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Biomedical subjects

C T Davies

Publications and source records attributed to C T Davies.

At least 37 records · Page 2Linked to original sources
PubMed1985

Effect of heating on the contractile properties of triceps surae and maximal power output during jumping in elderly men.

The electrically evoked contractile properties of the triceps surae and short-term (less than 2 s) maximal power output during vertical jumping have been examined before and after heating (by water immersion) in 5 elderly men aged 70 +/- 5 years. Leg immersion in water at 44 degrees C for 30 min produced a 3.4 degrees C rise in muscle temperature (Tm) and was associated with a significant (p less than 0.001) reduction in maximal time to peak tension and half relaxation time of the twitch, but was without affect on maximal twitch, tetanic (20 and 50 Hz) and voluntary tensions. However, at 10 Hz maximal tetanic tension was reduced (p less than 0.05) from 604 +/- 104 to 422 +/- 142 N. During vertical jumping from a force platform, peak power output (W) was significantly (p less than 0.05) increased from 1,155 +/- 212 to 1,381 +/- 307 W after heating. The rise in W was due to a small increase in both take-off velocity and the exerted force, and was reflected in a 3-cm increase in the height jumped from the force platform. It is concluded that the contractile characteristics of elderly triceps surae can be modified by heating and a rise in Tm does effect a change in the capacity of the muscle to generate power.

Aged↗
PubMed1984

A comparison of the mechanical properties of the first dorsal interosseous in the dominant and non-dominant hand.

The electrically evoked and voluntary contractile properties of the first dorsal interosseous muscle were measured on both hands in 10 healthy adults. The force of abduction of the index finger interosseous muscle was measured using a transducer resting against the lateral side of the proximal interphalangeal joint. The mean values of time to peak tension measured on the dominant hands were significantly slower than the values on the non-dominant hands (P less than 0.01) in a paired t-test. Maximal tetanic tension, maximal voluntary contraction strength, and maximal twitch tension are not significantly different. Fatigue indices on the dominant hands in each subject were higher than those on the non-dominant hands. The correlation coefficient between fatigue indices on the dominant and the non-dominant hand was 0.92 (P less than 0.01).

Adult↗
PubMed1984

Effect of diet on human muscle weakness following prolonged exercise.

The effect of altering muscle glycogen on the ability of skeletal muscle to generate voluntary and electrically evoked isometric force following prolonged exercise has been investigated in five healthy male subjects. Measurements from the triceps surae were made at rest, and before and after prolonged exercise (uphill walking) at approximately 75% VO2 max in low muscle glycogen (low CHO) and high muscle glycogen (high CHO) conditions. The results showed that before exercise there was no change in maximal twitch tension (Pto), maximal tetanic tension at frequencies of 10 (Po10), 20 (Po20) and 50 HZ (Po50), and maximal voluntary contraction (MVC) in low and high CHO compared with normal. The loss of force during a 2 min electrically evoked "fatigue test" at rest was found to be higher (p less than 0.05) in low CHO and lower (p less than 0.05) in high CHO than normal. Following the prolonged exercise, muscle weakness was produced in both low and high CHO conditions, but was found to be significantly greater in the low CHO condition for the measurements of Po10 (P less than 0.01), Po20 (p less than 0.05) and MVC (p less than 0.05). It is concluded that changes in muscle glycogen alone do not alter the isometric force generating capacity of human muscle, but when combined with prolonged exercise low muscle glycogen enhances exercise-induced muscle weakness.

Adult↗
PubMed1984

Effects of external loading on short term power output in children and young male adults.

The effects of external loading, in the form of small weights distributed evenly over the limbs and torso, on physical performance and power output have been studied during vertical jumping in 10 children and four young adults and the results compared with maximal cycling. The results show under control (unloaded) conditions the absolute peak power output (W) achieved by children and adults was 572 W (45%) and 765 W (25%) respectively higher in cycling than jumping. The addition of weights during jumping served only to increase this difference. External loading produced a linear decrease of W in both groups of subjects. The reduction in W was entirely due to a decrease of take-off velocity (VT). The relationship between VT and added weights (delta wt) could be described by the equations: VT (ms-1) = 1.91 - 0.042 delta wt (kg); r = -0.96 (children); VT (ms-1) = 2.49 - 0.021 delta wt (kg); r = -0.99 (adults). Thus, contrary to the recent work of Caiozzo and Kyle (1980) which involved stair-climbing, body size and speed of movement in children and young adults would appear to be optimally matched for the production of lifting work during vertical jumping. External loading reduces the generation of power output immediately prior to take-off of a maximal jump from a force platform.

Adult↗
PubMed1984

The effects of immobilization, after lower leg fracture, on the contractile properties of human triceps surae.

The contractile properties of the triceps surae were evaluated in 11 patients after unilateral fracture of the lower leg and subsequent immobilization for 135 +/- 68 days. Calf muscle cross-sectional area (plus bone: CSA) was assessed from anthropometric measurement. It was shown that the injured leg had a faster time to peak tension and increased half-relaxation time (1/2 RT); twitch force (Pt) was reduced by 25%. Evoked maximal tetanic tensions (Po) at 10 and 20 Hz were reduced by 51% and 46% respectively compared with the uninjured leg. The force of a maximal voluntary contraction (MVC) was also reduced, by 50%, but calf circumference and CSA were only 5% and 16% respectively lower in the injured leg. It was concluded that the changes in contractile speed may indicate a relatively greater atrophy of slow (type I) muscle fibres. The relationship between CSA and tension generation in the injured limb was shown to be poor after immobilization and during recovery. Anthropometric estimation of CSA does not appear to reflect the degree of muscle wasting, as indicated by reduced tension development after immobilization.

Adult↗
PubMed1984

The effects of short-term voluntary immobilization on the contractile properties of the human triceps surae.

In four male subjects one leg was immobilized in a full leg cast for 2 weeks. Measurements of the contractile properties of both triceps surae were made before, during and after immobilization. There was a significant increase in the mean twitch time to peak tension (Tc) after 1 week of immobilization from 126 +/- 10 ms to 143 +/- 20 ms (P less than 0.05) and in the half-relaxation time (T1/2r) from 88 +/- 7 ms to 107 +/- 12 ms (P less than 0.01). There were no further significant (P less than 0.1) changes in the twitch characteristics during the second week of immobilization. The strength of a maximal voluntary contraction (m.v.c.) declined by 11% (P less than 0.05) after 1 week and 24% (P less than 0.05) after 2 weeks. Twitch tension, tetanic tension and muscle fatigability were not significantly altered during immobilization. Muscle (plus bone) calf cross-sectional area (A) was reduced by 5% (P less than 0.01) after 1 week and a further 3% (P less than 0.05) after 2 weeks. The Tc and T1/2r of the twitch, m.v.c. and A returned to control values within 2, 7, 4 and 14 d respectively. No significant (P less than 0.01) changes were observed in the mechanical properties of the triceps surae of the contralateral limb during the period of immobilization. The results suggest that short-term voluntary immobilization is associated with atrophy and a diminished capacity of the muscle to develop maximal voluntary force.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1984

Different effects of ageing on the mechanical properties of human arm and leg muscles.

The effect of ageing on voluntary and electrically evoked muscle force was investigated. A group of 70-year-old men and a control group of young men took part in the study. The muscles studied were the elbow flexor group and the triceps surae group of the leg. With ageing both muscle groups showed a reduction in maximum voluntary force and in the force of electrically evoked tetani. The reduction was greatest in the leg muscles. The time to peak of the twitch was prolonged with age in the leg muscles. The findings are discussed in relation to the changes in fibre type known to occur in elderly muscle.

Adult↗
PubMed1983

Muscle function in children.

Electrically evoked mechanical and contractile properties of the triceps surae have been measured in 52 children aged 11 and 14 years, and results compared with previously reported data for adults (Davies and White 1982). The results show that the time to peak tension (TPT), half relaxation time (1/2RT) and supramaximal tension (Pt) of the twitch were not significantly (P greater than 0.1) different in girls and boys and independent of age. The 14-year-old girls and boys were stronger in terms of their supramaximal 10, 20, and 50 Hz tetanic tensions and maximal voluntary contraction (MVC) than their younger counterparts, and both groups of children were significantly (P less than 0.001) weaker than the young adults. However, if standardisation was made for an anthropometric estimate of calf muscle (plus bone) cross-sectional area (CSA), the differences in strength disappeared. Electrically stimulated and voluntary maximal force per unit CSA measured at the knee were 17.1 and 20.5 N X cm2 respectively and independent of sex and age. The loss of force during a 2-min stimulated fatigue test was the same in the children as the adults. The average fatigue indices ranged from 0.52 to 0.72 in the children, compared with 0.68 in the adults. It is concluded that absolute differences in muscle strength in children are a function of muscle mass. The force generating capacity expressed in N X cm2, fatiguability, contraction and relaxation times of the triceps surae would appear to remain unchanged through adolescence and early adulthood.

Adolescent↗
PubMed1983

Electrically evoked and voluntary maximal isometric tension in relation to dynamic muscle performance in elderly male subjects, aged 69 years.

The dynamic performance and electrically evoked mechanical properties of elderly triceps surae muscle have been investigated in 9 men, aged 69 yr. Dynamic performance consisted of cycling on a force bicycle and a vertical jump off two feet from a force platform. The results showed that the time to peak tension (TPT) and half relaxation time (1/2 RT) were significantly greater (p less than 0.001) by 30 ms and 22 ms and the supramaximal twitch (Pt) and tetanic (20 Hz-P020) tensions and maximal voluntary contraction (MVC) were less by 45 N (-33%), 708 N (-49%), and 899 N (-43%) in the elderly compared with young male control subjects. On the force platform, the height jumped (Ht), maximal force exerted (P), take-off velocity (VT), net impulse (NI) and peak power output (W) were less by 18.6 cm, 173 N, 0.9 ms-1, 52 Ns and 1120 w respectively. Similar differences of power, force and velocity were observed on the force bicycle. The reduction of W in the elderly was associated with the contractile characteristics of the leg muscle. The loss of contractile speed and capacity to to generate force in old people was reflected in their inability to develop power during the performance of a maximal vertical jump and cycling.

Aged↗
PubMed1983

The effect of endurance-training on the maximum activities of hexokinase, 6-phosphofructokinase, citrate synthase, and oxoglutarate dehydrogenase in red and white muscles of the rat.

Adult female rats were subjected to an eleven-week endurance-training programme, and, for the first time, the maximum activities of enzymes that can indicate the quantitative capacities of both anaerobic glycolysis and the Krebs cycle in muscle (viz. 6-phosphofructokinase and oxoglutarate dehydrogenase respectively) were measured in heart plus white and fast-oxidative skeletal muscle. No changes were observed in heart muscle. In fast-oxidative skeletal muscle, activities of hexokinase, citrate synthase, and oxoglutarate dehydrogenase were increased by 51, 26, and 33% respectively but there was no effect on 6-phosphofructokinase. These results demonstrate that in red muscle there is no effect of this training programme on the anaerobic capacity but that of the aerobic system is increased by one third. In white skeletal muscle, only the activity of citrate synthase was increased, which indicates that this activity may not provide even qualitative information about changes in capacity of the Krebs cycle.

Aerobiosis↗
PubMed1983

Effect of temperature on the contractile properties and muscle power of triceps surae in humans.

The effects of heating and cooling on the electrically evoked mechanical and contractile properties of the triceps surae in relation to the maximal dynamic performance of the leg muscles during cycling and vertical jumping have been examined in five healthy male subjects. A mean rise of 3.1 degrees C in muscle temperature (Tm) was associated with a decrease in time to peak tension (TPT) and half-relaxation time (1/2RT) but was without effect on twitch (Pto) and tetanic tension at 20 Hz (Po20) and 40 Hz (Po40) and maximal voluntary contraction (MVC). Reducing Tm by 8.4 degrees C had the opposite effect on TPT and 1/2RT and produced a fall in Pto, Po40, and MVC. The peak power output during cycling (W1) and jumping (W) was linearly related to Tm as well as negatively associated with TPT. The best single guide to W and W1 was given by a ratio of MVC to TPT: W (W) = 626.5 + 79.04 (MVC/TPT)(N/ms; r = +0.82) and W1 (W) = 1,342 + 84.9 (MVC/TPT)(N/ms; r = +0.87). The results underline the importance of the contractile and force generating capacity of human muscle in determining maximal power output and performance during exercise of a few seconds duration.

Adult↗
PubMed1983

Contractile properties of elderly human triceps surae.

Maximal electrically evoked and voluntary contractions of the triceps surae were repeatedly measured over several weeks in 13 elderly men, mean age 69.6 +/- 1.3 years. All subjects were found to be tolerant of supramaximal single twitch stimuli from the first occasion of measurement onwards and were habituated to supramaximal tetanic stimulation at frequencies of 10 and 20 Hz after three occasions of measurement. There was a significant increase in maximal voluntary contraction between the first and second occasions of measurement, but thereafter it remained unchanged. The coefficient of variation for maximal twitch and tetanic tensions and MVC were 12.5, 9.0 and 8.3%, respectively. Comparison with previously reported data showed that elderly muscle had an increased time-to-peak twitch tension development (148 +/- 15 ms) compared with young subjects (113 +/- 11 ms). The respective half relaxation times were 99 +/- 13 and 78 +/- 4 ms. Maximal tetanic tensions at frequencies of 10 and 20 Hz were significantly lower in the elderly men, 520 +/- 168 and 716 +/- 193 N respectively compared with 742 +/- 133 and 1,162 +/- 199 N respectively in the young subjects. A 2-min test involving repeated tetanisation of the triceps surae showed that though the absolute loss of tension was the same the relative loss was greater in the older than the younger men. It is concluded that muscle function in the elderly can be reliably assessed. The results suggest that the triceps surae of the elderly are weaker, more slowly contracting and show a greater relative force loss, when subjected to a standard "fatigue' test procedure, than young triceps surae.

Aged↗
PubMed1983

Effects of dynamic exercise on muscle function in elderly men, aged 70 years.

The maximal electrically evoked and voluntary contractions of the triceps surae were measured, before and after 30 min of continuous uphill walking, in 8 elderly men aged 67-71 years. The exercise was performed on a motor-driven treadmill and corresponded to 66-74% of their predicted maximal aerobic power output. During the control period, before exercise, twitch tension (Pt), time-to-peak tension (TPT) and half relaxation time (1/2RT) of the maximal twitch response were 102 +/- 29 N, 156 +/- 15 ms and 98 +/- 11 ms; the tetanic responses at frequencies of 10 Hz (PO10) and 20 Hz (PO20) and the maximal voluntary contraction (MVC) averaged 600 +/- 103, 766 +/- 106 and 1,225 +/- 185 N, respectively. The fatigue index in response to a 2-min test involving repeated tetanisation of the triceps surae was 0.40 +/- 0.14. None of these variables (except TPT which was decreased to 145 +/- 11 ms, p less than 0.001) was significantly changed following exercise. It was concluded that exercise of relatively high intensity and duration in healthy elderly men does not impair the force-generating capacity of the lower leg muscles nor increase their fatigability.

Aged↗
PubMed1983

Isometric training in human elbow flexor muscles. The effects on voluntary and electrically evoked forces.

The elbow flexor muscles of four men were trained using maximal voluntary isometric contractions. Thirty contractions a day were performed for five weeks. The four men and four control subjects were tested once a week: measurements of the supramaximally stimulated isometric twitch force, the time taken for the twitch force to peak and the tetanic force were carried out; simultaneously, measurements of the force of maximal voluntary isometric contraction and resistance to fatigue were made. The testing sessions produced no training effect on control subjects. Training produced a 20 per cent increase in the force of maximal voluntary isometric contraction after five weeks, but the forces of electrically evoked twitch and tetanus showed no increase. It was concluded that the increase in the force of maximal voluntary isometric contraction must be related to factors other than the force-generating capacity of the muscle fibres themselves.

Adult↗
PubMed1982

Contractile properties of the human triceps surae with some observations on the effects of temperature and exercise.

The contractile properties of the triceps of five healthy male subjects (mean age 22 years) during electrically stimulated and voluntary isometric muscle contractions were investigated and some observations made on the effects of muscle heating and cooling and dynamic exercise. The times to peak twitch tension (TPT) and half relaxation time (1/2RT) were 111 +/- 20 ms and 83 +/- 13 ms respectively. Heating and prior exercise decreased, and cooling severely prolonged, TPT and 1/2RT. Exercise and heating had no effect on supramaximal twitch tension (Pt0) but cooling the muscle to a temperature of 24.3 degrees C reduced it by 52%. The effects of repetitive stimuli on Pt0 were dependent on frequency; at 0.2 Hz potentiation was observed but at 2 Hz, Pt0 was depressed under control conditions. Heating had no effect on these responses but cooling reversed the 2 Hz and abolished 0.2 Hz response. Post-tetanic potentiation of the twitch was observed under all conditions of measurement. At submaximal stimulation voltages, heating and exercise enhanced twitch and tetanic tensions, but at supramaximal voltages heating reduced tetanic tension (P0) at 10 Hz (by 115 N), though not at 20 Hz. Exercise decreased P0 at both frequencies of stimulation. Cooling significantly reduced the maximal voluntary contraction and P0 at 20 Hz. At submaximal voltages, heating enhanced and cooling severely depressed tetanic tensions at high frequency (100 Hz) stimulation. A 2-min fatigue test was unaffected by heating but cooling reduced force generation at the onset of, and the decline of force during, the test. It was concluded that studies of the contractile properties of human muscle in vivo should be based on supramaximal stimulation, and that temperature and prior exercise should be carefully standardised in order to obtain reliable and meaningful results.

Adult↗