11% of the variability in RMR (P<0.0001) in
American Indians from 54 families. Similarly,
Bouchard et al. (1989) found that in twins and
parent–child pairs, heritability explained
approximately 40% of the variability in RMR
after adjusting for age, gender and FFM.
Research now indicates that RMR may fluctu-
ate over the phases of the menstrual cycle, with
RMR values lowest during the follicular phase
and highest during the luteal phase (Solomon
et al. 1982; Bisdee et al. 1989). The difference in
RMR between these two phases is approximately
420–1260 kJ · day–1 (100–300 kcal · day–1). It also
appears that adaptations in energy intake mimic
the changes in RMR. Barr et al. (1995) found that
females consume approximately 1260 kJ · day–1
(300 kcal · day–1) more during the luteal phase of
the menstrual cycle than during the follicular
phase. Thus, the increased energy expenditure,
due to a higher RMR during the luteal phase, is
compensated by an increase in energy intake
during this period. However, if an athlete is
amenorrhoeic, these changes in RMR will not
occur. Data are not available for anovulatory
females who may be menstruating but have
depressed hormonal profiles. Although there
is substantial research to suggest that RMR
changes over the menstrual cycle, not all research
is supportive of these findings. Weststrate (1993)
showed no effect of menstrual cycle on RMR, and
Pierset al. (1995) showed no effect of menstrual
cycle phase on RMR or energy intake.
effect of exercise on rmr
For the athlete participating in an intense train-
ing programme, exercise may affect RMR both
directly and indirectly. First, exercise can directly
increase RMR if it increases FFM (Bogardus et al.
1986). Second, intense exercise training can
temporarily increase resting energy expenditure
above the typical RMR long after the exercise
bout has ended. This short-term increase in
energy expenditure is termed excess postexercise
oxygen consumption (EPOC) and is the amount
of energy expended above the typical RMR. The
extent of EPOC after an exercise bout and the
474 practical issues
effect it has on TDEE appears to depend on
the exercise intensity and/or the duration (Bahr
1992). For example, Bahr et al. (1987) found that
aerobic exercise (70% V.
o2max.) lasting 80 min pro-
duced a 15% increase in EPOC lasting for 12 h
after exercise. Similarly, 2 min of exercise at 108%
V.
o2max., repeated three times, produced a signifi-
cant increase in EPOC for 4 h after exercise (Bahr
et al. 1992). Although most research has exam-
ined the effect of aerobic exercise on EPOC,
Melbyet al. (1993) found a significant increase in
EPOC after 90 min of weightlifting. Oxygen con-
sumption was elevated by 5–10% over baseline
the following morning.
Finally, it appears that energy flux can also
alter RMR. Energy flux is defined as the amount
of energy expended in exercise compared with
the amount of energy consumed each day. An
athlete who is exercising intensely and eating
adequate energy would be in high energy flux,
while an athlete who is exercising intensely, but
restricting energy intake would be in negative
energy flux. Bullough et al. (1995) examined the
effect of energy flux on RMR in trained male
athletes. They measured RMR after 3 days of
high-intensity exercise (90 min of cycling at 75%
V.
o2max., while eating adequate energy) and after
3 days of exercise when energy intake was
reduced (energy intake matching that required
on a no-exercise day). They found that RMR
was significantly higher during high energy than
during negative energy flux. Thus, two athletes
may be doing similar workouts, but have dra-
matically different energy expenditures if one is
restricting energy intake and the other is not.Factors that influence TEF
A number of factors can influence how athletes’
bodies respond metabolically to the food they
consume. Some of these factors are associated
with the physiological characteristics of an indi-
vidual such as genetic background, age, level of
physical fitness, sensitivity to insulin, or level of
body fat. Other factors are associated with the
meal, such as meal size, composition, palatability
and timing.