Chronic Physical Activity and Feelings of
Energy and Fatigue
PATRICK J. O’CONNOR and TIMOTHY W. PUETZ
Department of Exercise Science, University of Georgia, Athens, GA
O’CONNOR, P. J., and T. W. PUETZ. Chronic Physical Activity and Feelings of Energy and Fatigue. Med. Sci. Sports Exerc., Vol.
37, No. 2, pp. 299–305, 2005. This brief review summarizes key epidemiological and experimental evidence concerning relationships
between chronic physical activity and feelings of energy (vigor, vitality) and fatigue. The epidemiological studies show a positive
association between the amount of typical weekly physical activity reported and the frequency with which people report feeling
energetic. The randomized controlled experiments show that 10–20 wk of exercise training is associated with an increase in the
frequency and intensity of feelings of energy among fatigued people with medical conditions. The results of longitudinal studies with
nonfatigued, healthy adults are mixed. Overtraining by athletes is associated with increased intensity of feelings of fatigue. Additional
well-controlled investigations into relationships between physical activity and feelings of energy and fatigue, especially among
sedentary and fatigued individuals, are warranted given the available evidence and the importance of these moods to health, work
productivity, and quality of life. Key Words: DEPRESSION, EXERCISE, INACTIVITY, MOOD, POMS, QUALITY OF LIFE,
SF-36, VIGOR, VITALITY
(lack of vitality or vigor) in part because so many people
experience these feelings. Epidemiological surveys of more
than one million people indicate that nearly one-quarter of
the population feels prolonged and disabling fatigue (30).
Feelings of low energy are among the most common com-
plaints expressed during pregnancy (10). Feelings of low
energy and fatigue are associated with a wide range of major
physical and psychiatric conditions and illnesses including
heart disease, congestive heart failure, stroke, cancer, HIV/
AIDS, obesity, chronic obstructive pulmonary disease, ane-
mias, sleep apnea, multiple sclerosis, rheumatoid arthritis,
chronic fatigue syndrome, fibromyalgia, anxiety, and de-
pression (11,13,14,16,18,20,26,45,46). Feelings of fatigue
and low energy also are common side effects of medicines
used to treat psychiatric conditions as well as a variety of
other medical concerns including cancer (38). In short,
feelings of fatigue and energy are strongly associated with
health and quality of life. A better understanding of energy
and fatigue feelings ultimately could contribute to improve-
xercise scientists and sports medicine practitioners
should be interested in the influence of regular phys-
ical activity on feelings of fatigue and low energy
ments in work productivity, quality of life, and the diagnosis
and treatment of a myriad of fatigue-related health problems.
This review examines relations between chronic physical
activity and feelings of energy and fatigue. Feelings of
energy and fatigue have been conceived in various ways
including as synonyms of alertness-sleepiness (28), moods
(31), symptoms (32), personality traits (23), and dimensions
of cognitive effort (47). The focus here will be on energy
and fatigue conceptualized as moods.
Mood states are subjective, transient feelings that people
report experiencing. The mood of energy can be defined as
positive feelings about the capacity to complete mental or
physical activities. The mood of fatigue can be defined as
negative feelings concerning a reduced capacity to complete
mental or physical activities. Theoretically, these mood
states are associated with, yet distinguishable from, numer-
ous related constructs including muscle fatigue, perception
of effort, the trait of self-motivation, and self-efficacy. For
example, a person with feelings of low energy could con-
comitantly have high self-motivation or high self-efficacy
(e.g., a person who thinks that she could successfully per-
form a specified task).
Moods of energy and fatigue have been operationalized
here using either the vigor and fatigue scales of the Profile
of Mood States (POMS) questionnaire or the vitality scale of
the SF-36 Health Survey because the key epidemiological
and exercise training investigations identified by our liter-
ature search used these measures. Although these instru-
ments are the most frequently used and highly cited mea-
sures of feelings of energy and fatigue, dozens of measures
have been created in the last decade to quantify symptoms
of fatigue and related concerns associated with medical
Address for correspondence: Patrick J. O’Connor, Department of Exercise
Science, University of Georgia, Athens, GA 30602-6554; E-mail:
Submitted for publication May 2004.
Accepted for publication October 2004.
MEDICINE & SCIENCE IN SPORTS & EXERCISE®
Copyright © 2005 by the American College of Sports Medicine
The vitality scale of the SF-36 originally was conceptu-
alized as a measure of well-being (50). However, a case has
been made that the item content and scoring of the vitality
scale combined with the extant literature indicate that it is
more precisely defined as a measure of the prior month
frequency of the bipolar mood of energy-fatigue (36). Bi-
polar refers to conceptualizing the presence of energy and
fatigue as polar opposites of a single mood continuum. This
approach is simpler than conceiving energy and fatigue
moods as two separate psychological constructs (i.e., unipo-
lar). For instance, the unipolar approach allows for the
possibility of a person having simultaneous feelings of en-
ergy and fatigue. Although it is unlikely that strong feelings
of both energy and fatigue would occur regularly, there are
circumstances during which mixed feelings of energy and
fatigue reasonably might coexist (e.g., at the birth of a
The vigor and fatigue scales of the POMS differ from the
SF-36 vitality scale in that they are unipolar and they mea-
sure the intensity of energy and fatigue feelings experienced
at the moment or recalled during a day, week, or month (31).
A large body of convergent psychological, behavioral, and
biological evidence supports the validity of interpreting
POMS vigor and fatigue scores as measures of the intensity
of the moods of energy and fatigue, respectively (31,36).
One biologically oriented example is the observation that
reductions in POMS fatigue scores after treatment for de-
pression were significantly associated with changes in the
metabolism of the frontal cortex as measured by positron
emission tomography (r ? 0.39). Specifically, the improve-
ments in fatigue were associated with decreased ventral
frontal lobe metabolism, especially in the right lobe (7). An
even larger corpus of evidence supports the validity of
interpreting SF-36 vitality scores as a measure of the bipolar
mood of energy fatigue (36).
The primary purpose of this brief review is to summarize
what we consider to be key epidemiological and experimen-
tal evidence regarding the relationship between chronic
physical activity and feelings of energy and fatigue. Liter-
ature was identified by searching the Current Contents,
PsycInfo, Web of Science, and PubMed databases using the
terms fatigue and energy combined either with exercise and
physical activity or with epidemiology, prevalence, or inci-
dence. Papers concerning chronic physical activity and feel-
ings of energy and fatigue were identified and reference lists
of these articles were examined for any additional relevant
sources. This literature search revealed 7 epidemiological
studies, 82 experimental studies with medical patients, and
15 experimental studies with healthy sedentary adults. In-
vestigations that measured feelings of energy or fatigue as a
multidimensional concept in which, for example, scores on
items that assess feelings of fatigue are combined with
scores on items that assess consequences of fatigue (e.g., I
can’t think, I can’t work, etc., . . .) were excluded. This was
done in order to focus this review on studies that examined
feelings of energy and fatigue per se. To keep this review
brief, we subjectively identified key investigations as those
that had research design strengths compared with other
studies of the same type (e.g., larger vs smaller epidemio-
logical studies; randomized, controlled experiments vs
All of the cross-sectional epidemiological investigations
have shown a positive association between physical activity
and feelings of energy. Specifically, as self-reported weekly
physical activity increased, the frequency of energy feelings
reported tended to increase (9,11,27). To illustrate the find-
ings, consider the Women’s Health Australia project (9).
Three national cohorts of women between the ages of 18–23
(N ? 14,502), 45–50 (N ? 13,609), and 70–75 yr (N ?
11,421) were surveyed. Feelings of energy were measured
using the SF-36 vitality scale. A physical activity score was
derived from two questions: one concerned the number of
vigorous exercise bouts of 20 or more minutes in a normal
week, and the other queried the number of “less vigorous”
exercise bouts of 20 or more minutes in a normal week. The
reported weekly exercise bouts were coded (never ? 0, 1?
wk?1? 1, 2–3? wk?1? 2.5, 4–6? wk?1? 5, every
day ? 7, and more than 1? d?1? 10), multiplied by an
intensity factor (vigorous ? 5 or less vigorous ? 3), and
summed. The possible physical activity scores ranged from
0 to 80, and the average (?SD) score for all study partici-
pants was 15 (??13).
A negatively accelerating dose–response relationship was
found between typical weekly physical activity and the
frequency of energy feelings in the Women’s Health Aus-
tralia project. Because the shape of the relationship was
similar for the three age groups, Figure 1 depicts the rela-
tionship for three cohorts combined. As women reported
more weekly physical activity, they also reported more
frequent feelings of energy. Sedentary women reported the
most frequent feelings of low energy and fatigue.
FIGURE 1—The relationship between typical weekly physical activity
and the prior month frequency of energy-fatigue feelings measured by
the SF-36 vitality scale among 39,532 Australian women. The mean
? SD from a representative sample of 1412 adult U.S. women is 58 ?
21 (48); reprinted with permission from Research Quarterly for Exer-
cise and Sport, Vol. 71(3), Copyright 2000 by the American Alliance for
Health, Physical Education, Recreation and Dance, 1900 Association
Drive, Reston, VA 20191.
Official Journal of the American College of Sports Medicinehttp://www.acsm-msse.org
The shape of the curve shown in Figure 1 implies that
fatigued, sedentary individuals who adopt any level of phys-
ical activity would reap the greatest psychological benefit of
increased feelings of energy. Such implications, although
generally consistent with public health recommendations
such as those made in the Surgeon General’s report on
physical activity (48), are best considered in conjunction
with data from experiments. There are a number of alterna-
tive explanations for the data depicted in Figure 1, including
that the relationship could be the result of chronically ill
people being less able to be physically active. This possi-
bility was considered in one report from the U.S. Nurses
Health Study. In this analysis, the strength of relations was
determined between feelings of energy (SF-36 vitality
scores) and physical activity level (estimated MET-hours
per week) as well as nine other variables potentially related
to feelings of energy (i.e., body mass index, smoking status,
alcohol consumption, menopause status, minority status,
and the presence or absence of arthritis, diabetes, hypercho-
lesterolemia, and hypertension). Stepwise regression analy-
ses of data from 56,510 women participants (aged 45–71 yr)
found that physical activity was the strongest predictor of
SF-36 vitality scores (11).
We are aware of only one prospective, epidemiological
investigation addressing relations between changes in phys-
ical activity and changes in feelings of energy. Adult pa-
tients (N ? 1758) enrolled in the longitudinal portion of the
Medical Outcomes Study were tested twice over a 2-yr
period (45). All participants had one or more of the follow-
ing medical conditions: congestive heart failure, depression,
diabetes, hypertension, or a recent myocardial infarction.
After statistically controlling for potential confounders (i.e.,
age, body weight, education, gender, ethnicity, smoking,
drinking, disease condition, comorbidity, poverty, method
of payment, seasonality, and provider type), the total time
spent exercising measured at the baseline time point was a
statistically significant predictor of the frequency of energy
feelings 2-yr later as measured by the vitality scale of the
SF-36. Those who reported a high level of physical activity
at baseline reported more frequent feelings of energy 2 yr
later compared with those who reported a low level of
baseline physical activity. This relationship was strongest
for patients with hypertension, Type I diabetes, chronic
heart failure, and depression (45). In addition to these epi-
demiological observations, experimental evidence is useful
in understanding relationships between physical activity and
the moods of energy and fatigue. Experiments overcome
some of the limitations inherent in large cross-sectional
studies (e.g., crude methods used to estimate physical ac-
tivity, inability to determine cause–effect relationships).
Physical inactivity. Complementary lines of experi-
mental evidence suggest a link between physical inactivity
and a worsening of feelings of energy and fatigue. Healthy
young men undergoing 20 d of experimentally induced bed
rest reported large increases (compared with the preinter-
vention assessment) of 2.1 standard deviations in the inten-
sity of fatigue feelings and decreases of 0.67 standard de-
viations in the intensity of energy feelings measured by the
POMS fatigue and vigor scales (22). In a study using a
different physical inactivity paradigm, 2 d of complete ex-
ercise deprivation among healthy women and men who
typically exercise 6–7 d·wk?1for 45 min·d?1resulted in
increases in the intensity of fatigue feelings of 0.43 standard
deviations and large decreases of 1.67 standard deviations
in the intensity of energy feelings as measured by the POMS
and comparedwith preintervention
Fatigued patients. Randomized controlled trials are
widely regarded as the gold standard design for determining
the efficacy and effectiveness of a medical or health inter-
vention such as increased physical activity. Randomized
controlled trials conducted with chronic fatigue syndrome
and fibromyalgia patients are not considered here because
these investigations typically have measured a wide array of
fatigue-related symptoms rather than energy or fatigue
moods per se (e.g., 51). The effect of 10–20 wk of increased
physical activity on the moods of energy and fatigue among
sedentary patients with fatigue-related medical conditions
has been examined in at least four randomized controlled
trial experiments that now will be summarized.
One randomized controlled trial examined the influence
of 10 wk of weightlifting exercise on energy feelings among
32 adults aged 60–84 yr who met the criteria for major or
minor depression or dysthymia (42). The participants were
randomly assigned to either a health education control con-
dition (1 h per session twice weekly) or progressive resis-
tance training of large muscle groups (thrice weekly, 45 min
per session, at an intensity of 80% of one repetition maxi-
mum). Feelings of energy were measured using the SF-36
vitality scale, and the results are illustrated in Figure 2.
Before the intervention, the depressed participants in both
groups reported less frequent energy feelings compared with
age norms (i.e., the mean ? SD for the relevant vitality
norms is 59.9 ? 22.1, and these data stem from a sample of
442 U.S. men and women between the ages of 65 and 74 yr)
(49). After the 10-wk intervention, those who exercised
reported a large increase in the frequency of energy feelings
of ?1.3 standard deviations. This increase was significantly
FIGURE 2—The influence of 10 wk of resistance exercise on prior
month frequency of energy-fatigue feelings among depressed older
adults compared with controls receiving health education; adapted
from Singh et al. (42). Copyright © The Gerontological Society of
America. Reproduced by permission of the publisher.
CHRONIC EXERCISE, FATIGUE, AND ENERGYMedicine & Science in Sports & Exercise?
greater than the small increase of ?0.14 standard deviations
observed for the control group.
A second randomized controlled trial examined the in-
fluence of 12 wk of aerobic exercise on energy feelings
among 25 heart failure patients (40). Participants were ran-
domly assigned to either a no treatment control condition or
to cycle ergometry and stepping exercises for 3 h·wk?1at
50% of maximal aerobic power. After the 12-wk interven-
tion, the mean SF-36 vitality score for the no treatment
control group decreased by a small, statistically insignificant
amount. In contrast, those who exercised reported large
increases of ?1 standard deviation in feelings of energy
compared with the preintervention baseline. The magnitude
of the increase in the frequency of energy feelings was
larger than any of the other quality of life indicators mea-
sured by the SF-36.
A third randomized controlled trial examined the influ-
ence of daily exercise on the intensity of “current day”
feelings of energy and fatigue among 62 cancer patients
with solid tumors or lymphomas who were undergoing
high-dose chemotherapy (16). Participants were randomly
assigned either to a no treatment condition or to 15 min of
daily cycle ergometry at a low intensity (mean ?SD power
output of 30 ? 5 W). The number of weeks of the exercise
program varied for each patient, and pre- and posttests were
conducted on the day of admission and the day of discharge
from the hospital. Moods were assessed using the POMS
questionnaire. As is common among cancer patients being
treated with chemotherapy, the patients in the control group
(N ? 32) reported significantly less intense feelings of
energy and significantly more intense feelings of fatigue on
the day of discharge compared with the day of admission.
The general direction of mood changes was the same in the
exercise group. However, these negative mood changes, and
especially the energy feelings, were attenuated (i.e., the
reduction in energy feelings with chemotherapy was not as
large) among the patients who completed the low intensity
daily exercise (N ? 27). The effect of exercise on energy
feelings in this experiment was ?0.5 standard deviations.
The fourth randomized controlled trial examined the in-
fluence of 20 wk of aerobic exercise on energy and fatigue
feelings among 228 primary care patients with persistent,
unexplained physical symptoms (39). Participants were ran-
domly assigned either to 1 h·wk?1of physiotherapist su-
pervised aerobic exercise or to the same amount of time
stretching. Participants also were asked to perform home-
based exercise or stretching for 20 min 3? wk?1. At base-
line, low SF-36 vitality scores characterized both the aerobic
exercise (27.2 ? 22.4) and stretching (26.9 ? 24.6) groups.
At the end of the program statistically significant and similar
increases in the frequency of energy feelings were reported
by both the aerobic exercise (35.9 ? 33.1, improvement of
?0.39 standard deviations) and stretching (39.7 ? 32.0,
improvement of ?0.52 standard deviations) groups.
In summary, results from the four randomized controlled
trials of the effects of exercise training on feelings of energy
and fatigue among people with a fatigue-related medical
condition were uniformly positive.
Healthy sedentary. At least 15 experiments have ex-
amined the influence of chronic exercise on energy and
fatigue moods in healthy sedentary people. A few of these
investigations were randomized controlled trials, but most
were quasiexperimental in design. The findings of these
studies have been mixed. About half of the studies showed
a moderate-to-large increase in feelings of energy in asso-
ciation with exercise training (e.g., 2,4,6,15,19,24,29,34),
whereas the others showed no meaningful change in feel-
ings of energy or fatigue (e.g., 3,5,8,12,19,21,25,35,44). A
representative example from among the better designed
investigations (e.g., large sample, random assignment, con-
trol condition) will be summarized. A total of 180 healthy
adults (aged 40–69 yr) were recruited and randomly as-
signed to one of five conditions: a Tai Chi–type physical
activity program, moderate-intensity walking, low-intensity
walking, low-intensity walking combined with listening to
audio taped instructions to relax, and a nonexercise control
condition. All the exercise programs were performed 3
d·wk?1for 45 min each session for 16 wk. Mood was
measured shortly before and after the conditions. Insignifi-
cant condition-by-time interactions were found for the
POMS energy and fatigue scale scores (8); thus, feelings of
energy and fatigue neither increased nor decreased with
exercise training to an extent more than would be expected
One credible explanation for the failure to consistently
find that increased chronic physical activity is associated
with improvements in the moods of energy and fatigue
among sedentary healthy adults is the presence of high
energy and low fatigue at the outset of the investigation. A
high level of energy at the outset makes it difficult for an
exercise intervention to have a positive effect on feelings of
Athletes. Experiments with endurance athletes have re-
vealed that physical activity can both improve and worsen
moods of energy and fatigue, and the effect depends on the
volume and intensity of the training stimulus. Large in-
creases and decreases in the volume and intensity of endur-
ance training repeatedly have been found to be associated
with changes in POMS vigor and fatigue scores in a dose–
response fashion (37). For instance, one investigation mon-
itored the mood of 186 female and male college swimmers
who progressively increased their training volume from ?4
to ?12 km·d?1over the first 5 months of the training season
(41). Monthly assessments of mood, illustrated in Figure 3,
revealed that as the training load progressively increased to
a peak in January the mean fatigue scores also progressively
increased to a peak in January (the magnitude of the increase
over the five months was large, ?1.4 standard deviations).
The vigor scores showed a progressive and large decrease
during the period of increased training (?1.1 standard de-
viations at the January nadir). These negative mood shifts
were reversed when the training stimulus was reduced.
These negative mood shifts are not reversed among those
athletes who become stale. The athletic staleness syndrome
is characterized by impaired athletic performance, increased
perceptual effort during standardized exercise bouts and
Official Journal of the American College of Sports Medicinehttp://www.acsm-msse.org
severe and long-lasting mood disturbances, including
chronic fatigue (37). The yearly incidence of the staleness
syndrome among college swimmers ranges from 5 to 10%,
and the lifetime prevalence of staleness among elite distance
runners ranges from 60 to 64% (37).
SUMMARY AND RECOMMENDATIONS
Feelings of low energy and fatigue are common, affecting
about one-quarter of large samples surveyed. These percent-
ages are higher in patients suffering from major medical
conditions. Feelings of high energy and low fatigue are
beneficial for numerous reasons, including their association
with good health, a high quality of life, and optimal cogni-
tive and physical performance. An intervention that im-
proved energy and fatigue moods, if it was safe and widely
adopted, would have a large, positive effect on public
health, medicine, and the associated health care costs.
The small body of key research findings reviewed here
provides several lines of convergent evidence to support the
hypothesis that there is a positive association between par-
ticipation in regular physical activity and feelings of high
energy/low fatigue. There is evidence that this relationship
has negatively accelerating dose–response characteristics
within the range of physical activity typically performed by
nonathletes. Moreover, there is evidence that the relation-
ship is stronger than other variables known to be related to
energy and fatigue moods such as body mass index and
chronic illness. This evidence implies that increased phys-
ical activity would be a more effective method for improv-
ing feelings of low energy and fatigue than other strategies
that would involve manipulating variables which have been
found to be less strongly related to these moods, such as
losing weight or reducing either smoking or alcohol
The available evidence from epidemiological studies and
randomized controlled trial experiments with medical pa-
tients suggests that sedentary people who feel fatigued are
likely to experience a moderate-to-large increase in feelings
of energy if they become regularly physically active. Be-
cause there appears to be no randomized controlled trials
that included in the design both a no treatment control group
and an attention (placebo) control group, the available evi-
dence is not strong enough to show that chronic physical
activity causes improvements in energy and fatigue mood
states among sedentary people who feel fatigued.
It is clear from the available evidence that not all people
experience improvements in the moods of energy and fa-
tigue in association with increased participation in regular
physical activity. Sedentary people characterized by high
energy and low fatigue have little room to improve these
moods, so exercise adoption would likely have little effect
on the energy and fatigue moods of these individuals. It is
important to recognize that long-duration or high-intensity
exercise, the type of exercise regimen that commonly is
completed by endurance athletes training for a competition,
can produce feelings of fatigue and low energy.
This review suggests a number of priorities for future
research, including: 1) randomized controlled experiments
that incorporate both a no treatment and an attention (pla-
cebo) type control group in order to learn whether exercise
training causes an improvement in energy and fatigue
moods states; 2) large randomized controlled experiments
conducted with fatigued, sedentary individuals as well as
those with medical conditions, especially depression, dia-
betes, heart failure, and hypertension; 3) experiments exam-
ining the degree of overlap and/or independence of the
effect of chronic exercise on feelings of energy and other
important mood states such as anxiety and depression; 4)
investigations aimed at examining the role, if any, of tran-
sient (i.e., lasting 3–5 h postexercise) mood responses to
acute bouts of exercise in the longer lasting improvements in
feelings of energy that are associated with the adoption of
regular physical activity for 10–20 wk; 5) experiments
documenting dose–response relations between changes in
feelings of energy and increased physical activity or exer-
cise training; and 6) experiments aimed at understanding the
biological correlates and mechanisms for changes in feel-
ings of energy and fatigue that occur with regular exercise
(43), and investigations comparing regular exercise with
other interventions that might be employed to improve feel-
ings of energy such as weight loss or either reduced smoking
or alcohol consumption.
The authors acknowledge the support of the North American
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