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A number of mechanisms have been proposed for the elevation in oxygen consumption following exercise. Biochemical processes that return muscle to its preexercise state do not account for all the oxygen consumed after exercise. It is possible that mechanical activity in resting muscle, which produces low frequency vibrations (i.e., muscle sounds: mechano-myographic [MMG] activity), could contribute to the excess postexercise oxygen consumption. Therefore the purpose of this study was to determine whether the resting MMG amplitude changes after exercise, and whether the change is related to the elevation in oxygen consumption (VO2). Ten young male subjects (22.9 yrs) performed 30 minutes of exercise on a cycle ergometer at an intensity corresponding to 70% peak VO2. Oxygen consumption was measured by indirect calorimetry, and MMG by an accelerometer placed over the mid-quadriceps before exercise and for 5.5 hours after exercise. MMG activity, expressed as mean absolute acceleration, was significantly elevated for the 5.5 hours of measurement after exercise (p < 0.05). MMG and VO2 decayed exponentially after exercise with time constants of 7.2 minutes and 7.4 minutes, respectively. We conclude that muscle is mechanically active following exercise and that this may contribute to an elevated VO2.

Research in animal models indicates that without estrogen, the effectiveness of exercise for increasing bone mineral in females is reduced. With decreased estrogen levels, there is an increase in the threshold at which strains are detected by bone, in turn reducing the transmission of mechanical to biochemical signals for bone formation. Studies combining estrogen replacement and exercise training in postmenopausal women have yielded mixed results but indicate that the combination of interventions may be more effective than either intervention alone for increasing bone mass. Given the continued debate over the risks and benefits of estrogen replacement, other compounds such as bisphosphonates or phytoestrogens may be preferred in combination with exercise training for optimally increasing bone mass and preventing osteoporotic fracture. Studies on animals show that the combination of bisphosphonate or phytoestrogen supplementation with exercise training is effective, but trials in humans are lacking.

The issue of whether there is a difference in the amount of force produced from a simultaneous two-limb maximal contraction compared to the sum of individual one-limb contractions has received considerable debate in the literature. A bilateral deficit (BLD) is when the resultant force from bilateral homonymous limb contractions is less than the summed force of individual limb contractions. Determining whether differences exist between one- and two-limb movements may provide insight into complex neuromuscular control patterns. Many dynamic two-limb studies report a BLD, whereas isometric studies are more numerous and controversial. It is important to categorize the movements studied in order to establish consistency. This paper purports that the BLD is an unstable phenomenon, and its presence should be considered in the context of the movement studied. Most likely, this phenomenon is dependent upon some minor deviation in descending drive between the cortical level and peripheral motor neuron

The relationship between resting thyroid hormone concentrations and exercise muscle metabolism was examined among eumenorrheic endurance-trained (n = 11), amenorrheic endurance-trained (n = 8), and eumenorrheic nonathletic (n = 13) subjects. Muscle metabolism was assessed with 31Phosphorous magnetic resonance spectroscopy by measuring changes in phosphocreatine (PCr), inorganic phosphate (Pi), and pH during plantar flexion exercise and recovery. All groups had similar Pi/PCr ratios and pH changes during exercise. Eumenorrheic endurance-trained subjects had faster recovery rates for PCr and Pi/PCr following exercise compared to the nonathletes (p < .05) and faster recovery rates for PCr compared to amenorrheic subjects (p < .05). Thyroxine (T4) and triiodothyronine (T3) levels were significantly lower in amenorrheic subjects compared to both eumenorrheic groups (p < .05). It was concluded that routine training enhances muscle metabolism, as measured by phosphate recovery kinetics. This enhancement was not evident in amenorrheic athletes with reduced T3 and T4 concentrations.

We evaluated the effect of endurance training (cycling 3 times per week for 12 weeks) on succinate dehydrogenase (SDH) activity in the subsarcolemmal (SS) and intermyofibrillar (IMF) regions of vastus lateralis muscle fibres in 7 individuals (4 females and 3 males). SDH activity of the SS region increased 9.4% and 12.8% in type I and II fibres, respectively (p < .05). SDH activity of the IMF region increased 4.7% and 6.7% in type I and II fibres, respectively (p < .05). This was less than the increase in the SS region (p < .05). No significant changes were observed in a control group (4 females and 3 males). These data suggest that mitochondria in the SS and IMF regions of human vastus lateralis muscle fibres are sensitive to endurance training. The greater response in the SS region suggests that the metabolic requirements of SS mitochondria were stressed to a greater extent than IMF mitochondria with endurance training.

The purpose of this study was to determine the influences of ageing and cardiorespiratory fitness on kinetics of VO2 during the transition to exercise of moderate intensity. Subjects performed three transitions to and from a 6-minute square wave constant load, at an intensity corresponding to 90% of ventilatory threshold (VET), to determine VO2 kinetics. The young group had a significantly faster time constant of VO2 (tau VO2). Tau VO2 was significantly correlated with VO2max for both young and old groups; however, the slope of the tau VO2--VO2max regression equation was steeper for the old group, indicating that fit older subjects had VO2 kinetics that approached those of fit young. A multiple linear regression indicated that relative fitness was the strongest significant predictor of tau VO2, followed by sex and age. Although VO2 kinetics are definitely slowed with age, relative levels of cardiorespiratory fitness also have a great influence on the dynamic response of VO2.

Thirty young women comprised three groups (n = 10 in each): whole routine (W) training, split routine training (S), and control. The W group did four upper (five sets, 6-10 RM) and three lower body (five sets, 10-12 RM) weight training exercises together in single sessions twice a week for 20 weeks. The S group did the upper body exercises 2 days a week and the lower body exercises on 2 other days of the week. The single maximal weight lift (1-RM) increased (p < 0.05) (W/S) 54/69%, 33/32%, and 21/22% in arm curl, bench press, and leg press exercises, as did arm (10/9%), and trunk (3.4/2.7%) lean tissue mass, as measured by dual energy x-ray absorptiometry. Leg lean mass increased significantly only in W (4.9% vs. 1.7% in S). Whole-body lean tissue mass increased (4.1/2.6%), and whole body % fat (-1.1/-1.3%) decreased with training. It is concluded that in healthy young women, whole and split weight training routines produce similar results over the first 5 months of training.