Muscle Characteristics and Substrate Energetics in Lifelong Endurance Athletes

Abstract

Purpose The goal of this study was to explore the effect of lifelong aerobic exercise (i.e. chronic training) on skeletal muscle substrate stores (intramyocellular triglyceride [IMTG] and glycogen), skeletal muscle phenotypes, and oxidative capacity (ox), in older endurance-trained master athletes (OA) compared to non-competitive recreational younger (YA) athletes matched by frequency and mode of training. Methods Thirteen OA (64.8±4.9 yo) exercising ≥ 5 times/week were compared to 14 YA (27.8±4.9 yo) males and females. IMTG, glycogen, fiber types, succinate dehydrogenase (SDH) and capillarization were measured by immunohistochemistry in vastus lateralis biopsies. Fat-ox and carbohydrate (CHO)-ox were measured by indirect calorimetry before and after an insulin clamp and during a cycle ergometer graded maximal test. Results V̇O2peak was lower in OA than YA. OA had greater IMTG in all fiber types and lower glycogen stores than YA. This was reflected in greater proportion of type I and less type II fibers in OA. Type I fibers were similar in size, while type II fibers were smaller in OA compared to YA. Both groups had similar SDH content. Numbers of capillaries per fiber were reduced in OA but with a higher number of capillaries per area. Metabolic flexibility and insulin sensitivity were similar in both groups. Exercise metabolic efficiency was higher in OA. At moderate exercise intensities, CHO-ox was lower in OA but with similar Fatox. Conclusion Lifelong exercise is associated with higher IMTG content in all muscle fibers and higher metabolic efficiency during exercise that are not explained by differences in muscle fibers types and other muscle characteristics when comparing older to younger athletes matched by exercise mode and frequency.

Effects of Exercise and Aging on Skeletal Muscle

“…Chronic exercise in older men and women maintains high insulin sensitivity (Amati et al 2009;Amati et al 2012) similar to that of young endurance-trained athletes (Dube et al 2016). Together, these findings strongly support the idea that age per se is not the cause of skeletal muscle metabolic impairments, and that chronic exercise is a primary determinant of insulin sensitivity.…”

Muscle morphology and performance in master athletes: A systematic review and meta-analyses

“…A total of 12 studies (Carrick-Ranson et al, 2014a;DubÉ et al, 2016;Hawkins et al, 2001;Hayes et al, 2015;Marcell et al, 2003;Marcell et al, 2014;Pollock et al, 2015;Proctor and Joyner, 1997;Sanada et al, 2009;Tarpenning et al, 2004b;Trappe et al, 2013; Yataco et al,…”

“…Only three studies (DubÉ et al, 2016;Schmidt et al, 2015;Yataco et al, 1997) reported measures of whole-body fat mass (FM) measured using DXA or hydrostatic weighing. Three study groups included master endurance athletes (14.1 ± 3.6 kg FM, n=91), 2 study groups included older untrained individuals (20.1 ± 6.3 kg FM, n=65) and 1 study group included young endurance trained individuals (12.0 ± 4.2 kg FM, n=14).…”

“…A meta-analysis was conducted for body fat % for studies that made direct comparisons with master endurance athletes ( Figure 2); this allowed for the greatest number of within-study comparisons to be incorporated into the statistical analysis. Twenty-nine studies (Aagaard et al, 2007;Arbab-Zadeh et al, 2004;Ari et al, 2004;Bjork et al, 2012;Buford et al, 2010;Buyukyazi, 2004;Carrick-Ranson et al, 2014b;Cristea et al, 2008;DubÉ et al, 2016;Hawkins et al, 2001;Hayes et al, 2015;Katzel et al, 1998;Korhonen et al, 2006;Korhonen et al, 2012;Marcell et al, 2003;Marcell et al, 2014;Matelot et al, 2016;Mortensen et al, 2012;Nyberg et al, 2012;Ojanen et al, 2007;Pollock et al, 2015;Proctor and Joyner, 1997;Sallinen et al, 2008;Sanada et al, 2009;Schmidt et al, 2015;Tarpenning et al, 2004a;Trappe et al, 2013;Witkowski et al, 2010;Yataco et al, 1997) reported data for body fat percentage measured using bioelectrical impedance, DXA, hydrostatic weighing or multiple-…”

Master Athletes Are Extending the Limits of Human Endurance

“…For example, Wroblewski et al (2011) showed that despite an increase in total body fat percentage with age, mid-thigh muscle area, quadriceps area, and specific strength did not decline significantly with age in master athletes. Dubé et al (2016) recently showed that lifelong exercise was associated with higher intramyocellular triglyceride and glycogen content in all muscle fibers and higher metabolic efficiency during exercise. From a neuromuscular viewpoint, Power et al (2010) also showed master runners preserved the number of functioning motor units in the tibialis anterior well into the seventh decade of life providing evidence that chronic activity has beneficial effects not only on the muscle fibers but also on the motoneuron.…”