Endorphins and Exercise

Edited abstracts of some recent published scientific articles.


Aerobics Classes
----------------

1.    Acute mood changes occur with various forms of physical activity.
      Increased levels of endogenous opioids (endorphins) in response to
      exercise may mediate activity-induced shifts in mood state. Aerobics
      class participants aged 20-46 years received the opiate receptor
      antagonist naltrexone (which would block the effect of endorphins)
      and a placebo in randomized, double-blind crossover fashion on two
      separate occasions at the same 75-min high-intensity aerobics class.
      
      Mood states were assessed before and after each class, which were
      spaced 5 days apart.  Significant differences were observed in
      overall mood; with the placebo, mood states became calmer, more
      relaxed and pleasant, tending away from depression, anger and
      confusion.  Positive mood shifts did not occur when subjects were
      preloaded with naltrexone, suggesting that activity-generated mood
      changes are mediated through endorphinergic mechanisms. (Daniel,
      1992). 


Potential Benefits
------------------

2.    In this paper we discuss recent experimental and clinical findings
      which lead us to propose that prolonged rhythmic exercise can
      activate central opioid systems by triggering increased discharge
      from mechanosensitive afferent nerve fibers (Group III or A-delta)
      arising from contracting skeletal muscle. 

      We review evidence that supports the concept that many of the
      cardiovascular, analgesic, and behavioral effects of exercise are
      mediated by this mechanism and that the same or similar mechanisms
      are responsible for the central and peripheral effects of
      acupuncture. [Or lying on a bed of nails, etc...<g>]

      Based on this hypothesis, and supporting evidence from human and
      animal studies, we suggest a mechanism and a potential therapeutic
      role for exercise in the treatment of selected patients with
      disorders as diverse as hypertension, addiction, depression, and
      anorexia nervosa. (Thoren, 1990)


Aerobic (how hard, how long?) or Anerobic?
------------------------------------------

3.    Exercise-induced increases in the peripheral beta-endorphin
      concentration are mainly associated both with changes in pain
      perception and mood state and are possibly of importance in
      substrate metabolism. 

      A more precise understanding of opioid function during exercise can
      be achieved by investigating the changes in beta-endorphin
      concentrations dependent upon intensity and duration of physical
      exercise and in comparison to other stress hormones.  

      Published studies reveal that incremental graded and short term
      anaerobic exercise lead to an increase in beta-endorphin levels, the
      extent correlating with the lactate concentration.  During
      incremental graded exercise beta-endorphin levels increase when the
      anaerobic threshold has been exceeded or at the point of an
      overproportionate increase in lactate.  

      In endurance exercise performed at a steady-state between lactate
      production and elimination, blood beta-endorphin levels do not
      increase until exercise duration exceeds approximately 1 hour, with
      the increase being exponential thereafter.  beta-Endorphin and ACTH
      are secreted simultaneously during exercise, followed by a delayed
      release of cortisol.  

      These results support a possible role of beta-endorphin in changes
      of mood state and pain perception during endurance sports. In
      predominantly anaerobic exercise the behaviour of beta-endorphin
      depends on the degree of metabolic demand, suggesting an influence
      of endogenous opioids on anaerobic capacity or acidosis tolerance. 
      (Schwarz, 1992)

4.    Non-specifically trained volunteers (aged about 25 years) performed
      exhausting incremental graded exercise and 1-min anaerobic cycle
      ergometer exercise at 2-h intervals to investigate beta-endorphin
      behaviour dependent on exercise intensity and anaerobic metabolism. 
      Venous blood samples were collected prior and subsequent to exercise
      until 20 min of the recovery period, as well as in the graded
      exercise before and after exceeding the individual anaerobic
      threshold.  

      Lactate concentration, heart rate and perceived degree of exertion
      were also determined.  Both types of exercise led to significant
      increases in beta-endorphin with levels of endorphin approximately
      twice as high after graded exercise as the anaerobic test.  In both
      tests, there was a relationship between the maximum concentrations
      of beta-endorphin and lactate.  We therefore conclude that physical
      exercise with increasing or mostly anaerobic components leads to an
      increase in beta-endorphin, the extent correlating with the degree
      of lactate concentration.  (Schwarz, 1990)

5.    A small treatment group of previously sedentary, psychologically
      normal, and medically healthy middle-aged men trained for 4 months
      in a structured fitness program. The treatment group was compared
      with two age-matched groups: a jogger group and a sedentary group.
      (Lobstein, 1989)
      Venous blood was collected in the early morning after the subjects
      had been fasting for at least 12 h. Resting plasma beta endorphin
      decreased following the 4 months of exercise training in the
      treatment group.  The jogger and sedentary groups demonstrated no
      changes following the 4 months. 

      Aerobic fitness, measured by the maximal oxygen uptake (VO2max),
      increased from 36 to 45 ml.kg-1.min-1 in the treatment group after
      the 4 months of training. There were no changes in VO2max for either
      the jogger group or the sedentary group following the 4 months. 


6.    Relationship between the intensity of running exercise on a
      treadmill and the changes in the concentrations of beta-endorphin
      were studied in 10 experienced male endurance athletes.  At random
      order, the subjects run on a treadmill six exercises which required
      on an average 50, 58, 69, 80, 92 and 98% of their maximal oxygen
      consumption. 

      Plasma levels of beta-endorphin did not show any significant changes
      during the 50-80%-tests. During the 92% test, the mean levels
      increased significantly from 3.0 to 8.0 pmol/l, and during the 98%
      test, from 3.7 to 20.4 pmol/l. Increases in the plasma levels of
      beta-endorphin were always accompanied by an increase in the blood
      lactate level. 

      We conclude that intensive running with an anaerobic response causes
      an increase in the concentrations of beta-endorphin and ACTH in
      plasma in endurance athletes, whereas slight aerobic exercise did
      not elicit any response.  (Rahkila, 1988)

7.    During the past several years, excessive stress has come to be
      recognized as a threat not only to quality but also to length of
      life. There is increasing evidence that the emotionally distressed
      individual may have an increased susceptibility to a number of
      pathologic conditions. 

      Physical activity, in the form of aerobic exercise, is a very
      fruitful means for coping with stress. The popular forms of aerobic
      activities that are most often pursued in order to help general
      cardiovascular condition may, in effect, improve the mental health
      of the individual. There are no guarantees that if you follow these
      recommendations you will live longer. However, the life you live
      will be healthier, happier, more productive, and less stressful.
      (Cooper, 1986)

8.    Beta-endorphin and ACTH were determined in the peripheral blood of
      14 human volunteers exercising on a bicycle ergometer.  After 1 h of
      submaximal work below anaerobic threshold (AT), beta-endorphin and
      ACTH levels did not change from control conditions. 

      Eleven of the same 14 subjects performed an uninterrupted graded
      exercise test on the same bicycle ergometer until exhaustion. This
      time beta-endorphin and ACTH levels increased concomitantly with
      exercise of high intensity. The peak values of these hormones were
      reached within 10 min after stopping maximal exercise, coincided
      with lactic acid peak levels.  

      A rise in lactic acid levels above the anaerobic threshold always
      preceded the exercise-induced rise in beta-endorphin.  Within the
      population tested, two subgroups could be distinguished: one
      comprising individuals whose hormonal response nearly coincided with
      the rise in lactic acid (rapid responders) and a second group
      composed of subjects whose normal response appeared delayed with
      respect to the lactic acid rise (slow responders). 

      These results support the view that beta-endorphin and ACTH are
      secreted in equimolar quantities into the blood circulation in
      response to exercise, and suggest that metabolic changes of
      anaerobiosis play a key role in the regulation of stress-hormone
      release.  (de-Meirleir, 1986)

9.    The effects of intense exercise on pain perception, mood, and plasma
      endocrine levels in man were studied under naloxone (antagonist to
      the endorphin receptors)  and saline conditions. Twelve long-
      distance runners (mean weekly mileage = 41.5) were evaluated on
      thermal, ischemic, and cold pressor pain tests and on mood visual
      analogue scales (VAS) (simply like a "gas gauge" marked from no-pain
      to high pain which you mark to show relative level). 

      Blood was drawn for determination of plasma levels of beta-
      endorphin-like immunoreactivity before and after a 6.3 mile run at
      85% of maximal aerobic capacity. Subjects participated on two
      occasions in a double-blind procedure counterbalanced for drug
      order: on one day they received injections of naloxone following the
      run; on the other day, equal volume injections of normal saline. 

      Ischemic pain reports were significantly reduced post-run on the
      saline day, a hypoalgesic effect. Naloxone reversed the post-run
      ischemic but not thermal hypoalgesic effects. Joy, euphoria,
      cooperation, and conscientiousness VAS ratings were elevated post-
      run; naloxone attenuated the elevation of joy and euphoria ratings
      only. 

      The results show that long-distance running produces hypoalgesia and
      mood elevation in man. The effects of naloxone implicate endogenous
      opioid neural systems as mechanisms of some but not all of the run-
      induced alterations in mood and pain perception.  (Janal, 1984)


Experimental Model: Specifically--Pain
--------------------------------------

10.   Experimental pain thresholds (electrical intracutaneous finger and
      dental pulp stimulation) and plasma hormone levels (beta-endorphin,
      cortisol, and catecholamines) were measured in ten healthy sportive
      men before, during, and after progressively more strenuous physical
      exercise. 
      In a double-blind study conducted on two different days, 20 mg of
      the opioid-antagonist naloxone or placebo was administered prior to
      exercise.  A significant pain threshold elevation was found during
      exercise. Pain threshold elevation was most pronounced during
      maximal exertion, at which time the subjects reported the greatest
      subjective fatigue. Thresholds remained elevated 10-15 min after the
      end of exercise, and, 60 min after exercise, thresholds returned to
      baseline values. 

      Plasma beta-endorphin increased significantly during exercise.
      Plasma beta-endorphin levels did not correlate significantly with
      pain thresholds.  Naloxone failed to affect pain thresholds,
      although beta-endorphin increased significantly more during exercise
      after naloxone. <Now that is interesting - if you block the
      receptors, wouldn't you expect to get more produced...?>

      It is concluded that short-term, exhaustive physical exercise can
      evoke a transient elevation in pain thresholds. This exercise-
      induced elevation in pain threshold does not, however, appear to be
      directly related to plasma endorphin levels.  (Droste, 1991)



References
----------

Cooper-K-H. Gallman-J-S. McDonald-J-L Jr.
Role of aerobic exercise in reduction of stress.
Dent-Clin-North-Am. 1986 Oct. 30(4 Suppl). P S133-42. 

Daniel-M. Martin-A-D. Carter-J.
School of Kinesiology, Simon Fraser University, Burnaby, British Columbia,
Canada.
Opiate receptor blockade by naltrexone and mood state after acute physical
activity.
Br-J-Sports-Med. 1992 Jun. 26(2). P 111-5.

de-Meirleir-K. Naaktgeboren-N. Van-Steirteghem-A. Gorus-F. Olbrecht-J.
Block-P.
Academic Hospital, Vrije Universiteit Brussels, Belgium. 
Beta-endorphin and ACTH levels in peripheral blood during and after
aerobic and anaerobic exercise.
Eur-J-Appl-Physiol. 1986. 55(1). P 5-8.

Droste-C. Greenlee-M-W. Schreck-M. Roskamm-H.
Benedikt Kreutz Cardiovascular Rehabilitation Center, Bad Krozingen,
Germany.
Experimental pain thresholds and plasma beta-endorphin levels during
exercise.
Med-Sci-Sports-Exerc. 1991 Mar. 23(3). P 334-42.

Janal-M-N. Colt-E-W. Clark-W-C. Glusman-M.
New York State Psychiatric Institute, New York.
Pain sensitivity, mood and plasma endocrine levels in man following long-
distance running: effects of naloxone.
Pain. 1984 May. 19(1). P 13-25.

Lobstein-D-D. Ismail-A-H.
Department of Health Promotion, University of New Mexico, Albuquerque
87131.
Decreases in resting plasma beta-endorphin/-lipotropin after endurance
training.
Med-Sci-Sports-Exerc. 1989 Apr. 21(2). P 161-6.

Rahkila-P. Hakala-E. Alen-M. Salminen-K. Laatikainen-T. 
Department of Health Sciences, University of Jyvaskyla, Finland. 
Beta-endorphin and corticotropin release is dependent on a threshold
intensity of running exercise in male endurance athletes. 
Life-Sci. 1988. 43(6). P 551-8.

Schwarz-L. Kindermann-W.
Department of Sports and Performance Medicine, University of Saarland,
Saarbrucken, Federal Republic of Germany.
Changes in beta-endorphin levels in response to aerobic and anaerobic
exercise.  88 Refs.
Sports-Med. 1992 Jan. 13(1). P 25-36.

Schwarz-L. Kindermann-W.
Department of Sports and Performance Medicine, University of Saarland,
Federal Republic of Germany.
Beta-endorphin, adrenocorticotropic hormone, cortisol and catecholamines
during aerobic and anaerobic exercise. SO Eur-J-Appl-Physiol. 1990.
61(3-4). P 165-71.

Thoren-P. Floras-J-S. Hoffmann-P. Seals-D-R.
Department of Physiology, University of Goteborg, Sweden. 
Endorphins and exercise: physiological mechanisms and clinical
implications.
Med-Sci-Sports-Exerc. 1990 Aug. 22(4). P 417-28.  165 Refs


Contributed by Michael Williams, 72301,2647