Insulin Sensitivity and Motor Performance in Non-Diabetic Older Adults

Abstract

Insulin sensitivity decreases with age, impairing glucose uptake and metabolism in skeletal muscle (Abbatecola et al. 2005), which may contribute to the decline in neuromuscular function seen in older adults (Abbatecola & Paolisso 2008, Schwartz et al. 2004). PURPOSE: To determine the association between insulin sensitivity and motor performance in healthy, non-diabetic older adults. METHODS: Twenty older adults (14 women, 75.1± 6.2 yrs) underwent an intravenous glucose tolerance test (ivGTT) to determine fasting blood glucose and insulin, insulin sensitivity index, glucose sensitivity, and acute insulin response to glucose. Motor performance was characterized with four sets of standardized tests to measure function, muscle strength (maximal voluntary contraction (MVC)), steadiness (60-s isometric dorsiflexion contraction at 5 and 20% MVC force), and muscle endurance (dorsiflexion at 20% MVC force). Force, acceleration, and EMG of the tibialis anterior, gastrocnemius, rectus femoris and vastus lateralis, as well as rating of perceived exertion, mean arterial pressure, and heart rate were measured during the steadiness and fatiguing contractions. RESULTS: Fasting blood glucose (91 ± 8.26 mg/dl) was in the normal range for all subjects. A two-tailed, linear regression analysis showed no significant correlations between any ivGTT outcome and measures of muscle strength, function, or muscle endurance. However, several significant correlations were observed between ivGTT outcomes and measures of steadiness at 5% and 20% MVC. Fasting blood glucose levels were significantly correlated with the standard deviation of force at during steady contractions at 20% MVC (r = 0.493, p = 0.038) and normalized aEMG of vastus lateralis at 5 and 20% MVC (r = -0.581, p = 0.023; r = -0.531, p = 0.028). Glucose sensitivity was associated with aEMG of medial gastrocnemius (r = 0.551, p = 0.33) and agonist-antagonist coactivation ratio between gastrocnemius and tibialis anterior (r = 0.618, p = 0.018) at 20% MVC. A similar trend for coactivation ratio was observed at 5% MVC (r = 0.526, p = 0.053). CONCLUSIONS: Force steadiness and EMG activity of selected leg muscles during isometric contractions with the dorsiflexor muscles were associated with some measures of insulin sensitivity in non-diabetic older adults. NIH 1UL1 RR025780