Effect of resistance training on muscle use during exercise

Abstract

This study examined the effect of resistance training on exercise-induced contrast shift in magnetic resonance (MR) images. It was hypothesized that a given load could be lifted after training with less muscle showing contrast shift, thereby suggesting less muscle was used to perform the exercise. Nine males trained the left quadriceps femoris (QF) muscle 2 days/wk for 9 wk using 3-6 sets of 12 knee extensions each day. The right QF served as a "control." Exercise-induced contrast shifts in MR images evoked by each of three bouts of exercise (5 sets of 10 knee extensions with a load equal to 50, 75, and 100% of the maximum pretraining load that could be lifted for 5 sets of 10 repetitions) were quantified pre- and posttraining. MR image contrast shift was quantified by determining QF cross-sectional area (CSA) showing increased spin-spin relaxation time. One repetition maximum increased 14% in the left trained QF and 7% in the right untrained QF. Left QF CSA increased 5%, with no change in right QF CSA. Left QF CSA showing contrast shift was less after each bout of the exercise test posttraining. This was also true, to a lesser extent, for the right QF at the higher two loads. The results suggest that short-term resistance training reduces MR image contrast shift evoked by a given effort, thereby reflecting the use of less muscle to lift the load. Because this response was evident in both trained and contralateral untrained muscle, neural factors are suggested to be responsible.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Direct Supervision of a Strength Coach on Measures of Muscular Strength and Power in Young Rugby League Players

“…For example, Mazzetti et al (19) reported that direct supervision by personal trainers resulted in accelerated progression in training loads during 12 weeks of linear periodized resistance training in 10 men experienced in resistance training. These investigators suggested that the increased tolerance of heavy training loads leads to the stimulation of higher threshold motor units (27). Therefore, we suggest that both the observed increase in training frequency and the previously reported increase in training intensity (19) are the factors that led to the improvement in muscle strength with direct supervision in this study.…”

Skeletal muscle atrophy and increased intramuscular fat after incomplete spinal cord injury

“…In addition, previous studies showed that effective resistance training to increase muscle strength and size would last approximately 3 months. 18,26 In complete SCI, 3 months of evoked resistance training result in skeletal muscle hypertrophy up to 40%. 18 Absence of effective intervention within this period may result in the clinical consequences demonstrated in this study.…”

Vastus lateralis fatigue alters recruitment of musculus quadriceps femoris in humans

“…The KEE was performed at the MRI facility to permit image collection immediately after exercise (1,2,6,7,14,21,(33)(34)(35). Subjects performed four sets of 10 repetitions of concentric (extension phase)-eccentric (flexion phase) contractions with a load equal to 50% of the 4 ϫ 10 RM with the use of a plate-loaded knee extension machine (Badger-Magnum, Milwaukee, WI).…”

“…Standard spin-echo MR images of the left thigh were taken using a 1.5-T super-conducting magnet (Signa, General Electric, Milwaukee, WI) essentially as done previously (1,2,6,7,14,21,(33)(34)(35). Thirteen 10-mm-thick transaxial images (repetition time ϭ 1,500 ms; echo time ϭ 30 and 60 ms) of the left thigh spaced 10 mm apart were collected using 1.0 number of excitations with a whole body coil.…”

“…Whereas magnetic resonance (MR) imaging (MRI) has been used to acquire anatomical information (4,5,22), use of human skeletal muscle has also been assessed with exercise-induced contrast shift in transverse relaxation time (T2) of MR images (1-3, 6, 7, 14, 21, 33-35, 42). It has been demonstrated that this contrast shift is correlated with integrated EMG activity (1), related to isometric torque induced by electromyostimulation (EMS) (2), increases with exercise intensity (1,2,21,26,30,33,36) and the metabolic state of skeletal muscle (37,40,42), and can discriminate use among relatively small synergistic muscles (13,14) and neuromuscular compartments (3). Thus exerciseinduced contrast shift in MR images seemed ideal to assess neuromuscular plasticity among synergists.…”