We investigated the reproducibility of measurements of maximal voluntary torque and maximal voluntary activation using twitch interpolation. On 5 days, each of 5 subjects performed 10 maximal voluntary isometric contractions of their elbow flexors. Single supramaximal stimuli were delivered over biceps brachii at the measured peak torque during each effort, and in the relaxed muscle 5 s later. A voluntary activation score was calculated from the size of twitches evoked by the stimuli (resolution < 0.15 Nm). Although all subjects were able to drive the stimulated elbow flexor muscles maximally in some trials, they did not do so in 75% of all contractions. Maximal voluntary torques did not vary significantly within a subject between sessions. There were consistent differences in the level of maximal voluntary activation between subjects (P < 0.01), but no differences in voluntary activation within an individual across days in 4 of 5 subjects. Failure to drive the stimulated elbow flexor muscles maximally was not associated with inadvertent co-contraction of the antagonist muscles.

Background and objective: Telerehabilitation has the potential to increase access to pulmonary rehabilitation (PR) for patients with COPD who have difficulty accessing centre-based PR due to poor mobility, lack of transport and cost of travel. We aimed to determine the effect of supervised, home-based, real-time videoconferencing telerehabilitation on exercise capacity, self-efficacy, health-related quality of life (HRQoL) and physical activity in patients with COPD compared with usual care without exercise training. Methods: Patients with COPD were randomized to either a supervised home-based telerehabilitation group (TG) that received exercise training three times a week for 8 weeks or a control group (CG) that received usual care without exercise training. Outcomes were measured at baseline and following the intervention. Results: Thirty-six out of 37 participants (mean AE SD age = 74 AE 8 years, forced expiratory volume in 1 s (FEV 1 ) = 64 AE 21% predicted) completed the study. Compared with the CG, the TG showed a statistically significant increase in endurance shuttle walk test time (mean difference = 340 s (95% CI: 153-526, P < 0.001)), an increase in self-efficacy (mean difference = 8 points (95% CI: 2-14, P < 0.007)), a trend towards a statistically significant increase in the Chronic Respiratory Disease Questionnaire total score (mean difference = 8 points (95% CI: −1 to 16, P = 0.07)) and no difference in physical activity (mean difference = 475 steps per day (95% CI: −200 to 1151, P = 0.16)). Conclusion: This study showed that telerehabilitation improved endurance exercise capacity and self-efficacy in patients with COPD when compared with usual care.

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The response of the diaphragm to the postural perturbation produced by rapid flexion of the shoulder to a visual stimulus was evaluated in standing subjects. Gastric, oesophageal and transdiaphragmatic pressures were measured together with intramuscular and oesophageal recordings of electromyographic activity (EMG) in the diaphragm. To assess the mechanics of contraction of the diaphragm, dynamic changes in the length of the diaphragm were measured with ultrasonography. With rapid flexion of the shoulder in response to a visual stimulus, EMG activity in the costal and crural diaphragm occurred about 20 ms prior to the onset of deltoid EMG. This anticipatory contraction occurred irrespective of the phase of respiration in which arm movement began. The onset of diaphragm EMG coincided with that of transverses abdominis. Gastric and transdiaphragmatic pressures increased in association with the rapid arm flexion by 13.8 ± 1.9 (mean ±s.e.m.) and 13.5 ± 1.8 cmH2O, respectively. The increases occurred 49 ± 4 ms after the onset of diaphragm EMG, but preceded the onset of movement of the limb by 63 ± 7 ms. Ultrasonographic measurements revealed that the costal diaphragm shortened and then lengthened progressively during the increase in transdiaphragmatic pressure. This study provides definitive evidence that the human diaphragm is involved in the control of postural stability during sudden voluntary movement of the limbs.

SUMMARY1. To determine whether discomfort associated with breathing (dyspnoea) is related to the chemical drive to breath, three subjects were totally paralysed while fully conscious. Subjective responses to a rising C02 stimulus were obtained during rebreathing, rebreathing with C02 added, and breath holding. Dyspnoea was measured with a 10-point Borg scale.2. Following nasotracheal intubation and ventilation (oxygen saturation, 02,Sat' 98-100°% and end-tidal C02, PET,CO,, 30-40 mmHg), total neuromuscular blockade was induced by a rapid injection of atracurium (>2'5 mg kg1) and complete paralysis was maintained with an infusion (5 mg (kg h)-'). Paralysis was confirmed by abolition of the compound muscle action potentials of both the diaphragm and abductor hallucis evoked by supramaximal electrical stimulation of the relevant nerves. Communication via finger movement was preserved for the first 20-30 min following paralysis by inflation of a sphygmomanometer cuff on one arm.3. Before and during complete paralysis, dyspnoea increased progressively during hypercapnia produced by rebreathing (with or without C02 added to the circuit at 250 ml min-'). The mean PET,CO, eliciting 'severe' dyspnoea was 46 mmHg during rebreathing, 42 mmHg during 'breath holding', and 52 mmHg during rebreathing with added C02. There were no significant differences between the values obtained during paralysis and in the control study immediately before paralysis. S. C. GANDEVIA AND OTHERS evokes, can lead to discomfort in the absence of any contraction of respiratory muscles. 5. During paralysis, attempted contraction of arm, leg and trunk muscles increased heart rate and blood pressure. For attempted handgrip contractions, the increases in heart rate (range, 7-15 beats min-') and mean arterial pressure (range, 20-32 mmHg) were similar to those recorded with actual contractions in trials immediately before paralysis. In one subject, graded increases in heart rate and blood pressure occurred for attempted contractions of 45 s duration over a range of intensities (0-100% maximal effort).6. During complete paralysis, transcranial electromagnetic stimulation of the motor cortex produced illusory twitch-like movements of the wrist and digits. This also occurred in separate studies during complete ischaemic paralysis and anaesthesia of the forearm and hand. These illusory movements thus reflect activation of intracerebral structures by the induced currents. No sensation of effort accompanied the transcranial stimuli delivered during whole-body paralysis.7. Attempted voluntary movement of a limb paralysed with intravenous atracurium was accompanied by a marked sense of effort, but it also produced definite illusions of movement. The limb appeared to move slowly in the opposite direction to that desired. However, in separate studies, these illusions were absent when all large diameter axons in the arm were blocked by ischaemia. This suggests that the illusory limb movements were due to incomplete neuromuscular block of the intrafusal endplates.

The ability to activate human motoneurons supplying individual intrinsic muscles of the hand was examined during acute deafferentation of the muscles. Tungsten microelectrodes were inserted percutaneously into motor fascicles of the ulnar nerve of 5 subjects, which was then blocked distally with local anaesthetic. In 4 subjects unitary action potentials were recorded from 16 motor axons, which were identified with respect to their target muscles. In the complete absence of muscle afferent feedback, subjects could voluntarily recruit motoneurons, grade their discharge and sustain a constant level of activity. Significant facilitation of motor efforts was provided by cutaneous feedback from the digits via the median nerve. During attempted maximal voluntary efforts the mean discharge frequencies of single motor axons were significantly lower than those of normally-innervated motor units. This finding suggests that peripheral afferents have a net facilitatory influence on motoneurons. However, during prolonged (20-30 s) maximal voluntary efforts the deafferented motoneurons did not display the progressive decline in discharge frequency shown by normally-innervated motor units during contractile fatigue, a finding consistent with two possible explanations: disfacilitation or reflex inhibition of the motoneuron pool by peripheral afferents. The results also indicate that the otherwise intact nervous system can perform some simple motor tasks with no proprioceptive input other than knowledge of the motor commands. Other factors may contribute to the poor motor performance reported for patients with severe sensory deficits.

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SUMMARY1. Human muscle endurance is apparently enhanced during maximal voluntary contractions at short muscle lengths (McKenzie & Gandevia, 1987) but the ability of subjects to activate muscles fully at short lengths has not been established. Therefore this study examined the voluntary capacity to activate muscles fully at control (near resting) lengths and at decreased muscle lengths. Changes in mechanical properties of twitch responses to electrical stimulation of relaxed muscles at short muscle lengths were also documented. The abductor digiti minimi, elbow flexors and tibialis anterior were studied in five subjects.2. For the three muscle groups, the mean reduction in twitch force between the control and short muscle lengths ranged from 46-51 %. At the short length there was a 9-13 % reduction in the contraction time and a 21-27 % reduction in the halfrelaxation time. Maximal voluntary force declined by 21-49 % at the short muscle length. A reduction in muscle length produced a shift to the right of the force-frequency curve as determined by brief trains of electrical stimuli.3. During maximal efforts single or brief trains of two to four supramaximal stimuli, delivered to the parent nerve or motor point, failed to increase the force at a latency appropriate for onset of a muscle twitch in some but not all attempts. Each subject achieved 'maximal activation' of the muscle in a similar proportion of attempts at the control and short muscle lengths.4. These results suggest that maximal voluntary activation of motoneurone pools is possible at short muscle lengths and that the central nervous system is able to maintain the discharge of motoneurones close to 'fusion' frequency despite a decrease in the temporal characteristics of the isometric twitch.