Skeletal Muscle Oxidation During an Incremental Exercise Test in Younger and Middle-aged Individuals

Abstract

Previous research has suggested that age-related decline in mitochondrial enzymes consequently results in reduction of skeletal muscle oxidative function. Limited research exists investigating effects of healthy aging on these observed changes, especially with middle-aged individuals. PURPOSE: The purpose of this study was to investigate the effects of healthy aging on changes in tissue oxygenation in skeletal muscle (SmO2) during a self-paced VO2max (SPV) test in younger and middle-aged subjects. METHODS: This study included seven younger (ages 18-35 years, 4 males, BMI 28.1±3.4 kg/m2) and nine middle-aged (ages 40-55 years, one male, BMI 25.1±3.8 kg/m2) healthy, recreationally active individuals. Subjects visited the lab once to complete the SPV test on a Wattbike cycle ergometer. The Moxy sensor, which uses near-infrared spectroscopy, was used to estimate SmO2. Four Moxy sensors were used and were placed on the right and left quadriceps (vastus lateralis), and right and left gastrocnemius muscles. The SPV test was exactly ten minutes in length, with five 2-minute stages. Each stage was perceptually regulated using the 6-20 rating of perceived exertion (RPE) scale: 11, 13, 15, 17, and 20 (in that order). Repeated-measures ANOVAs were used to compare SmO2 between anatomical sites and stages of the SPV. Age group was used as a between-subjects factor. RESULTS: Measured VO2max was 48.33±7.56 ml/kg/min for the younger and 38.10±7.45 ml/kg/min for the middle-aged subjects. For SmO2, there was no main effect of anatomical site (p=0.170) and no differences between age groups (p=0.906). A main effect was present for SPV stages (p<0.001); values remained steady until the last two stages, where they decreased in both groups (younger: 71.0±3.1, 69.5±3.5, 67.9±3.7, 63.6±4.5, 58.3±5.9 percent; middle-aged 69.4±2.8, 70.4±3.1, 70.4±3.3, 65.4±4.0, 56.1±5.3 percent). CONCLUSION: Since no age-related differences were found in SmO2 during the exercise test, healthy aging (i.e. regular aerobic exercise) can be seen as an effective intervention for maintenance skeletal muscle blood flow and a profound influence for sustaining quantity and quality of mitochondria function. Future research should determine whether the same findings occur with healthy, active elderly subjects.