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1999 Publications

Can exercise-induced muscle damage be avoided?by M. McHughNISMAT, Lenox Hill Hospital, N.Y., N.Y. - last modified 2013-02-09 00:00
British Journal of Sports Medicine. 33(6):377, 1999.

 

All athletes have experienced the discomfort and debilitating effects of exercise-induced muscle damage. The symptoms are most commonly experienced at the beginning of the season when intense training is re-introduced following a period of relative inactivity. A plethora of scientific data is available describing exercise conditions resulting in exercise-induced muscle damage. It is well accepted that damage occurs with unfamiliar exercise, primarily involving eccentric contractions.

For example, downhill running places a large eccentric stress on the quadriceps muscle group and commonly results in muscle damage.1 However, muscles that have been preconditioned with eccentric contractions are protected against damage from subsequent bouts of eccentric exercise.

This is known as the repeated bout effect and has been demonstrated with various forms of exercise in both humans and in animal models.2 Despite the number of studies describing muscle damage and its various clinical symptoms, few studies have identified intrinsic causative factors or suitable interventions for limiting the symptoms.

Clinically, it is important to first identify individuals at risk of developing more severe symptoms and secondly to develop interventions which might limit those symptoms. Three recent experimental studies provide clinically relevant information for athletes and practitioners.3,4,5

Controlled experimental studies have demonstrated a high inter-individual variation in symptoms following a bout of unfamiliar eccentric exercise. These data indicate that some individuals are more susceptible to damage than others, but it is not clear why. McHugh et al recently demonstrated that musculoskeletal flexibility is an important factor affecting the severity of symptoms following eccentric exercise.3 Flexibility was quantified according to a measure of passive muscle stiffness and subjects were categorized as having "stiff", "normal" or "compliant" muscles.

Following a bout of eccentric exercise, subjects with stiff muscles experienced significantly greater strength loss, pain, muscle tenderness and elevation in plasma creatine kinase activity compared to subjects with compliant muscles. Greater apparent muscle damage was attributed to the inability of the tendon and aponeurosis of stiffer muscles to absorb the lengthening imposed by the eccentric contractions.

Warm-up and stretching are known to acutely reduce muscle stiffness.4 Since stiffness seems to predispose muscle to damage, it follows that appropriate pre-exercise warm-up may reduce the severity of subsequent exercise-induced muscle damage. Nosaka and Clarkson recently demonstrated that warm-up does, in fact, reduce subsequent symptoms of muscle damage.5

Eccentric contractions of the elbow flexors preceded by warm-up resulted in significantly less strength loss and elevation in plasma creatine kinase activity compared to eccentric contractions without prior warm-up. The protective effect was attributed to decreased passive muscle stiffness, although actual stiffness measurements were not made.

Besides the possible role of warm-up in limiting the symptoms of muscle damage, it is clear that preconditioning the muscle with eccentric contractions will provide a protective effect (repeated bout effect). Recent data suggest that it may not be necessary to damage the muscle with the initial bout in order to provide a protective effect.

Brown et al demonstrated that as few as 10 maximal eccentric contractions of the knee extensors were sufficient to markedly reduce symptoms following a subsequent bout of 50 maximal contractions, performed three weeks later. There was a clear repeated bout effect despite the fact that 10 contractions did not result in appreciable muscle damage.

These data indicate that preconditioning muscles with a few maximal eccentric contractions can markedly reduce symptoms following a subsequent, more intense, bout of eccentric exercise. The key elements for the repeated bout effect are that: (1) the preconditioning contractions are eccentric; (2) high intensity contractions are performed; and (3) the preconditioning contractions involve the same muscle groups that will be working eccentrically in the repeated bout.

In reality, all dynamic sports activities will involve a large component of high intensity eccentric contractions, whether the activity is in a game or practice situation. Athletes typically experience marked symptoms of muscle damage when returning to these activities following a prolonged lay off due to injury or following the off-season.

However, the severity of these symptoms may be reduced by: (1) maintaining good flexibility, especially of the principle muscle groups involved in the given sport; (2) preconditioning the principle muscle groups with a few high intensity eccentric contractions within one to two weeks prior to return to full activities; and (3) performing specific warm-up exercises for the principle muscle groups immediately prior to the first few training sessions or games.

Increasing the athlete's awareness of the cause of the symptoms will increase compliance with any intervention directed at limiting muscle damage. This is especially important in sports that do not place a large emphasis on warm-up or flexibility.

References:

Eston RG, Mickleborough J, Baltzopoulos V. Eccentric activation and muscle damage: biomechanical and physiological considerations during downhill running. Br J Sports Med 1995; 29:89-94.

McHugh MP, Connolly DAJ, Eston RG, Gleim GW. Exercise-induced muscle damage and potential mechanisms for the repeated bout effect. Sports Med 1999; 27:157-170.

McHugh MP, Connolly DAJ, Eston RG, Kremenic IJ, et al. The role of passive muscle stiffness in symptoms of exercise-induced muscle damage. Am J Sports Med 1999; 27:(5) in press.

Gleim GW, McHugh MP. Flexibility and the effects on performance and sports injuries. Sports Med 1997; 24:289-299.

Nosaka K, Clarkson PM. Influence of previous concentric exercise on eccentric exercise-induced muscle damage. J Sports Sci 1997; 15:477-483.

Brown SJ, Child RB, Day SH, Donnelly AE. Exercise-induced skeletal muscle damage and adaptation following repeated bouts of eccentric muscle contractions. J Sports Sci 1997; 15:215-222.