Resting Metabolic Rate, (RMR) accounts for 60-75% of daily caloric expenditure. The greater the individual activity level, the lower the percentage of caloric expenditure expressed in RMR. Such knowledge welcomes study into the effects of exercise on RMR.
Looking at the Numbers
RMR is 60-75% of daily energy output. The thermal effect of feeding, (digestion) provides an additional 5-10%, and the energy expended in physical activity accounts for between 20% and 30% of daily energy output. (McCarger 1996)
The major determinants of RMR include such factors as body surface area, body composition, age, gender, thyroid hormones, genetics, body temperature, and, in women, the phase of the menstrual cycle. Most factors, as you can see, are outside of individual control, however voluntary behaviors, such as manipulating diet and exercise can influence RMR.
The relationship between diet, exercise and metabolism is not a simple one. In to understand the relationship, it is important to measure differences in individuals RMR, as well as Fat Free Mass (MFF) VO2 Max, and Strength.
Many studies have shown that the effects of certain types of exercise outweigh others, based upon their adaptive effect on Lean Tissue, or Fat Free Mass (MFF).
Exercise programs are generally designed to contain three elements: Cardiovascular-Respiratory training (CVR), Resistance or Strength training, (RT) and Flexibility (FT). Flexibility exercises, while important to overall health and the performance of further types of exercise, produces no direct effect on RMR, and little, if any, conclusive studies have been made in this area.
Multiple studies in CVR training and RT programs have been performed to conclude both the direct and indirect effects on RMR, and while the results are varied (depending upon methodologies) there is consistency in certain areas.
Wilmore, et.al, in a 1998 study measured alterations in RMR as a consequence of prolonged endurance (CVR) training. Subjects, in post exercise measurements (24 and 72 hours) showed RMR to be unchanged, even when data was adjusted to account for the confounding effects of age, sex body composition and VO2 max. Wilmore concluded that even following 20 weeks of endurance (CVR) training that no direct effect could be found on RMR, even in the presence of significant changes of VO2 Max and small changes in Body Composition.
Westerterp, et al, provide supportive data through a 1994 study that measure RMR following a prolonged 90 weeks of endurance (CVR based) training. The result- RMR, (or Sleeping Metabolic Rate, as used in this study) was not effected by this training.
Shinkai, et al, in 1994 performed a similar study, interjecting dietary restriction, on mildly obese, middle-aged women. His conclusion- that endurance (CVR) exercise augmented the metabolic activity of lean tissue, providing an indirect effect on RMR and body composition.
These studies have reached similar conclusion. Cardiovascular-Respiratory training, also termed endurance training – produces no direct effect on Resting Metabolic Rate.
When individuals in studies showed RMR variance, it has generally occurred where MFF has also changed.
Smith, et al, in 1997, following acknowledgement that research on the effect of CVR training on RMR was inconclusive, performed a further study incorporating “Aerobic Power”. This study, yet again showing no direct CVR effect on RMR, did yield a result when comparing the observing, and not discounting, mild changes in MFF. It also found that VO2 max has little correlation to these changes.
The core consideration, then must be if our desired outcome is to effect RMR through exercise, we should select activities that produce changes in MFF. The most significant of these, is Resistance Training (RT) due to the effects on skeletal muscle.
Studies producing exercise adaptive effects on RMR show change, also to the Fat Free Mass (MFF). A large portion of human MFF is skeletal muscle tissue.
In a 1995 Study, Bulluogh et al, found that the exercise intensity and frequency influenced MFF and RMR. Longitudinal program studies have shown that by increasing or maintaining MFF whilst restricting calories, has a significant effect on decreasing body fat through increasing RMR. (Karch, 1994)
Resistance and Strength training exercises, it may be concluded, have a direct effect on MFF, therefore, also an effect on RMR. Exercise, we can therefore state, can have an indirect effect on RMR. Studies, however, are inconclusive to the absolute significance , and degree of effective change.
In all exercise programs, professionals must balance CVR, RT and FT to meet a desired client goal or outcome. Many individuals use exercise as a means of altering body composition. The “Diet and Exercise” equation has not changed. The diet “merry-go –round ” (decreasing calories, decreasing RMR) spirals the individual toward ultimate failure.
As previously indicated, RMR accounts for 60-75% of daily caloric expenditure. Programming exercise to increase caloric expenditure at rest may be one goal in the weight management equation. Total caloric expenditure on a daily basis, however, also encompasses all daily activity. CVR programming can play a large part in an individuals daily caloric expenditure. Bouts of 30 minutes or more of CVR activity often yield caloric expenditures of up to 300 calories, depending upon the individuals total weight and exercise intensity. CVR training, for this reason, plays an important part in the weight management equation.
Resistance training has a caloric expenditure effect whilst being performed, and it can also have a dramatic effect on lean tissue growth.
Resistance Training Outcomes
Not all individuals express the identical outcomes from RT programs. Smith, et al,(1999) found that long term exercisers produced mild change in RMR through exercise as opposed to non exercisers.
Gornall, in 1996 found that a 4-week program of RT with caloric restrictions did not prevent or reduce the decline in MFF and RMR.
Two important elements are uncovered here:
1. That Resistance Training, unless coupled with an appropriate, caloric based diet for the maintenance and growth of lean tissue, cannot effect RMR, and
2. That Resistance Training adaptations vary per the individuals current training state, and the time required (>4 weeks) to yield lean tissue adaptation.
Programming exercise to assist in improving weight loss, through effecting RMR, is therefore a challenging equation. Supporting factors, such as the individual’s current state of fitness, diet (caloric quality and quantity), gender and age, and “trainability” (neuromuscular ability to exercise) all must be considered. Based upon the correlation effects of lean tissue change and RMR change, however, we may make the assumption that Strength Training is a better exercise choice.
Resistance by Design
All factors considered, the greater the chance for lean tissue adaptation, the greater the opportunity to affect RMR through exercise. Training that produces lean tissue gains is generally
a.) Resistance applied to major muscle groups, such as the quadriceps group, the gluteals, the pectorals, latissimus and deltoid group.
b.) Resistance applied for short durations of high (80% or more of 1RM) intensity
c.) Resistance applied to these muscles a minimum of twice per-week to yield adaptation (hypertrophy), and
d.) Ongoing training that maintains a desired level of hypertrophy to avoid muscular atrophy.
Multiple factors are required in the production of any exercise regimen. If increasing RMR is the desired outcome, specific exercise “side-effects”, such as reprogramming the neuromuscular system, muscular balance to reduce the chance of injury and the effect on an individuals overall health (cardiovascular system) must also be considered if the professional is to employ an engaging, qualitatively based program. Stressing this importance to the client, and knowing the pitfalls of excessive or aggressive resistance programs is a core professional responsibility.
Exercise can effect RMR. The choice of exercise is important, if such changes are to occur. Multiple studies show the non-effect of endurance and CVR training, and correlate the effects of MFF with changing RMR.
Resistance training yields change in MFF. Therefore, the indirect ability of Resistance training to effect Resting Metabolic Rate is known. When choosing to program exercise for RMR change, resistance training is the “best choice”. CVR training, as a second consideration, may provide a stimulus to augment metabolic Rate in the adapted muscle cells.
When exercise programming for a single goal of weight management, however, emphasis on effecting TOTAL caloric expenditure is a key consideration. As we can see through research, RT will effect RMR through by increasing lean tissue. Resistance training exercises, while being performed, also require caloric expenditure, as does CVR exercise. If exercise is a tool for weight management, both CVR, and RT, coupled with Flexibility exercises will certainly produce the best overall effect.
Studies are still inconclusive in the amount and significance of change to RMR through resistance training. Further studies, both short and long term, across gender and age, factoring trained and untrained individuals and their unique trainability, is required.
The diet merry-go-round produces negative effects and also produces potential health dangers. Many new dieters seek caloric restriction and generally select activities that are CVR or endurance based. The outcome for many millions of Americans following this pattern is ultimately, failure.
Our collective knowledge and new access to measurement devices to monitor the dynamic nature of RMR, and therefore program accurate exercise and caloric behavior modifications is one of the core answers to a healthier population.