Effects of strength training and immobilization on human muscle fibres

Abstract

Seven healthy male subjects were studied under control conditions and following 5-6 months of heavy resistance training and 5-6 weeks of immobilization in elbow casts. Cross-sectional fibre areas and nuclei-to-fibre ratios were calculated from cryostat sections of needle biopsies taken from triceps brachii. Training resulted in a 98% increase in maximal elbow extension strength as measured by a Cybex dynamometer, while immobilization resulted in a 41% decrease in strength. Both fast twitch (FT) and slow twitch (ST) fibre areas increased significantly with training by 39% and 31%, respectively. Immobilization resulted in significant decreases in fibre area by 33% for FT and 25% for ST fibres. The observed nuclei-to-fibre ratio was 10% greater following the training programme. However, this change was non-significant. There was also a non-significant correlation between the magnitude of the changes in fibre size and the changes in maximal strength following either training or immobilization.

Changes in muscle morphology in chronic trapezius myalgia.

“…The type I fibers belong to motor units which are the first to be recruited during repetitive movements of relativelylow tension (21). The larger area of the fibers in the patient biopsies, obtained from tender points, may reflect an adaptive response to frequent occupational use of this region of the muscle since muscular usage might cause an increase in fiber area (35,36). However, one might then expect the fiber size to be normalized in the patients since they had been on sick leave for a long period of time.…”

Adaptation of mechanical properties of muscle to high force training in man.

“…Isometric strength training of this type for [5][6][7][8][9][10][11][12] weeks produces increases in maximal force of 20 40 o (McDonagh, Hayward & 1)avies, 1983;Komi, Viitasalo, Rauramaa & Vihko, 1978). However, the increase in the cross-sectional area of whole muscle (Ikai & Fukunaga, 1970) and of single muscle fibres (MacDougall, Elder, Sale, Moroz & Sutton, 1980) is only one-quarter of the increase in the maximal voluntary contractile force (m.v.c). This is surprising, as muscle force should be directly proportional to the cross-sectional area of the muscle.…”

Myonuclei acquired by overload exercise precede hypertrophy and are not lost on detraining

“…There is no known mechanism for memory in muscle cells, and, to date, the longlasting effects of previous training have been attributed to motor learning in the central nervous system (3). However, it has been reported that muscles can remain hypertrophic after several months of detraining (1,(4)(5)(6)(7)(8). In one study on elderly individuals who had strength-trained, force was still 9-14% higher even after 2 y of detraining (7).…”