S. Garner

Comparison of two regimens of concurrent strength and endurance training.

To compare the responses to doing strength (S) training on alternate days with endurance (E) training vs doing both types of training on the same days per week, seven young men (group A-2 d) did S and E training together in single sessions 2 d.wk-1 for 20 wk. A second group (B-4 d, N = 8) did the S training on 2 d.wk-1 and E training on 2 other d.wk-1. S training was six to eight sets of 15-20 RM on a leg press weight machine. E training was six to eight 3-min bouts of cycle ergometer exercise at 90-100% VO2max. B-4 d (25%) increased leg press 1 RM more (P less than 0.05) than A-2 d (13%), but the groups increased similarly (A-2 d, B-4 d) in knee extensor (31%, 34%) and flexor (12%, 14%) cross-sectional area and vastus lateralis mean fiber area (33%, 25%). Increases in VO2max (7%, 6%), repetitions with 80% 1 RM (39%, 64%), repetitions with the pre-training 1 RM (33, 55), and PFK (19%, 10%) and LDH (15%, 23%) activity did not differ (P greater than 0.05) between groups. CS activity increased significantly only in A-2 d (26%; B-4 d, 6%). It is concluded that same day (vs different day) concurrent strength and endurance training may impede strength development without impeding hypertrophy. On the other hand, same day training may enhance increases in CS activity but not VO2max or weight lifting endurance.

The effects of strength training in patients with selected neuromuscular disorders

Five subjects with spinal muscular atrophy, limb-girdle or facioscapulohumeral muscular dystrophy, were studied. Measurements pre- and post-training included: maximum isometric, dynamic and isokinetic strength, in single-arm curl and double-leg press exercises; contractile properties of the elbow flexors; computerized tomography of the upper arms and thighs; muscle biopsies from the biceps brachii muscle of each arm in three subjects. Dynamic weight training was performed 3 times per week for 9 wk; exercises comprised unilateral arm curls (the contralateral arm acted as a control), and bilateral leg press. Strength increases in the trained arm were between 19 and 34%, and from -14 to +25% in the control arm; leg strength increased from 11 to 50%. Moreover, the pretraining maximum load could be lifted from 3 to 48 times in the trained limbs, and from 1 to 13 times in an untrained limb before fatigue. Contractile properties of the elbow flexors were unchanged with training, but pre-intervention, three subjects demonstrated incomplete motor unit activation. Most of the gains in strength were apparently due to a neural adaptation, rather than muscle hypertrophy. The tomograms and biopsy samples were inadequate to determine muscle, or muscle fiber areas with confidence; they did indicate however, no additional overt muscle structural damage. Strength training may be a potentially useful therapeutic option in the management of selected neuromuscular disorders.

Reduced voluntary electromyographic activity after fatiguing stimulation of human muscle.

1. After ischaemic ankle dorsiflexor muscles had been fatigued by repetitive stimulation of the peroneal nerve at 15 Hz, there was a reduction in voluntary EMG activity which persisted as long as the arterial cuff remained inflated. 2. The reduction in voluntary EMG activity could not have been due to loss of excitability at the neuromuscular junctions or muscle fibre membranes since the M‐waves (muscle compound action potentials) evoked by peroneal nerve stimulation were well maintained. 3. The preceding observations were consistent with the view that the reduction in EMG activity was due to reflex inhibition of motoneurones by afferents from the fatigued muscle. 4. The absence of responses to stimuli interpolated among the voluntary activity indicated that any motor units which could not be recruited in the fatigued muscle were no longer capable of generating tension.

Prolongation of twitch potentiating mechanism throughout muscle fatigue and recovery

Measurements have been made of twitch amplitudes in human ankle dorsiflexor muscles during and following fatiguing electrical stimulation. In six subjects, studied with the arterial circulation occluded, the twitch was observed to undergo an early potentiation (mean, 99 +/- 50%) followed by complete disappearance. A second, smaller phase of potentiation (mean, 25 +/- 30%) occurred during recovery and gave way to prolonged depression of the twitch. A comparison of these results with those obtained with an intact circulation suggested that the four phases in the behavior of the twitch were the net result of two processes, potentiation and fatigue, with different time courses. Provided they are timed appropriately, observations of twitch amplitude can provide useful information concerning the development of, and recovery from, muscle fatigue.