IS-PM04 - Exercise-induced muscle damage: What is it, how is it detected, and why is it induced?

INVITED SESSION: (IS-PM04) - Exercise-induced muscle damage: What is it, how is it detected, and why is it induced?
Date: 04.07.2019
Lecture room: Congress Hall
Time: 18:30 - 20:00

Chair(s): KAZUNORI NOSAKA - EDITH COWAN UNIVERSITY / AUSTRALIA

1. HISTOLOGICAL CHANGES IN MUSCLE FIBRES AND CONNECTIVE TISSUE AFTER ECCENTRIC EXERCISE: WHERE IS THE BORDER BETWEEN TOLERABLE DAMAGE AND RHABDOMYOLYSIS?
RAASTAD, T. / NORWAY

ABSTRACT:
There are characteristic changes in muscle ultrastructure observed after high-force exercise and ultra-endurance events that clearly demonstrate muscle damage in humans (1). The most frequently reported observations are minor to moderate changes in the myofibrillar structure involving disorganization of 1-20 adjacent sarcomeres (2). These changes are normally defined as muscle damage, but are also discussed as the first phase of a controlled remodelling process. More severe damage to muscle fibres involves segmental fibre necrosis and is related to more extreme exercise protocols involving unaccustomed maximal eccentric muscle actions (3). Segmental fibre necrosis is distinguished from the milder forms of damage and muscle fatigue by initiation of inflammation, slow recovery (more than 2 weeks) and very high levels of circulating muscle enzymes (e.g., CK) the days after exercise, and the more severe form of this phenomena is termed rhabdomyolysis. Disturbances in Ca2+ homeostasis is involved in several of the processes leading to fatigue, myofibrillar disorganization and necrosis after high-force exercise. Elevated Ca2+ in resting muscles is supposed to change tissue stiffness and changes in share modulus measured by elastography has consequently been suggested as one possible non-invasive method for early detection of muscle damage (4). This presentation will show the different types of ultrastructural changes and suggest how the different types of muscle damage can be indicated without muscle biopsies.
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2. NEURAL INHIBITION VERSUS DAMAGE EFFECTS: HOW CAN THEY BE DISTINGUISHED?
NICOL, C. / FRANCE

ABSTRACT:
This presentation will focus on the neuromuscular fatigue effects of stretch-shortening cycle (SSC) type exercises, which characterize natural, but exhaustive activities such as short and intensive or prolonged running and jumping exercises. Exhaustive SSC performances serve for the purpose to characterize more specifically the effects of repeated eccentric muscle actions on various aspects of the neuromuscular function.
Intensive and/or unaccustomed SSC exercises induce impairments of the neuromuscular function that are usually bimodal is nature. The “acute phase” is characterised by large drops in maximal voluntary contraction, rate of force development, voluntary EMG activity and stretch-reflex response leading to reduced maximal isometric and maximal SSC performances. A “temporary recovery” occurs after a couple of hours before the occurrence of large “secondary functional declines” and delayed onset muscle soreness (DOMS) that may last for a few days. Bimodal decrements are also reported in voluntary activation level and H/M reflex amplitude. Particularly important in terms of injury prevention is the timing of DOMS disappearance, as it occurs prior to complete structuro-functional recovery. It cannot therefore be used to reflect detailed recovery processes.
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3. SYMPTOMS AND MARKERS OF MUSCLE DAMAGE: WHAT CAUSES MUSCLE DAMAGE AND WHAT DETERMINES THE MAGNITUDE OF MUSCLE DAMAGE?
NOSAKA, K. / AUSTRALIA

ABSTRACT:
Muscles become weak, sore, stiff and occasionally swollen after unaccustomed exercise consisting of eccentric (lengthening muscle) contractions. These are generally considered as symptoms of muscle damage. Since pain, loss of function and swelling are cardinal signs of inflammation, it is likely that the symptoms are more associated with inflammation than damage itself.
In the presentation, I will try to clarify what muscle damage is, and explain the possible mechanisms underpinning muscle damage and the repeated bout effect, and discuss why muscle damage is induced by unaccustomed eccentric exercise.

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