Determination of structural and functional thigh muscle properties in a healthy older population using MRI and isokinetic dynamometry

Background: No consistent findings have been reported regarding the relationship between aging muscle size and strength. This may be due to the use of an inaccurate method of muscle quantification, anatomical cross-sectional area, and a limited study of muscle group and contraction type. There is little normative data on thigh muscle size and strength, or the nature of relationships among muscle groups of the thigh in a healthy older population. Purpose: 1) To determine the relationship between muscle volume (MV) of the knee flexors, knee extensors, and hip abductors, and their associated muscle strength and fatigue. 2) To investigate the reliability and validity of stereology to determine MV, and to establish the reliability of a protocol to measure hamstring muscle fatigue. 3) To investigate thigh circumference, and determine whether or not it is representative of MV and/or strength. 4) To establish normative strength ratios for this population. Subjects: Healthy older males and females, 51-80 years old. Methods: MV was calculated from MRl’s of the subject’s legs, using stereology. lsokinetic and isometric strength was measured on the Kin-Com Dynamometer, and muscle fatigue was measured using EMG during an 80% maximum voluntary contraction (MVC). Thigh circumference was determined using a Lufkin steel tape measure. Results: Average MV was 1529.57 ± 500.54 cm³ for the quadriceps, 776.46 ± 231.65 cm³ for the adductors, and 613.59 ± 159.73 cm³ for the hamstrings. All three muscle groups showed a good to excellent relationship between MV and strength (r=0.76-0.91). Thigh circumference measures at 10 cm had a strong relationship with size (r=0.55-0.72) and strength (r=0.93) of all muscle groups. Isometric strength ratios were 0.41 for hamstring : quadriceps, and 0.37 for adductor : hamstrings, where MV ratios were 0.51 and 1.03 respectively. The hamstring : quadriceps endurance time ratio was 1.74. Conclusions: The reliability of using stereology to measure MV of the thigh muscles was established, showing strong relationships between thigh muscle size and strength. Muscle strength ratios, and the evidence supporting thigh circumference measures at proximal sites on the thigh to represent functional muscle groups, will assist therapists in the treatment of healthy older adults.Medicine, Faculty ofGraduat