I had come across research that excessive aerobic training in the absence of resistance training could result in a decrease in RMR? Is this true?
You pose a very good question that could be a complicated answer. First, there is the defining of "excessive." Does this mean too much as in over training or just a lot as in an advanced aerobic participant? If this means that there is overtraining and /or the subject is eating too little (not enough calories to sustain recovery) than the answer is not very clear. Essentially, if a person is overtrained as a result of high intensity sprint or power type training (anaerobic) they may express an elevated heart rate and thus an increased RMR via over activity of the sympathetic nervous system. Persons overtrained through aerobic (low intensity) means, especially with inadequate caloric consumption, then there can be a decrease in RMR and any further activity in this overtrained state may only perpetuate the problem.
If excessive just means "a lot", then this study may help answer your question:
- Effects of resistance vs. aerobic training combined with an 800 calorie liquid diet on lean body mass and resting metabolic rate, Bryner RW, Ullrich IH, Sauers J, Donley D, Hornsby G, Kolar M, Yeater R., Department of Human Performance and Applied Exercise Science, West Virginia University, Morgantown 26506, USA., J Am Coll Nutr 1999 Apr;18(2):115-21
Utilization of very-low-calorie diets (VLCD) for weight loss results in loss of lean body weight (LBW) and a decrease in resting metabolic rate (RMR). The addition of aerobic exercise does not prevent this. The purpose of this study was to examine the effect of intensive, high volume resistance training combined with a VLCD on these parameters.
Twenty subjects (17 women, three men), mean age 38 years, were randomly assigned to either standard treatment control plus diet (C+D), n = 10, or resistance exercise plus diet (R+D), n = 10. Both groups consumed 800 kcal/day liquid formula diets for 12 weeks. The C+D group exercised 1 hour four times/week by walking, biking or stair climbing. The R+D group performed resistance training 3 days/week at 10 stations increasing from two sets of 8 to 15 repetitions to four sets of 8 to 15 repetitions by 12 weeks. Groups were similar at baseline with respect to weight, body composition, aerobic capacity, and resting metabolic rate. RESULTS: Maximum oxygen consumption (Max VO2) increased significantly (p<0.05) but equally in both groups. Body weight decreased significantly more (p<0.01) in C+D than R+D. The C+D group lost a significant (p<0.05) amount of LBW (51 to 47 kg). No decrease in LBW was observed in R+D. In addition, R+D had an increase (p<0.05) in RMR O2 ml/kg/min (2.6 to 3.1). The 24 hour RMR decreased (p<0.05) in the C+D group. CONCLUSION: The addition of an intensive, high volume resistance training program resulted in preservation of LBW and RMR during weight loss with a VLCD.