Affective Responses To Exercise

Exercise can influence how people feel. This observation  has  attracted  considerable  research  attention in the last 50 years. There are several reasons for this. First, if exercise can improve how people feel,  this  could  have  significant  implications  for mental health. Disorders impacting mood (depression,  dysthymia,  bipolar  disorder)  and  anxiety (generalized anxiety, phobia, posttraumatic stress) are  prevalent  and  can  have  a  devastating  effect on  quality  of  life  for  sufferers  and  their  families. Moreover,  standard  therapies  such  as  pharmacotherapy  and  psychotherapy  are  costly  and  not always  effective.  Psychoactive  drugs  in  particular can  have  several  undesirable  side  effects.  Against this  backdrop,  exercise  offers  the  promise  of  an intervention  that  can  be  effective  (by  some  estimates,  at  least  as  effective  as  the  standard  forms of  therapy),  inexpensive,  free  of  undesirable  side effects, and associated with many additional benefits for the body (e.g., reduced cardiovascular risk) and mind (e.g., reduced risk for dementia).

Third, the low adherence to exercise represents a major public health problem. Most people who become physically active either do not exercise regularly or quit. Although most contemporary theories  assume  that  nonadherence  and  drop-out  are the  result  of  a  rational  decision-making  process, these phenomena may also be driven by affective processes.  Affect  is  a  powerful  motive  in  human behavior.  People  may  adhere  to  exercise  if  their affective responses are positive and may drop out if  their  affective  responses  are  consistently  negative. This possibility, which has received empirical support,  offers  researchers  new  insight  into  the mechanisms underlying exercise behavior.

History

The  first  studies  on  affective  responses  to  exercise appeared in the late 1960s. The typical methodological  approach  consisted  of  administering a  questionnaire  of  mood  (such  as  the  Profile  of Mood  States)  or  anxiety  (such  as  the  State-Trait Anxiety  Inventory)  shortly  before  and  after  an exercise bout. At the time, very few questionnaires were designed to assess nonclinical forms of how people  feel.  Therefore,  the  limited  availability  of measures  dictated  the  dependent  variables  being studied.  Consequently,  those  variables  might  or might not have been the most relevant, raising the possibility that changes also occurred in variables other than those being measured. The samples of respondents  typically  consisted  of  conveniently accessible  groups,  such  as  young,  healthy,  physically active, and fit university students. The intensity of exercise was rarely monitored via objective means (electrocardiography or expired gases) and, when it was standardized across participants, the method was often based on estimated, rather than directly measured, maximal exercise capacity (typically, age-predicted maximal heart rate, known to result in considerable errors). Despite these methodological limitations, which were consistent with a  nascent  line  of  research,  early  studies  provided voluminous  evidence  of  an  exercise-associated anxiolytic and mood-enhancing effect.

Mechanisms

In the 1980s and 1990s, along with numerous replications  of  the  anxiolytic  and  mood-enhancing effects across different settings, samples, and types of  exercise,  research  attention  turned  to  mechanistic  hypotheses.  These  included  proposals  that exercise makes people feel better because (a) they perceive  that  they  are  doing  something  challenging  and,  at  the  same  time,  beneficial  (the  mastery  hypothesis);  (b)  it  provides  an  opportunity to  temporarily  escape  the  stresses  and  hassles  of daily life (the distraction or time-out hypothesis); (c) it provides an opportunity for enjoyable social interaction  (the  social  interaction  hypothesis); (d) it corrects imbalances in monoaminergic neurotransmission  that  are  associated  with  negative affectivity (the monoamine hypothesis); (e) it promotes the release of peripheral and central endogenous  opioids  (the  endorphin  hypothesis);  and (f) it raises core temperature, which creates a sense of  relaxation  or  exhilaration  (the  thermogenic hypothesis).

The conclusions from these investigations have been  mixed.  What  seems  clear  is  that  no  single explanation  can  provide  an  exclusive  account  of the reasons why exercise can make people feel better. Studies on the mastery hypothesis have demonstrated that participants whose physical confidence is  strengthened  report  feeling  better  than  those whose  physical  confidence  is  weakened.  On  the other  hand,  the  thermogenic  hypothesis  has  been largely  discredited,  with  studies  demonstrating that elevations in core temperature during exercise are  associated  with  feeling  worse,  not  better.  The endorphin  hypothesis  continues  to  hold  promise. However, interest in this idea has declined following  a  string  of  studies  that  produced  conflicting results and, thus, confusion and frustration among researchers.  However,  upon  closer  analysis,  the inconsistencies can be attributed to methodological weaknesses,  which,  in  turn,  could  be  due  to  the lack  of  interdisciplinary  expertise  on  the  physiology  and  pharmacology  of  the  endogenous  opioid system.  The  distraction  and  social-interaction hypotheses  may  provide  partial  explanations,  but there are caveats for both. Specifically, while other distracting activities may also produce a feel-better effect,  exercise  often  produces  changes  that  are qualitatively  different.  For  example,  while  a  session  of  meditation  or  a  period  of  quiet  rest  may primarily induce relaxation, a typical response to a bout of moderate-intensity exercise consists of an increase  in  perceived  energy  during  and  immediately following the bout and, only later, an increase in  relaxation  compared  to  baseline.  Furthermore, while an enthusiastic and supportive social group can enhance the positive affective response to exercise, an indifferent group may experience no effect and a group or an exercise leader perceived as critical  can  have  a  negative  effect.  Moreover,  studies have shown that people can feel better even when they exercise in an empty room while staring at a barren  wall.  The  monoamine  hypothesis  remains viable,  with  findings  showing  that  monoamines (serotonin,  dopamine)  may  be  implicated  in  the feel-better  effect.  However,  at  least  for  now,  this research is limited to experimental animals, with all the interpretational challenges that this entails, that is, inability to directly extrapolate from observable animal behavior to subjective human feelings.

Mechanistic  research  has  now  moved  in  some notable  new  directions.  First,  studies  have  begun exploring associations between affective responses to   exercise   and   neurotransmitter   dynamics. Advances  in  positron  emission  tomography  have made  it  possible  to  quantify  exercise-associated changes in receptor occupancy in the human brain. Second, research is emerging on the role of endocannabinoids,  a  class  of  substances  discovered relatively recently, that are extensively involved in reward.  Both  experimental  studies  with  animals and  preliminary  correlational  studies  of  peripherally  circulating  endocannabinoids  in  humans  suggest that these substances may add one more piece to the mechanistic puzzle. Third, research is examining the role of exercise-upregulated neurotrophic factors  in  anatomical  adaptations  in  the  human brain that may be associated with how people feel. While  chronic  psychological  stress  is  associated with reduced synthesis of neurotrophic factors and reduced  volumes  of  brain  structures  involved  in emotion  and  mood  regulation,  exercise  is  among the most potent known stimuli for the upregulation of these neurotrophic factors.

Beyond the Feel-Better Effect

Critics express skepticism about the ability of exercise to make people feel better based on a simple but intriguing argument: If exercise could, in fact, make people feel better, would most people be sedentary? Research based on a new methodological platform is beginning to show that the feel-better effect, while feasible, is neither automatic nor guaranteed for everyone. It should more accurately be described as conditional.

One  of  the  methodological  innovations  was the  introduction  of  measures  that  tap  the  main dimensions of affect, as opposed to a few discrete affective  states.  Theoretically,  the  advantage  is  no major variant of affective experience resulting from exercise (including negative variants) can go undetected. A second aspect of the revised methodology is the timing of affect assessments. It became clear that, by measuring only before and after the exercise bout, the shape of the affective response could be misrepresented. For example, depending on the intensity of exercise, pleasure could be reduced during exercise but rebound postexercise. However, if affect  is  assessed  only  before  and  after  the  bout, one could conclude that the only change was a pre-to-post  increase  in  pleasure.  Thus,  newer  studies have employed repeated assessments of affect, both during  and  after  the  bout.  Thirdly,  newer  studies use more accurate methods for standardizing exercise intensity, reducing error variance and increasing statistical power. The measurement of expired gases has become common practice. Furthermore, several  laboratories  base  the  standardization  of intensity on the more laborious but more meaningful  practice  of  identifying  physiological  markers, such as the ventilatory or lactate threshold and the respiratory  compensation  point.  These  markers differ among individuals, even of the same sex, age, health  status,  activity  habits,  and  aerobic  capacity.  Research  suggests  that  exercising  at  intensities  slightly  above  and  below  these  markers  may be  associated  with  considerable  differences  across several physiological systems as well as differences in affective responses. Finally, once it became clear that affective responses varied between individuals, even  in  response  to  the  same,  well-standardized, exercise  stimulus,  it  also  became  apparent  that analyses of change restricted to the level of entire groups  could  be  misleading.  This  is  because  subgroups within the same sample may respond in different  directions  (e.g.,  increased  versus  decreased pleasure). Thus, it is possible for two subgroups to exhibit changes of equal magnitude but in opposite directions, resulting in a group mean that appears unchanged  over  time.  In  such  cases,  the  sample mean  fails  to  reflect  the  actual  response  of  individuals, becoming merely a statistical abstraction. To address this problem, in newer studies, change is examined both at the level of the entire sample and at the level of individuals and subgroups.

The  conclusion  from  studies  based  on  this revised  methodology  is  that  the  feel-better  effect represents  only  one  aspect  of  the  multifaceted exercise–affect relationship. Interindividual differences are prevalent and reductions in pleasure are common. For example, obese and inactive middle age  women  report  declines  in  pleasure  across  the entire range of exercise intensity.

Affective Responses and Exercise Prescription

The  optimization  of  affective  responses  to  exercise is gradually being adopted as one of the pillars of  exercise  prescription  guidelines,  alongside  the maximization  of  biological  adaptations  like  gains in fitness and health and the minimization of risk. Exercise practitioners are advised to systematically monitor the affective responses of participants and to regulate exercise intensity to ensure that affective responses remain positive or at least nonnegative. This  can  be  achieved  by  (a)  allowing  participants to self-select their intensity, in order to engender a sense of perceived autonomy and self-efficacy; and (b) ensuring that intensity does not greatly exceed the  ventilatory  threshold  (which  can  be  estimated without  instruments  as  the  level  of  intensity  that brings about a perceptible increase in the frequency and depth of ventilation and a subjective characterization of perceived exertion as “somewhat hard” or  “hard”).  Maintaining  proper  hydration  and comfortable  ambient  temperature  and  humidity levels is also important.

Furthermore,  it  is  crucial  to  recognize  that  the relationship  between  exercise  intensity  and  affective  responses  is  influenced  by  individual  differences.  Because  of  a  combination  of  genetic  and epigenetic  factors,  people  develop  varied  preferences for levels of exercise intensity and different degrees of tolerance to intense exercise. These differences influence the affective responses that individuals experience at different intensities. Although a standard method of tailoring exercise intensity to individual  levels  of  preference  and  tolerance  has yet  to  be  developed,  practitioners  should  keep  in mind  that  what  was  pleasant  for  one  participant may not be pleasant for another.

Finally, it is advisable to maintain a social environment  in  which  participants  can  feel  confident and  secure.  The  presence  of  other  exercisers  who appear to be of superior fitness or an exercise leader who emphasizes skill, appearance, or interpersonal comparisons  could  induce  social-evaluative  and self-presentational concerns.