speeds and impaired static and dynamic balance. One of the most significant functional changes with aging is the increased metabolic cost of walking. Older individuals require \~20% more metabolic energy to walk the same distance as younger adults, yet the underlying reasons remain unclear. While walking training has been shown to reduce metabolic costs in older adults, no studies have attempted to reduce this 20% age-related difference using alternative interventions. Resistance training induces adaptations in muscle-tendon function by requiring participants to overcome external loads. Traditional resistance training combines concentric (muscle shortening) and eccentric (muscle lengthening) contractions, but eccentric training has received increasing attention due to its superior benefits in muscle strength and mass improvement. However, no studies have examined how resistance training, particularly with an eccentric focus, impacts functional and cognitive abilities or walking economy in older adults. Objectives: This study aims to: 1. Investigate the effects of resistance training, particularly eccentric-focused training, on muscle-tendon function and walking economy in older adults. 2. Examine whether these changes translate into improved neuromuscular and cognitive functions. 3. Determine if improved tendon stiffness leads to more efficient force transmission, reducing walking energy expenditure.