Clinical Measures of Physical Fitness Predict Insulin Resistance in People at Risk for Diabetes

Background and Purpose. Physical inactivity has bee well documented as a risk factor for type 2 diabetes. Previous studies measured the level of physical activity either with questionnaires or with direct measurements of maximum oxygen uptake. However, questionnaires are patient-report measures, and methods for obtaining direct maximum oxygen uptake measurements often are not available clinically. The purpose of this study was to investigate whether clinical measurement of health-related physical fitness with a simple test battery can predict insulin resistance, a precursor of type 2 diabetes, in people at risk for diabetes. Subjects and Methods. A total of 151 volunteers with at least one diabetes risk factor (overweight, hypertension, dyslipidemia, family history, impaired glucose tolerance. gestational diabetes, or delivering a baby weighing more than 4.0 kg) were recruited. Insulin resistance (as determined with the homeostasis model assessment of insulin resistance [HOMA-IR]), physical fitness (including body composition, as determined with the body mass index and waist circumference), muscle strength (handgrip strength [force-generating capacity]), muscle endurance (sit-up test), flexibility (sit-and-reach test), and cardiorespiratory endurance (step test) were measured; and a physical activity questionnaire was administered. Backward regression analysis was used to build the prediction models for insulin resistance from components of physical fitness and physical activity. Results. Body mass index, muscle strength, and cardiorespiratory fitness predicted HOMA-IR in men (adjusted R-2=.264). In women, age, waist circumference, and cardiorespiratory fitness were the predictors of HOMA-IR (adjusted R-2=.438). Discussion and Conclusion. Clinical measures of physical fitness can predict insulin resistance in people at risk for diabetes. The findings support the validity of clinical measures of physical fitness for predicting insulin resistance in people at risk for diabetes.