Effects of acute isometric resistance exercise on cervicomedullary motor evoked potentials.

Cervicomedullary motor evoked potentials (CMEPs) in relaxed biceps brachii have been reported to facilitate after acute isometric exercise of the elbow flexors. This facilitation, which reflects either enhanced corticospinal transmission or increased motoneurone excitability, has only been documented in the limb posture used during exercise. In Experiment 1, we tested if these spinal changes "transfer" to a second posture. Fourteen individuals completed 12 sets of high-force isometric contractions of the elbow flexors with the forearm pronated. Before and after exercise, biceps CMEPs were acquired with the forearm either pronated or supinated. CMEPs in pronation and supination were facilitated after exercise, indicating transfer (57.5 ± 55.5% and 53.9 ± 54.9%, respectively; mean ± SD). In Experiment 2, we examined if exercise posture influences the effect that exercise has on CMEPs. A different sample of 14 individuals performed isometric exercise in 2 sessions. In one, exercise was performed in supination. In the other, exercise was performed in pronation. Exercise intensity and volume were the same as in Experiment 1, as were participant characteristics. CMEPs were unchanged after exercise in supination (13.6 ± 31.2%) and pronation (7.7 ± 41.5%). The absence of an effect differs from the finding of Experiment 1. Thus, effects of acute isometric resistance exercise on corticospinal transmission and/or motoneurone excitability are not as consistent as previously thought. When exercise induces this spinal change, the effect is not specific to the posture used for exercise. However, the change does not always occur, and the reasons for this remain unknown.

Acute resistance exercise and pressure pain sensitivity in knee osteoarthritis: a randomised crossover trial.

OBJECTIVE: To determine whether a single bout of resistance exercise produces an analgesic effect in individuals with knee osteoarthritis (OA). DESIGN: Eleven participants with knee OA (65.9 ± 10.4 yrs), and 11 old (61.3 ± 8.2 yrs) and 11 young (25.0 ± 4.9 yrs) healthy adults performed separate bouts of upper and lower body resistance exercise. Baseline and post-exercise pressure pain thresholds were measured at eight sites across the body and pressure pain tolerance was measured at the knee. RESULTS: Pressure pain thresholds increased following exercise for all three groups, indicating reduced pain sensitivity. For the young and old healthy groups this exercise-induced analgesia (EIA) occurred following upper or lower body resistance exercise. In contrast, only upper body exercise significantly raised pain thresholds in the knee OA group, with variable non-significant effects following lower body exercise. Pressure pain tolerance was unchanged in all groups following either upper or lower body exercise. CONCLUSION: An acute bout of upper or lower body exercise evoked a systemic decrease in pain sensitivity in healthy individuals irrespective of age. The decreased pain sensitivity following resistance exercise can be attributed to changes in pain thresholds, not pain tolerance. While individuals with knee OA experienced EIA, a systemic decrease in pain sensitivity was only evident following upper body exercise.

Spontaneous transitions in the coordination of a whole body task.

This paper describes an example of spontaneous transitions between qualitatively different coordination patterns during a cyclic lifting and lowering task. Eleven participants performed 12 trials of repetitive lifting and lowering in a ramp protocol in which the height of the lower shelf was raised or lowered 1 cm per cycle between 10 and 50 cm. Two distinct patterns of coordination were evident: a squat technique in which moderate range of hip, knee and ankle movement was utilised and ankle plantar-flexion occurred simultaneously with knee and hip extension; and a stoop technique in which the range of knee movement was reduced and knee and hip extension was accompanied by simultaneous ankle dorsi-flexion. Abrupt transitions from stoop to squat techniques were observed during descending trials, and from squat to stoop during ascending trials. Indications of hysteresis was observed in that transitions were more frequently observed during descending trials, and the average shelf height at the transition was 5 cm higher during ascending trials. The transitions may be a consequence of a trade-off between the biomechanical advantages of each technique and the influence of the lift height on this trade-off.

Concurrent strength and endurance training. A review.

Concurrent strength and endurance training appears to inhibit strength development when compared with strength training alone. Our understanding of the nature of this inhibition and the mechanisms responsible for it is limited at present. This is due to the difficulties associated with comparing results of studies which differ markedly in a number of design factors, including the mode, frequency, duration and intensity of training, training history of participants, scheduling of training sessions and dependent variable selection. Despite these difficulties, both chronic and acute hypotheses have been proposed to explain the phenomenon of strength inhibition during concurrent training. The chronic hypothesis contends that skeletal muscle cannot adapt metabolically or morphologically to both strength and endurance training simultaneously. This is because many adaptations at the muscle level observed in response to strength training are different from those observed after endurance training. The observation that changes in muscle fibre type and size after concurrent training are different from those observed after strength training provide some support for the chronic hypothesis. The acute hypothesis contends that residual fatigue from the endurance component of concurrent training compromises the ability to develop tension during the strength element of concurrent training. It is proposed that repeated acute reductions in the quality of strength training sessions then lead to a reduction in strength development over time. Peripheral fatigue factors such as muscle damage and glycogen depletion have been implicated as possible fatigue mechanisms associated with the acute hypothesis. Further systematic research is necessary to quantify the inhibitory effects of concurrent training on strength development and to identify different training approaches that may overcome any negative effects of concurrent training.

Relaxation of bovine coronary artery and activation of coronary arterial guanylate cyclase by nitric oxide, nitroprusside and a carcinogenic nitrosoamine.

The principal objective of this study was to test the hypothesis that nitroprusside relaxes vascular smooth muscle via the reactive intermediate, nitric oxide (NO), and that the biologic action of NO is associated with the activation of guanylate cyclase. Nitroprusside, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and NO elicit concentration-dependent relaxation of precontraced helical strips of bovine coronary artery. Nitroprusside, MNNG and NO also markedly activate soluble guanylate cyclase from bovine coronary arterial smooth muscle and, thereby, stimulate the formation of cyclic GMP. Three heme proteins, hemoglobin, methemoglobin and myoglobin, and the oxidant, methylene blue, abolish the coronary arterial relaxation elicited by NO. Similarly, these heme proteins, methylene blue and another oxidant, ferricyanide, markedly inhibit the activation of coronary arterial guanylate cyclase by NO, nitroprusside and MNNG. The following findings support the view that certain nitroso-containing compounds liberate NO in tissue:heme proteins, which cannot permeate cells, inhibit coronary arterial relaxation elicited by NO, but not by nitroprusside or MNNG; the vital stain, methylene blue, inhibits relaxation by NO, nitroprusside and MNNG; heme proteins and oxidants inhibit guanylate cyclase activation by NO, nitroprusside and MNNG in cell-free mixtures. The findings that inhibitors of NO-induced relaxation of coronary artery also inhibit coronary arterial guanylate cyclase activation suggest that cyclic GMP formation may be associated with coronary arterial smooth muscle relaxation.