Biomedical subjects

O M Rutherford

Publications and source records attributed to O M Rutherford.

34 records · Page 2Linked to original sources

PubMed1993

Spine and total body bone mineral density in amenorrheic endurance athletes.

Lumbar spine, total body, and regional bone mineral densities (BMDs) were measured in eumenorrheic and amenorrheic runners and triathletes by using dual-energy X-ray absorptiometry (Lunar DPX). Values were also compared with age- and weight-matched reference data from the Lunar British database. The amenorrheic group had significantly lower lumbar spine (P = 0.003), arm (P = 0.018), trunk (P = 0.014), and total spine (P < 0.0001) BMDs compared with the eumenorrheic group and significantly lower lumbar (P = 0.002) and total spine (P < 0.001) values compared with the reference controls. Leg (P = 0.009) and arm (P < 0.001) densities were significantly higher than controls. All regions, apart from the lumbar spine, were significantly higher in the eumenorrheic group compared with the reference group. There were no within-group differences for the runners and triathletes. Compared with the eumenorrheic athletes, the amenorrheic women had significantly later age of menarche (P = 0.0032). The type of physical activity undertaken by these athletes can compensate for the loss of menses at the majority of skeletal sites with the exception of the spine.

Adult↗

PubMed1992

Measurement of fibre pennation using ultrasound in the human quadriceps in vivo.

Real-time ultrasound scanning was used to measure the angles of fibre pennation of vastus lateralis (VL) and vastus intermedius (VI) of the human quadriceps (n = 12) in vivo. The maximum isometric force and cross-sectional area of the quadriceps were also measured. With the knee at right-angles the mean fibre angles for VL and VI respectively were 0.133 (0.021) rad [7.6 degrees (1.2 degrees)] and 0.143 (0.028) rad [8.2 degrees (1.6 degrees)] [mean (SD)], which is within the range of angles measured on cadavers. The mean angle decreased in going from the contracted [VL, 0.244 rad (14 degrees); VI, 0.279 rad (16 degrees)] to the stretched [VL, 0.105 rad (6 degrees); VI, 0.122 rad (7 degrees)] position. There was a significant positive correlation between fibre angle and muscle cross-sectional area but no relationship between fibre angle and force per cross-sectional area. No increase in fibre angle was detected after 3 months strength training. We conclude that ultrasound can be used to measure pennation angles of superficial muscle groups but we could not demonstrate a relationship between pennation and force-generating capacity.

Exercise↗

PubMed1992

The relationship of muscle and bone loss and activity levels with age in women.

Quadriceps strength and cross-sectional area (CSA), spine bone mineral density (BMD), bone mass in the mid- and distal femur and physical activity levels were measured in 216 healthy British women. Muscle strength, CSA and bone in the distal femur decreased linearly from the third decade. Cortical bone at mid-femur was maintained until the sixth decade. Spine BMD decreased from the fourth decade with an accelerated period of loss in the sixth decade. There were significant positive relationships between quadriceps strength and bone mass at all three skeletal sites. With age kept constant, physical activity levels did not correlate with any of the muscle or bone indices. The force-generating capacity of the quadriceps decreased with age. These results suggest a relationship between the loss of muscle and bone with age which cannot be explained by declining physical activity levels.

Adult↗

PubMed1991

Changes in skeletal muscle and body composition after discontinuation of growth hormone treatment in growth hormone deficient young adults.

OBJECTIVES: The aim of this study was to determine whether there are any changes in skeletal muscle strength and size and body composition following growth hormone (GH) withdrawal in GH deficient young adults. DESIGN: A longitudinal, 1-year, open, uncontrolled study of the changes in skeletal muscle and body composition following GH withdrawal was performed. Endocrine status was reassessed at the end of the study period during an insulin tolerance test. Some measurements were repeated after 2 years of treatment. PATIENTS: Twelve (11 male, one female; age range 14-21) patients who had been diagnosed during childhood as growth hormone deficient took part in the study. Four of the 12 patients were found to have a normal GH response on retesting at the end of the study and their results were analysed as a separate group. MEASUREMENTS: Quadriceps and forearm flexor maximum voluntary isometric strength, body fat content and serum IGF-1 were measured at 3-monthly intervals over 1 year. Every 6 months muscle size was measured from computerized tomography scans and fibre area from quadriceps needle biopsy samples. RESULTS: For the growth hormone deficient group the 12 month quadriceps strength, size and fibre areas were 94.0% +/- 8.5 (mean +/- SD), 94.5% +/- 6.3 and 85.6% +/- 17.7 respectively of control (baseline) values. Forearm flexor strength and size were 101.4% +/- 7.9 and 92.0% +/- 9.2 of control. Body fat percentage had increased from 19.5% +/- 8.6 to 24.1% +/- 9.5. No change was seen in the non-growth hormone deficient group. CONCLUSIONS: Although the changes measured were relatively small they suggest a role for GH in the maintenance of muscle integrity and body composition in the young adult with growth hormone deficiency.

Adolescent↗

PubMed1991

Human quadriceps strength and fatiguability in patients with post viral fatigue.

Quadriceps isometric strength, activation and fatiguability were measured in 11 patients with symptoms of fatigue three months after glandular fever or a glandular fever-like illness. Predicted normal and lower limits of normal muscle strength were calculated from height and age. These measures and the fatigue index were compared with a group of healthy students of similar age. Two of the patients were unable to activate fully their muscles. After allowing for this inhibition the group mean (SD) strength was 104 (22%) of predicted. Although there was no significant difference in the fatigue index between the patients and the control group, there was a trend for the patients to show less fatigue than controls. There was no difference in the muscle results for those patients who were found to have Epstein-Barr virus infections and those who did not. The feelings of weakness and fatigue experienced by the patients could not be explained by either physiological muscle fatigue or lack of effort.

Adolescent↗

PubMed1990

Long-lasting unilateral muscle wasting and weakness following injury and immobilisation.

Quadriceps strength and size was measured in a small group of subjects (n = 7) 1 to 5 years after full mobilisation following some form of unilateral lower limb trauma. The mean maximum voluntary isometric force (MVC) was significantly lower for the injured (I) compared to the uninjured (UI) leg (369 N +/- 139 vs. 535 N +/- 131, p less than 0.01). Electrical stimulation superimposed on the voluntary contractions demonstrated that all subjects were able to maximally activate the quadriceps of both legs. Mean quadriceps cross-sectional area (CSA) was significantly lower in the I (64 cm2 +/- 12.8) compared to the UI leg (80 +/- 12.8, p less than 0.01). One subject with marked unilateral weakness and wasting took part in a 3-month strength training study for the injured leg. After training the I/UI ratio had been restored to nearly 100% (94% MVC; 88% CSA). These results would suggest that longer and more intensive physiotherapy is required in the immediate post-injury period to restore muscle strength and size to severely atrophied muscle.

Atrophy↗

PubMed1989

Changes in skeletal muscle after discontinuation of growth hormone treatment in young adults with hypopituitarism.

Skeletal muscle strength and size were measured for 1 year following discontinuation of human growth hormone (hGH) treatment in 11 patients with hypopituitarism. Quadriceps and forearm flexor maximum voluntary isometric strength and size were measured. At the end of the study, endocrine status was reassessed by an insulin tolerance test. Three of the 11 subjects were found to have normal hGH secretion and were not included in the analysis. At 12 months, quadriceps strength, size and fibre areas were 94.0 +/- 8.5%, 94.5 +/- 6.3% and 85.6 +/- 17.7% (mean +/- SD), respectively, of baseline values. Forearm flexor strength and size were 101.4 +/- 7.9% and 92 +/- 9.2% of control values. Although these changes are relatively small, they suggest a role for growth hormone in the maintenance of muscle in the adult.

Adolescent↗

PubMed1989

Physiological changes in skeletal muscle as a result of strength training.

The picture of training that emerges is of a process that can be divided into a number of phases. In the first phase there is a rapid improvement in the ability to perform the training exercise such as lifting weights which is the result of a learning process in which the correct sequence of muscle contractions is laid down as a motor pattern in the central nervous system. This phase is associated with little or no increase in the size or strength of individual muscles. The learning process appears to be very specific in that lifting weights makes better weight lifters but not better sprinters. The second phase is an increase in the strength of individual muscles which occurs without a matching increase in the anatomical cross-section. The mechanism for this is not clear but could be a result of increased neural activation or some change in the fibre arrangement or connective tissue content. The third phase starts at a point where scientific studies usually end, at about 12 weeks when non-athletic subjects are beginning to tire of the repeated training and testing. After this point, if training continues, there is probably a slow but steady increase in both size and strength of the exercised muscles. The stimulus for these changes remains enigmatic but almost certainly involves high forces in the muscle, probably to induce some form of damage that promotes division of satellite cells and their incorporation into existing muscle fibres. Our information on the effect of long-term training comes primarily from observations on elite athletes whose physique may well be the result of genetic endowment or the use or abuse of drugs. For the athlete or patient hoping to increase muscle size by weight training the best combination of intensity, frequency and type of exercise still remains a matter of individual choice rather than a scientific certainty.

Humans↗

PubMed1988

Changes in strength and cross sectional area of the elbow flexors as a result of isometric strength training.

Changes in strength and size of the elbow flexor muscles have been compared during six weeks of isometric strength training in six male and six female subjects. Isometric training of one arm resulted in a significant increase in isometric force (14.5 +/- 5.1%, mean +/- SD, n = 12). No differences were seen in the response of male and female subjects. The extent of the change was similar to that reported for training studies of other muscles, thus refuting the suggestion that the elbow flexors may be especially amenable to training. Biceps and brachialis cross-sectional area (CSA) was measured from mid-upper arm X-ray computerized tomography before and after training. Muscles increased in area (5.4 +/- 3.8%) but this was smaller than, and not correlated with, the increase in strength. The main change in the first six weeks of strength training was therefore an increase in the force generated per unit cross-sectional area of muscle. The arrangement of fibres in the biceps is nearly parallel to the action of the muscle and it is argued that the increase in force per unit cross-sectional area is unlikely to be due to changes in the pennation of the muscle fibres as has been suggested for other muscles.

Adult↗

PubMed1988

Contractile properties and fatiguability of the human adductor pollicis and first dorsal interosseus: a comparison of the effects of two chronic stimulation patterns.

We have developed a method for simultaneously measuring the isometric force of the adductor pollicis (AP) and first dorsal interosseus (FDI) muscles of the hand. Both muscles were found to have very similar force-frequency relationships, relaxation rates and fatigue indices. The effect of 2 patterns of chronic electrical stimulation on the force production, contractile properties and fatiguability of the AP and FDI were compared in 2 groups of 5 subjects. One pattern consisted of uniform 10 Hz stimulation and the other a random pattern containing a few high frequency bursts against an essentially low frequency background. Both patterns were found to increase the fatigue resistance of both muscles by approximately 30% and caused a smaller and less consistent shift in the force-frequency relationship such that more force was generated at low frequencies of stimulation. There was a decrease in both the maximum voluntary and tetanic force after stimulation with the uniform 10 Hz but not the non-uniform patterns. The maintenance of force with the latter pattern may be due to the presence of the high frequency bursts.

Adult↗

PubMed1988

Muscular coordination and strength training. Implications for injury rehabilitation.

Strength training is commonly used in the rehabilitation of muscles atrophied as a result of injury and/or disuse. Studies on the effects of conventional leg extension training in healthy subjects have shown the changes to be very task-specific to the training manoeuvre itself. After conventional leg extension training for the quadriceps muscle the major improvement was in weightlifting ability with only small increases in isometric strength. The maximum dynamic force and power output during sprint cycling showed no improvement. These results suggest that the major benefit of this type of training is learning to coordinate the different muscle groups involved in the training movement rather than intrinsic increases in strength of the muscle group being trained. Other studies have shown changes in strength to be specific to the length and speed at which the muscle has been trained. The implication for rehabilitation is that strength training for isolated muscle groups may not be the most effective way of increasing functional ability. As the major changes are task-specific it may be better to incorporate the training into task-related practice. This would have the advantage of strengthening the muscle groups affected whilst increasing performance in those activities which are required in daily life.

Humans↗

PubMed1987

Human muscle strength training: the effects of three different regimens and the nature of the resultant changes.

1. Increases in strength and size of the quadriceps muscle have been compared during 12 weeks of either isometric or dynamic strength training. 2. Isometric training of one leg resulted in a significant increase in force (35 +/- 19%, mean +/- S.D., n = 6) with no change in the contralateral untrained control leg. 3. Quadriceps cross-sectional area was measured from mid-thigh X-ray computerized tomography (c.t.) scans before and after training. The increase in area (5 +/- 4.6%, mean +/- S.D., n = 6) was smaller than, and not correlated with, the increase in strength. 4. The possibility that the stimulus for gain in strength is the high force developed in the muscle was examined by comparing two training regimes, one where the muscle shortened (concentric) and the other where the muscle was stretched (eccentric) during the training exercise. Forces generated during eccentric training were 45% higher than during concentric training. 5. Similar changes in strength and muscle cross-sectional area were found after the two forms of exercise. Eccentric exercise increased isometric force by 11 +/- 3.6% (mean +/- S.D., n = 6), and concentric training by 15 +/- 8.0% (mean +/- S.D., n = 6). In both cases there was an approximate 5% increase in cross-sectional area. 6. It is concluded that as a result of strength training the main change in the first 12 weeks is an increase in the force generated per unit cross-sectional area of muscle. The stimulus for this is unknown but comparison of the effects of eccentric and concentric training suggest it is unlikely to be solely mechanical stress or metabolic fluxes in the muscle.

Action Potentials↗

PubMed1986

The role of learning and coordination in strength training.

The central changes associated with a period of strength training have been investigated in a group of 32 young healthy volunteers. Subjects participated in one of three 12 week training programmes, which required different degrees of skill and coordination. Study 1 consisted of unilateral isometric training of the quadriceps with the contralateral leg acting as a control, the apparatus providing firm back support and a lap strap. In Study 2 training consisted of unilateral concentric leg-extension with back support and hand-grips. In Study 3 subjects performed bilateral leg-extension with no back support. Measurements of maximum voluntary isometric strength were made at 2-3 week intervals and a continual record was kept of the weights lifted in Studies 2 and 3. The largest increase in isometric force was seen for the trained leg in Study 1 (approximately 40%). There was no significant change in strength in the contralateral untrained leg. In Studies 2 and 3 there was a large increase in training weights (about 200%) associated with smaller increase in isometric force (15-20%). It is concluded that a large part of the improvement in the ability to lift weights was due to an increased ability to coordinate other muscle groups involved in the movement such as those used to stabilise the body. The importance of these findings for athletic training and rehabilitation is discussed.

Adult↗

PubMed1986

Strength training and power output: transference effects in the human quadriceps muscle.

The effects of strength training of the quadriceps on peak power output during isokinetic cycling has been investigated in group of 17 young healthy volunteers. Subjects trained by lifting near-maximal loads on a leg extension machine for 12 weeks. Measurements of maximal voluntary isometric force were made at 2-3 week intervals and a continual record was kept of the weights lifted in training. Peak power output was measured at 110 rev min-1 and at either 70 or 80 rev min-1 before and after the 12 week training period. Measurements of maximum oxygen uptake (VO2max) were made on 12 subjects before and after training. The greatest change was in the weights lifted in training which increased by 160-200%. This was accompanied by a much smaller increase in maximum isometric force (3-20%). There was no significant change in peak power output at either speed. The VO2max remained unchanged with training. The role of task specificity in training is discussed in relation to training regimes for power athletes and for rehabilitation of patients with muscle weakness.

Adolescent↗

PubMed1986

Clinical and experimental application of the percutaneous twitch superimposition technique for the study of human muscle activation.

The use of percutaneous stimulation for twitch superimposition in the human quadriceps has been compared with stimulation via the femoral nerve. It was found that the relationship between the extra force generated by the twitch and the level of voluntary contraction was independent of the percentage of the muscle stimulated. The technique was used to study activation of the quadriceps and biceps in a group of young healthy adults, and quadriceps activation in patients with musculo-skeletal disorders. The majority of subjects could fully activate their muscles during brief isometric contractions. Inhibition was demonstrated in patients with muscle pain and joint pathology and in subjects with a previous history of knee or joint injury. The technique is easy to use and provides a simple way of detecting inhibition where it might not be anticipated, such as in the absence of pain. Where inhibition is demonstrated the technique can be used to predict approximately the maximum force available.

Adolescent↗

PubMedDate not supplied

The human force:velocity relationship; activity in the knee flexor and extensor muscles before and after eccentric practice.

The human voluntary force:velocity relationship frequently fails to demonstrate the expected high eccentric forces. Possible explanations include unique activation strategies which might be affected by neural learning mechanisms. We investigated the effect of practicing eccentric contractions on (1) the force:velocity relationship of the human knee extensor muscles and (2) the extent of agonist and antagonist muscle activity. Eight healthy adults [seven women, group mean age 31 (SEM 5) years +/-] practiced twice a week for 4 weeks using their non-dominant legs. Each session comprised three isokinetic concentric and eccentric maximal voluntary contractions (MVC) at randomised angular velocities of 100, 200 and 300 degrees.s-1. Before and after, the force:velocity relationship was determined bilaterally (angular velocities 0-300 degrees.s-1). There were no significant differences in the forces generated or relative electromyogram (EMG) activity after practice, although there was a trend for dynamic forces to increase. Beforehand, the bilateral eccentric MVC forces were lower than isometric (P < 0.0025); afterwards they were broadly similar. The agonist EMG was similar during isometric and eccentric contractions, but lower during concentric (P < 0.03). Antagonist EMG activity showed considerable individual variation, was similar during all contraction types and tended to be greater during dynamic contractions. These data indicate that neither central learning mechanisms nor total muscle activation strategies underlie the human failure to produce the expected high eccentric voluntary forces in humans.

Adult↗