Relationships between Maximal and Rapid Torque Characteristics and Chair Rise Power in Very Old Adults

Abstract

Isometric assessments of leg extensor and flexor strength are commonly used to evaluate muscle function in very old adults. It has been hypothesized that maximal and rapid torque characteristics of the leg extensors and flexors may be important predictors of functional performances for movement activities such as walking and stair climbing. However, limited data exist regarding how these parameters associate with muscle power during a chair-rise task. PURPOSE: To examine the relationships between chair-rise power and maximal and rapid isometric torque characteristics of the leg extensors and flexors in very old adults. METHODS: Ten very old adults (mean±SD: age=88±6 years) performed 2 chair rises followed by 2 randomly-ordered isometric maximal voluntary contractions (MVCs) of the leg extensors and flexors. Estimated peak power output (Pmax) was measured during the chair rises using a linear velocity transducer. For each MVC, participants sat in an upright position with the ankle-joint immobilized using a custom-built stabilizing apparatus. All MVCs were performed on the right leg at a knee joint of 90° below the horizontal plane, while restraining straps were placed over the trunk, waist, and thigh. Participants were instructed during each MVC to push or pull “as hard and fast as possible” against a load cell for 3-4 seconds. Isometric peak torque (PT; Nm) was determined as the highest mean 500 ms epoch during the entire 3-4 second MVC plateau. Peak rate of torque development (RTD; Nm·s-1) was quantified from the first derivative of the absolute torque-time curve during its initial ascent. RESULTS: Significant positive relationships were observed between Pmax and RTD for the leg extensors (r=0.681, P=0.030) and flexors (r=0.634, P=0.049); however, no relationships were observed for either muscle group between Pmax and PT (r=0.033-0.262, P=0.465-0.927). CONCLUSION: The present findings of significant relationships between Pmax and RTD of the leg extensors and flexors suggest that explosive strength capacities of the lower extremity musculature may play an important role in chair-rise performances in very old adults. These findings highlight the need for training programs aimed to increase leg extensor and flexor explosive strength for the maintenance and/or improvement of locomotor function in the elderly.