Muscle fatigue is an exercise-induced reduction in maximal voluntary muscle force. It may arise not only because of peripheral changes at the level of the muscle, but also because the central nervous system fails to drive the motoneurons adequately. Evidence for “central” fatigue and the neural mechanisms underlying it are reviewed, together with its terminology and the methods used to reveal it. Much data suggest that voluntary activation of human motoneurons and muscle fibers is suboptimal and thus maximal voluntary force is commonly less than true maximal force. Hence, maximal voluntary strength can often be below true maximal muscle force. The technique of twitch interpolation has helped to reveal the changes in drive to motoneurons during fatigue. Voluntary activation usually diminishes during maximal voluntary isometric tasks, that is central fatigue develops, and motor unit firing rates decline. Transcranial magnetic stimulation over the motor cortex during fatiguing exercise has revealed focal cha...

Spinal and Supraspinal Factors in Human Muscle Fatigue

We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogene...

Skeletal muscle mass and distribution in 468 men and women aged 18–88 yr

The physiology of excitatory amino acids in the vertebrate central nervous system.

MEDICAL LITERATURE has been deluged during the past few years with books and papers on penicillin; but a book which has been produced under the general editorship of Sir Alexander Fleming himself represents a complete and authoritative summary of penicillin therapy as it stands today.' The book contains a series of independent contributions by \"experienced and eminent men who have worked with penicillin in Great Britain\". Their opinions and practical methods differ slightly, and there is some overlapping; but these are not disadvantageous, comparison and contrast lending interest to the reading. In the first or general section of the book Fleming contributes two chapters, one on the history and development of penicillin, introducing some interesting sidelights in the romance of discovery, the other on the bacteriological control of penicillin therapy. In both chapters the information is set out in meticulous detail and with a clarity and simplicity which can be enjoyed by all readers. Fleming also gives the right perspective to the place of penicillin amongst the antibiotics and lays down the principles of treatment. Both chapters are well illustrated and are the most outstanding in the book. Included in this first section also are chapters on the chemistry and manufacture of penicillin and its pharmacy, pharmacology and methods of administration. The second section of the book is entirely clinical, giving each author's view on the use of penicillin therapy in a disease or an infection of some particular region of the body. The entire range of peniCillin-sensitive conditions is considered in twenty authoritative and clearly written chapters; these contain many references and illustrations. Dental and veterinary diseases are also given fairly full consideration. The final section is a condensed resume of much of the preceding chapters and is written for. the general practttioner. This chapter is superttuous: it does not contain enough detall to be of much practical value. The book as a Whole, however, will undoubtedly be considered a classical contribution to medical literature and is strongly recommended, not only because of the general interest of its topic, but as a reference book on penicillin therapy of hitherto unequalled excellence. The typography, although conforming to war economy standards, is clear and the paper is good. There is an excellent list of references and the index is satisfactory.

Gray's Anatomy

Although loss of muscle mass is considered a cause of diminished muscle strength with aging, little is known regarding whether composition of aging muscle affects strength. The skeletal muscle atte...

Attenuation of skeletal muscle and strength in the elderly: The Health ABC Study.

The maximum voluntary force (strength) which could be produced by the knee-extensor muscles, with the knee held at a right angle, was measured in a group of healthy young subjects comprising twenty-five males and twenty-five females. Both legs were tested: data from the stronger leg only for each subject were used in the present study. Computed tomography was used to obtain a cross-sectional image of the subjects' legs at mid-thigh level, measured as the mid-point between the greater trochanter and upper border of the patella. The cross-sectional area of the knee-extensor muscles was determined from the image obtained by computer-based planimetry. The subjects' height and weight were measured. An estimate of body fat content was obtained from measurements of skinfold thicknesses and used to calculate lean body mass. Male subjects were taller (P less than 0.001), heavier (P less than 0.001), leaner (P less than 0.001) and stronger (P less than 0.001) than the female subjects. No significant correlation was found to exist between strength of the knee-extensor muscles and body weight in the male or in the female subjects. In the male subjects, but not in the female group, there was a positive correlation (r = 0.50; P less than 0.01) between strength and lean body mass. Muscle cross-sectional area of the male subjects was greater than that of the female subjects (P less than 0.001). The ratio of strength to cross-sectional area for the male was 9.49 +/- 1.34 (mean +/- S.D.). This is greater but not significantly so, than that for females (8.92 +/- 1.11). In both male and female groups, there was a significant (P less than 0.01) positive correlation between muscle strength and cross-sectional area. A wide variation in the ratio of strength to muscle cross-sectional area was observed. This variability may be a result of anatomical differences between subjects or may result from differences in the proportions of different fibre types in the muscles. The variation between subjects is such that strength is not a useful predictive index of muscle cross-sectional area.

Strength and cross‐sectional area of human skeletal muscle.

The relationship between the cross-sectional area (CSA) and maximum voluntary isometric strength of the knee extensor muscles was measured in a group of untrained subjects (control group, n=30), a group of successful marathon runners (n=6) and a group of successful sprinters (n=6). All subjects were male, aged between 20 and 41 years. In the control group muscle strength was found to be positively correlated with lean body mass (p<0.01) and with muscle CSA as determined by computed tomography scanning of the leg at mid-thigh level (p<0.001). However, in spite of these significant relationships, there was considerable variability between subjects. The sprinters were significantly stronger than the endurance runners (p<0.01), but neither of the athletic groups differed significantly from the control group. Muscle CSA was greater in the sprinters than in the marathon runners but this difference was not significant. The ratio of muscle strength to CSA in the control group varied from 7.07 to 13.57. All the trained subjects fell within this normal range, but the sprinters' muscles were stronger per unit CSA than the muscles of the marathon runners (p<0.05). Since it is well established that the leg muscles of sprinters contain a high proportion of fast twitch (FT) muscle fibres whereas endurance runners have a high proportion of slow twitch (ST) fibres, these results suggest that the strength which can be produced by a muscle may depend on its fibre composition. Variation in the distribution of the different fibre types in the untrained population may therefore account at least in part for the wide variability observed in this group.

Relationships between muscle strength and muscle cross-sectional area in male sprinters and endurance runners

This study has examined muscle strength and cross-sectional area in a group of 35 healthy untrained male subjects and 8 subjects who had been engaged in a strenuous weight-training programme. The maximum voluntary knee extension force which could be produced by the untrained subjects was 742 +/- 100 N (mean +/- SD). The trained subjects could produce a significantly (p less than 0.001) greater force (992 +/- 162 N). Cross-sectional area of the knee-extensor muscle group was 81.6 +/- 11.8 cm2 in the untrained subjects and 104.1 +/- 12.3 cm2 in the trained subjects (p less than 0.001). In the untrained subjects, a significant correlation existed between strength and muscle cross-sectional area (r = 0.56, p less than 0.001). In the same group of subjects, there was a significant inverse relationship between muscle cross-sectional area and the ratio of strength to cross-sectional area (r = 0.55, p less than 0.001). The mean ratio of strength to cross-sectional area was 9.20 +/- 1.29 for the untrained group whereas for the trained group this ratio was 9.53 +/- 1.01. It is suggested that the inverse relationship between strength per unit cross-sectional area and cross-sectional area results in part from an increased angle of pennation in the larger muscles.

https://bjsm.bmj.com/content/bjsports/18/3/149.full.pdf

Muscle strength and cross-sectional area in man: a comparison of strength-trained and untrained subjects.

1. Computed tomography has been used to establish the proportions of fat, muscle and bone present in the normal human forearm. 2. Subjects were healthy young volunteers, eight males and eight females. A series of six cross-sectional scans at right angles to the long axis of the forearm was obtained, the scans being made at equidistant intervals between the olecranon process and the ulnar styloid. 3. The volumes occupied by fat, muscle and bone were calculated for the complete forearm. Total forearm volume calculated by this method agreed closely with that measured by water displacement. 4. For the male subjects, forearm composition was 72.1 ± 4.4% muscle (mean ± SD), 15.0 ± 5.3% fat and 12.9 ± 1.2% bone. Female forearms had less muscle (P 5. Forearm muscle volume was significantly correlated (r= 0.75; P 6. Forearm fat content, as a percentage of total volume, was proportional to whole body fat content as estimated from skinfold thickness (males, r = 0.84; P

The relative proportions of fat, muscle and bone in the normal human forearm as determined by computed tomography.

The influence of a period of training, which lasts for several years, on the proportions of muscle, fat and bone present in the human forearm has been investigated by comparing trained and untrained limbs of nine experienced male tennis players. Ten healthy but untrained males of similar age served as a control group. Computed tomography (CT) scans of the forearm were made at intervals along its length to identify fat, muscle and bone and to calculate the volumes occupied by each of these components. Total forearm volume was greater in the dominant limb compared with the contralateral side in both trained (by 135 +/- 59 cm3, mean +/- SD, P less than 0.001) and untrained subjects (by 41 +/- 45 cm3, P less than 0.02). Forearm muscle volume was also greater in dominant limbs of trained (by 117 +/- 52 cm3, P less than 0.001) and untrained by 35 +/- 41 cm3, P less than 0.025) subjects. Muscle accounted for 75.4 +/- 2.7% of the total volume in the dominant arm of trained subjects compared with 71.4 +/- 4.2% in the control group (P less than 0.05). There was a greater proportion of muscle (P less than 0.05) and a smaller proportion of fat (P less than 0.001) in the trained limb compared with the contralateral limb of the same subjects. No differences in proportions of fat, muscle and bone were observed in dominant and non-dominant limbs of the control subjects. Trained subjects were able to exert a greater isometric force with the dominant limb (549 +/- 76N) than with the non-dominant limb (496 +/- 48N; P less than 0.005). There was no difference in grip strength between the arms of the untrained group (dominant: 516 +/- 107N; non-dominant: 491 +/- 91N). The ratio of strength to muscle volume was, however, the same in dominant and non-dominant arms of both groups of subjects.

J. S. Watson

Papers

Strength and cross‐sectional area of human skeletal muscle.

Relationships between muscle strength and muscle cross-sectional area in male sprinters and endurance runners

Muscle strength and cross-sectional area in man: a comparison of strength-trained and untrained subjects.

The relative proportions of fat, muscle and bone in the normal human forearm as determined by computed tomography.

Forearm composition and muscle function in trained and untrained limbs.