Differences in aerobic function and muscle size between ‘preferred’ and ‘non-preferred’ limbs and in healthy young males

Standard
It is often assumed that maximum aerobic function and muscle size is the same in right and left limbs in healthy subjects. This research paper by Anthony J Sargeant shows that this is not the case and significant differences exist between the preferred and non-preferred limbs. These are quite small in normal subjects but in subjects with a prior history of injury, even dating back many years, the differences can be large and persistent.
Subjects with such a history were excluded from this study.
Annals of Human Biology. 1977 Jan;4(1):49-55

Anthropometric data are presented for the preferred and non-preferred limbs of normal subjects together with measurements of one-limb maximum aerobic power output (V O2 max). The habitually preferred arms and legs were significantly larger in total volume (LV) when compared with the contralateral limbs (5 per cent, P less than 0-01; and 2 per cent, P less than 0-01 respectively). These differences were mainly attributable to variation in the size of the muscle component.

Expressed in absolute terms, V O2 max achieved in exercise with the preferred legs was significantly larger than the non-preferred legs (2-84 cf. 2-74 l/min; P less than 0-01) and a similar but non-significant difference was found between the arms (1-10 cf. 1-05 l/min). If, however, V O2 max is standardized for the size of the active muscle mass (LV, muscle plus bone) these differences between the preferred and non-preferred limbs disappear. The implications of these observations are discussed.

Advertisements

Muscle force following leg fracture, immobilization and muscle atrophy

Standard
This preliminary research report was made in a communication to The Physiological Society by Anthony J Sargeant in 1976. A full paper of this work was subsequently published in Clinical Science. It used strain gauges bonded to the cranks of a cycle ergometer to measure the asymmetry of forces exerted by an uninjured and an injured leg following fracture and consequent immobilization.
Journal of Physiology. 1976 Sep;260(2):12P-13P

Rebuilding leg muscle mass after injury

Standard
Professor Anthony J Sargeant carried out this research as part of his PhD in the early 1970s. It demonstrated that simple measurements of thigh muscle girth were fairly useless in assessing the magnitude of gross muscle atrophy and loss due to immobilization following leg fracture. In fact a subsequent study (published in Clinical Science by Anthony Sargeant in 1977) showed that even detailed anthropometric or X-ray measurements of muscle size greatly underestimated the actual loss at the muscle fibre level.
Annals of Human Biology. 1975 Oct;2(4):327-37

Anthropometric and X-ray data were collected on 20 young male patients undergoing a systematic programme of exercise therapy following fracture of the leg and consequent immobilization for 25–254 (mean 117) days. Estimates of total leg volume, calculated from X-ray or from anthropometric measurements, were essentially interchangeable in both the injured and uninjured legs. A procedure for estimating muscle volume from total leg volume is given.

At the start of rehabilitation, muscle volume was significantly smaller (860 ml, 16 per cent) in the injured than in the uninjured leg. By the end of rehabilitation (mean 50 days) the injured leg had siginficantly increased by 360 ml (8 per cent) over its initial volume, and the uninjured one had increased but not significantly (120 ml, 2 per cent), so that the injured leg was still approximately 11 per cent (620 ml) small than the uninjured. The initial degree of atrophy and the period of immobilization were not significantly correlated, although the latter showed a negative relationship (P greater than 0.05) with the rate of increase of muscle volume in the injured leg. No significant correlation was found between the ratio of injured/uninjured leg volumes and muscle width measurements at 1/3 subischial, at 12.7 cm above the knee joint space or at the maximum calf. In systematic studies involving atrophy muscle volume must therefore be estimated either by anthropometry or by X-ray measurements.

Prediction of Maximum Oxygen Uptake in patients with leg injury

Standard
Anthony J Sargeant carried out this research in 1975 at the Joint Services Medical Rehabilitation Unit at Chessington in Surrey. It was aimed at quantifying the aerobic function of the young men undergoing residential rehabilitation following leg fracture. Given the difficulty in some patients of making direct maximal measurements this study sought to look at the reliability of predictions of maximum function based on submaximal measurements (this study formed part of the PhD research of Tony Sargeant who was solely responsible for the collection, analysis of the data, and drafting of the paper for publication).
Archives of Physical Medicine and Rehabilitation. 1975 Aug;56(8):340-5

Procedures for the prediction of one-leg and two-leg maximal aerobic power output (VO2 max) have been examined in a group of 15 young men having had fracture of one leg and consequent immobilization resulting in muscle atrophy. Extrapolation of the submaximal cardiac frequency (FH) and oxygen intake (VO2) responses to an assumed FH amx of 175 in one-leg and 195 in two-leg work resulted in a systematic overestimation of VO2 max. This overestimation could be removed by applying the appropriate regression equations, but the overall accuracy of the extrapolation method was limited to +/- 15% in the case of the injured leg and +/- 8% for either the uninjured leg or both legs combined.

Prediction of VO2 max from leg muscle (plus bone) volume gave the same order of accuracy. However, it was shown that the VO2 max of the injured leg could be predicted with an accuracy of +/- 5%, if the observed VO2 max data of the uninjured leg and two legs were combined and utilized in the following formula: VO2 max (injured leg) = (A X 2) – VO2 max (uninjured leg), where A is the mean one-leg VO2 max predicted from the two-leg VO2 max observed. It was concluded that wherever possible the one-leg and two-leg VO2 max of patients undergoing rehabilitation therapy should be measured directly. If the patient is unable to pedal the bicycle ergometer with his injured leg alone then the VO2 max of this limb may be predicted from leg volume measurements or from the observed uninjured and two-leg VO2 max with an accuracy of approximately 8%.

Repeated contractions affect the geometry of muscle and hence the force generated

Standard
This study carried out by Costis Maganaris demonstrated how repeated contractions result in tendon creep – which by altering the geometry of human muscle changes the maximum force that is delivered.
Journal of Applied Physiology. 2002 Dec;93(6)

Abstract The aim of this study was to investigate the effect of repeated contractions on the geometry of human skeletal muscle. Six men performed two sets (sets A and B) of 10 repeated isometric plantarflexion contractions at 80% of the moment generated during plantarflexion maximal voluntary contraction (MVC), with a rest interval of 15 min between sets. By use of ultrasound, the geometry of the medial gastrocnemius (MG) muscle was measured in the contractions of set A and the displacement of the MG tendon origin in the myotendinous junction was measured in the contractions of set B.

In the transition from the 1st to the 10th contractions, the fascicular length at 80% of MVC decreased from 34 +/- 4 (means +/- SD) to 30 +/- 3 mm (P < 0.001), the pennation angle increased from 35 +/- 3 to 42 +/- 3 degrees (P < 0.001), the myotendinous junction displacement increased from 5 +/- 3 to 10 +/- 3 mm (P < 0.001), and the average fascicular curvature remained constant (P > 0.05) at approximately 4.3 m(-1). No changes (P > 0.05) were found in fascicular length, pennation angle, and myotendinous junction displacement after the fifth contraction. Electrogoniometry showed that the ankle rotated by approximately 6.5 degrees during contraction, but no differences (P > 0.05) were obtained between contractions. The present results show that repeated contractions induce tendon creep, which substantially affects the geometry of the in-series contracting muscles, thus altering their potential for force and joint moment generation.

Muscle fatigue and training following spinal cord injury

Standard

In this research programme supervised by Professor Anthony J Sargeant we were able to document some of the effects of training on the muscles of spinal cord injured people.

A spinal cord injury usually leads to an increase in contractile speed and fatigability of the paralysed quadriceps muscles, which is probably due to an increased expression of fast myosin heavy chain (MHC) isoforms and reduced oxidative capacity. Sometimes, however, fatigue resistance is maintained in these muscles and also contractile speed is slower than expected. To obtain a better understanding of the diversity of these quadriceps muscles and to determine the effects of training on characteristics of paralysed muscles, fibre characteristics and whole muscle function were assessed in six subjects with spinal cord lesions before and after a 12-week period of daily low-frequency electrical stimulation.

Relatively high levels of MHC type I were found in three subjects and this corresponded with a high degree of fusion in 10-Hz force responses (r=0.88). Fatigability was related to the activity of succinate dehydrogenase (SDH) (r=0.79). Furthermore, some differentiation between fibre types in terms of metabolic properties were present, with type I fibres expressing the highest levels of SDH and lowest levels of alpha-glycerophosphate dehydrogenase. After training, SDH activity increased by 76+/-26% but fibre diameter and MHC expression remained unchanged. The results indicate that expression of contractile proteins and metabolic properties seem to underlie the relatively normal functional muscle characteristics observed in some paralysed muscles. Furthermore, training-induced changes in fatigue resistance seem to arise, in part, from an improved oxidative capacity

Muscle weakness in Post Polio Syndrome is due to loss of muscle mass plus reduced activation

Standard

Abstract Quadriceps strength, maximal anatomical cross-sectional area (CSA), maximal voluntary activation (MVA), and maximal relaxation rate (MRR) were studied in 48 subjects with a past history of polio, 26 with and 22 without postpoliomyelitis syndrome (PPS), and in 13 control subjects. It was also investigated whether, apart from CSA, MVA and MRR were determinants of muscle strength. Polio subjects had significantly less strength, CSA, and MRR in the more-affected quadriceps than control subjects.

MVA was reduced in 18 polio subjects and normal in all controls. PPS subjects differed from non-PPS subjects only in that the MVA of the more-affected quadriceps was significantly lower. Both CSA and MVA were found to be associated with muscle strength. Quadriceps strength in polio subjects was dependent not only on muscle mass, but also on the ability to activate the muscles. Since impaired activation was more pronounced in PPS subjects, the new muscle weakness and functional decline in PPS may be due not only to a gradual loss of muscle fibers, but also to an increasing inability to activate the muscles.