Biomedical subjects

J M Saxton

Publications and source records attributed to J M Saxton.

5 recordsLinked to original sources

PubMed1996

Changes in human skeletal muscle contractile function following stimulated eccentric exercise.

Indices of human skeletal muscle contractile function were examined in nine subjects for up to 9 days following a single bout of stimulated eccentric exercise. Eccentric muscle actions of the knee extensor muscles were evoked by percutaneous electrical myostimulation (PES). Delayed onset muscle soreness (DOMS), elevated serum creatine kinase activity, chronic force loss, and a decline in the 20:100 Hz force ratio were observed in the days postexercise. The exercised knee extensor muscles demonstrated an impaired ability to respond to PES. This was evident by an increased time delay between the start of 100 Hz PES and the onset of contraction immediately postexercise [22.3 (SD 15.9)%, P < 0.01] and 3 days postexercise [14.9 (SD 18.1)%, P < 0.05]. Muscle relaxation rates appeared unaffected by the eccentric exercise protocol, where the muscles showed no differences in the time between the end of PES and the onset of relaxation (P > 0.05). During the days following the exercise, no significant differences were observed in the time between the start of contraction and attainment of 70% of the mean tetanic force following a single 1-s pulse of PES. Similarly, no significant differences were observed in the time between the start of relaxation and attainment of 70% of the total relaxation during the same time. The increased delay in excitation-contraction coupling observed immediately postexercise and 3 days after the exercise, may reflect a damage-induced delay in action potential propagation. Muscle relaxation rates postexercise remained unchanged, which would seem to indicate normal functioning of the sarcoplasmic reticulum, suggesting this was not the site of failure in excitation-contraction coupling.

Adult↗

PubMed1996

Length-specific impairment of skeletal muscle contractile function after eccentric muscle actions in man.

1. The effects of maximum voluntary eccentric muscle actions on forearm flexor strength were studied at three different elbow joint angles (0.87, 1.57 and 2.79 rad) to examine whether subsequent impairment of contractile function is muscle length-specific. 2. A bout of 70 maximum voluntary eccentric muscle actions performed with the forearm flexors elicited delayed muscle soreness, efflux of creatine kinase into the blood, loss of elbow joint range of motion and a prolonged decline in maximum voluntary isometric contraction torque at the three elbow angles monitored (P < 0.01) in 30 subjects. 3. The relative decline in maximum voluntary isometric contraction torque after eccentric exercise differed between elbow angles (P < 0.01). The greatest decline in strength relative to baseline was observed at the most acute elbow angle of 0.87 rad, followed by 1.57 and 2.79 rad respectively. Superimposed electrical stimulation in a subgroup of eight subjects did not increase the torque elicited by the forearm flexors during maximum voluntary contraction tests at the most acute elbow angle (0.87 rad) at any time-point after eccentric exercise, suggesting the disproportionate loss of strength at short muscle length was not due to the inhibitory effects of muscle soreness. 4. Measures of arm circumference and ability to fully flex the elbow (in the same subgroup of eight subjects) suggested the greater decline in strength at the acute elbow angle was not due to the possible confounding influences of muscle swelling and/or impaired muscle shortening ability on strength measurements at short muscle length. 5. These data suggest a shift in the forearm flexor length-tension relationship could account for the disparate decline in strength between elbow angles after eccentric exercise. The disproportionate loss of strength at short muscle length suggests that eccentric exercise evoked a subtle increase in muscle length, perhaps attributable to the cumulative effects of regions of lengthened sarcomeres and/or series elastic elements.

Adolescent↗

PubMed1995

Light concentric exercise during recovery from exercise-induced muscle damage.

Eight male volunteers performed two eccentric exercise bouts using the forearm flexors of first one arm, then the other. The two bouts, consisting of 70 maximum voluntary muscle actions, were separated by a period of three weeks. In the experimental condition of the study, five sets of 10 sub-maximal concentric muscle actions were performed on the four days after the eccentric bout. In the control condition of the study, no concentric work was performed. Repeated measures analysis of variance indicated an increase in serum creatine kinase activity (p < 0.01) and decreases in relaxed elbow angle (p < 0.05) and maximum voluntary contraction force (p < 0.01) at three elbow angles (0.87, 1.57 and 2.79 rad) after both eccentric bouts. However, the serum creatine kinase response to eccentric exercise was reduced in the experimental condition (p < 0.05) and recovery of maximum voluntary force production at the most acute joint angle (0.87 rad) was accelerated (p < 0.01). Although muscle soreness increased after both eccentric bouts (p < 0.05; Wilcoxon test), further concentric exercise evoked temporary relief of muscle soreness two days after the bout (p < 0.05; Wilcoxon test). However, light concentric work had no effect on the other parameters monitored. In practical terms, these results suggest that the therapeutic effects of light concentric work on correlates of exercise-induced muscle damage are minimal.

Acceleration↗

PubMed1995

Neuromuscular dysfunction following eccentric exercise.

This study examined the effects of exercise-induced muscle damage on tremor and proprioception components of neuromuscular function. Six male and six female volunteers (aged 18-30 yr) performed 50 maximal eccentric muscle actions using the forearm flexors of the nondominant arm. Forearm flexor tremor and perception of voluntary force and joint position were monitored to assess changes in neuromuscular function. Data were analyzed using REANOVA. Serum creatine kinase activity increased from a baseline value of 68 +/- 13 IU.l-1 to 2849 +/- 852 IU.l-1 5 d after exercise (P < 0.05). This was accompanied by prolonged impaired joint range of motion (P < 0.01) and reduced maximum strength (P < 0.01). Muscle soreness peaked 3 d postexercise (P < 0.01; Wilcoxon test). Tremor amplitude was increased (P < 0.01) until 48 h after exercise, whereas the power frequency spectrum was unaffected. Perception of joint position at elbow angles of 1.57 rad (P < 0.01) and 2.09 rad (P < 0.05) and perception of force (P < 0.01) were significantly impaired when the control arm acted as the reference. Joint positions were more accurately reproduced when the experimental arm acted as its own reference. The increase in tremor amplitude and loss of proprioceptive function in the days after damage-inducing eccentric exercise suggest significant impairment of neuromuscular function.

Adolescent↗

PubMed1994

Indices of free-radical-mediated damage following maximum voluntary eccentric and concentric muscular work.

This study monitored plasma and skeletal muscle markers of free-radical-mediated damage following maximum eccentric and concentric exercise, to examine the potential role of free radicals in exercise-induced muscle damage. Fourteen male volunteers performed either (1) a bout of 70 maximum eccentric and a bout of 70 maximum concentric muscle actions of the forearm flexors (the bouts being separated by 4 weeks; n = 8) or (2) a bout of 80 maximum eccentric and a bout of 80 maximum concentric muscle actions of the knee extensors (the bouts being separated by 1 week; n = 6). Plasma markers of lipid peroxidation, thiobarbituric acid-reactive substances (TBARS) and diene-conjugated compounds (DCC) were monitored in the arm protocol and skeletal muscle markers of oxidative lipid and protein damage, malondialdehyde (MDA) and protein carbonyl derivatives (PCD) respectively, were monitored in the leg protocol. In both protocols, the contralateral limb was used for the second bout and the order of the bouts was randomised between limbs. Repeated measures ANOVA indicated significant changes from baseline following eccentric arm work on the measures of serum creatine kinase activity (P < 0.05), maximum voluntary torque production (P < 0.01) and relaxed arm angle (P < 0.01). Subjective muscle soreness peaked 2 days after eccentric arm work (P < 0.05, Wilcoxon test). However, there were no changes in the plasma levels of TBARS or DCC following the eccentric or concentric arm exercise. Immediately after concentric leg exercise, skeletal muscle PCD concentrations was significantly higher than that observed immediately after eccentric work (P < 0.05)(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗