Exercise responses in aged rats selected for High versus Low training response

Abstract

Exercise training improves aerobic capacity, but there are a number of gaps in our understanding of the exercise training response: 1) There is a wide variability in the response to training among individuals (both human subjects and rodents), but little is known about the mechanisms underlying this variability in training response. 2) It is unclear to what extent aging affects the ability to adapt to endurance training. To address these questions, we used a contrasting animal model system in which rats were artificially selected for 19 generations into High Response Trainers (HRT) versus Low Response Trainers (LRT), based on their response to aerobic treadmill training. Exercise capacity (as measured by time to exhaustion, EX‐TIME) and VO2max were measured in 22 month old rats and then animals were divided into Sedentary (SED) vs. Exercise (EX) groups. EX animals were trained 5 days a week for 3 months, with speed and duration gradually increased to the point that animals were running at 14 m/min for 45 min. At the end of the 3‐month training period, exercise capacity and VO2max were again measured in all animals. Mean EX‐TIME and VO2max values significantly (p <0.05) declined in SED animals from Pre‐training (PRE) to Post‐training (POST). EX‐ TIME declined by 35% in POST compared to PRE, while VO2max declined by 26% in POST vs. PRE. In the EX animals there was no significant difference in PRE vs. POST EX‐TIME or VO2max mean values in the LRT group, while in the HRT group, there were significant (p <0.05) increases in EX‐TIME (POST values 147%) of PRE) and VO2max (POST values 131% of PRE). To determine the mechanism of this variability in exercise training response in old animals, we correlated individual animal's improvement in EX‐TIME to measures of their cardiac function using echocardiography and measures of expression of genes related to mitochondrial biogenesis in skeletal muscle. Improvements in EX‐TIME were well correlated with improvements in VO2max. While EX training significantly (p <0.05) improved mean Fractional Shortening (FS%) and Ejection Fraction (EF%) in HRT compared to SED, ( EF% increased by 19% compared to SED; FS% increased by 31%), in individual animals these values did not correlate with improvements in EX‐TIME. However, increases in expression of a number of genes related to mitochondrial biogenesis and PGC‐1alpha signaling were well correlated with improvements in EX‐TIME. These results show that 1) aging animals retain the ability to respond to endurance training with improvements in VO2max and exercise capacity, but a differential to respond between HRT and LRT animals remain, and 2) changes in expression of genes related to mitochondrial biogenesis appear to underlie individual variation in the response to exercise training.Support or Funding InformationSupported by NIH AG 030423