Resistance exercise can effectively result in an increase in muscle mass, or hypertrophy, which generally becomes apparent after several weeks of training. Muscle hypertrophy requires muscle protein synthesis to exceed protein breakdown during an extended time period. It has been firmly established that the interaction between exercise and nutrition (i.e., protein intake) is necessary to attain net protein accretion in skeletal muscle. The stimulation of protein synthesis is caused in part by stimulation of mRNA translation initiation. There is relatively little information on the response of intracellular signaling controlling mRNA translation to exercise and nutrition, especially in humans, but the available data in humans seem to suggest that a single bout of resistance exercise does not substantially enhance PI-3 kinase/mTOR signaling during the first 2 h after exercise. Moreover, it is demonstrated that the ingestion of protein or amino acids after exercise is crucial to further stimulate molecular signaling that controls translation initiation. The aim of this review is to provide an overview of the intracellular signaling related to translational control and to provide a summary of the current knowledge about the response of the signaling pathways controlling the anabolic response to exercise and nutrient intake in vivo in humans.
Michael Sagiv, Amira Sagiv, David Ben-Sira, Jacob Rudoy and Michael Soudry
Hemodynamic and left ventricular systolic function were studied by Doppler echocardiography in 14 young and 15 older adult hypertensive patients and in 15 young and 12 older normotensive individuals. Measures were made at rest and during upright deadlift isometric exercise, at 30% of maximum voluntary contraction for 3 min. At rest, young and older hypertensive patients demonstrated impaired left ventricular systolic function compared to both old and young normotensive subjects. The impaired systolic function was associated with less augmentation in systolic indices during exercise compared with resting values in young and elderly hypertensive patients, and to a lesser degree in the normotensive elderly when compared with young normotensives. These data indicate that at rest, left ventricular systolic function may be compromised in hypertensive patients with left ventricular hypertrophy and, to a lesser extent, in the normotensive elderly. However, other factors in chronic hypertension may contribute to abnormal systolic function and override the effects of aging alone.
Gary E. Morin, David Tiberio and Gary Austin
A characteristic of scapulothoracic dysfunction is the tendency for the upper regions of the trapezius to hypertrophy in relation to its middle and lower portions. This creates a muscular imbalance that can alter scapular position and subsequently the length–tension relationship of the shoulder muscles. Tape was applied over the right upper trapezius to inhibit electrical activity in the muscles of 10 uninjured subjects. EMG activity was recorded in two locations of the upper trapezius and one location in the middle to lower trapezius region while each subject maintained an isometric contraction designed to activate both muscles. With the tape applied, there was a statistically significant reduction in EMG activity of the upper trapezius with a corresponding increase in the middle/lower trapezius. The ability of the tape to alter trapezius activity in this fashion may help correct muscular imbalances in the trapezius muscle.
Eiji Yamada, Takashi Kusaka, Satoshi Tanaka, Satoshi Mori, Hiromichi Norimatsu and Susumu Itoh
To investigate changes in motor-unit activity and muscle oxygenation (MO) during isometric contraction with and without vascular occlusion using surface electromyography (EMG) and near-infrared spectroscopy.
Design and Setting:
MO and EMG of the right vastus medialis muscle were measured during isometric contraction at 30%, 50%, and 70% maximal voluntary contraction (MVC), with and without vascular occlusion.
6 healthy men.
Integrated EMG (IEMG) and mean power frequency were significantly higher with vascular occlusion at 30% and 50% MVC. MO reduction at each load was significantly lower with vascular occlusion. A significant positive correlation was found between IEMG and changes in MO level under both conditions.
These results suggest that oxygen supply to active muscles was impaired by occlusion and that type II fibers were then preferentially recruited, which suggests that hypertrophy occurs in low-intensity exercise in patients with limitations resulting from advanced age, pain, or postsurgery limitation.
Roy J. Shephard
Attention is drawn to specific practical and ethical concerns that may arise when researchers study responses to vigorous exercise in populations with disabilities. It is argued that the study of such individuals can provide important information regarding responses to exercise by nondisabled people. This thesis is illustrated by selected examples relating to (a) central versus peripheral limitation of oxygen transport, (b) the contribution of muscle pumping to venous return during vigorous exercise, (c) the contribution of sympathetic innervation to aerobic training responses, (d) the ceiling of muscle fiber hypertrophy, (e) the functional demands of daily living, and (f) the responsiveness of young children to aerobic training. It is concluded that exercise physiologists have already learned much about normal reactions to exercise by studies involving those disabilities, but there remains scope for many further investigations exploiting the special characteristics of such populations.
Kathleen F. Janz, Smita Rao, Hope J. Baumann and Jaime L. Schultz
Ground reaction forces (GRF) are associated with bone hypertrophy; therefore, they are important to understanding physical activity’s role in children’s bone health. In this study, we examined the ability of accelerometry to predict vertical GRF in 40 children (mean age 8.6 yr) during slow walking, brisk walking, running, and jumping. Correlation coefficients between accelerometry-derived movement counts and GRF were moderate to high and significant during walking and running, but not during jumping. Given a large proportion of children’s daily physical activity involves ambulation, accelerometry should be useful as a research method in bone-related research. However, this method underestimates GRF during jumping, an important physical activity for bone modeling and remodeling.
Recognizing the cardiac features of athletically trained children bears importance for health care providers and exercise physiologists alike. This literature review reveals that ventricular enlargement and/or hypertrophy are commonly observed in studies of pre- and early-adolescent endurance athletes, yet the magnitude of these features is less than that described in adult athletes. Moreover, the upper range of values in child athletes is sufficiently small that clinical confusion with findings mimicking those in individuals with heart disease should not be expected to occur. In contrast to sex differences in the “athlete’s heart” in adults, cardiac structural findings in child athletes are similar in males and females. The extent that cardiac features observed in trained child athletes reflect a response to training or are influenced by genetic preselection remains uncertain.
Luke R. Bucci, James F. Hickson Jr., Ira Wolinsky and James M. Pivarnik
Ornithine supplementation has gained popularity with athletes because of its alleged potential to release anabolic hormones, factors governing skeletal muscle hypertrophy. Three female and nine male bodybuilders sewed as subjects in a study to test the effectiveness of oral ornithine in bringing about the release of insulin, an anabolic hormone. After an overnight fast, subjects were administered 40, 100, or 170 mg·kg−1 L-ornithine.HC1 by mouth in a random fashion on three consecutive Saturday mornings. Blood samples were drawn at baseline (T=O), 45, and 90 min afterward. Serum ornithine levels were elevated (p~0.01) at T=45 and 90 min for all three dosage levels. However, serum insulin did not change from baseline levels at any dose of ornithine. The present findings show that ornithine is not an insulin secretagogue.
Gary B. Wilkerson and Arthur J. Nitz
Ankle proprioception is widely regarded as an important factor that affects susceptibility to ankle sprain, but the precise mechanisms by which proprioceptive abilities may enhance ankle stability are not well understood. Pertinent literature is reviewed and theoretical interrelationships among factors that may affect dynamic ankle function are discussed. Topics addressed include mechanoreceptor function, muscle spindle function, postural balance, ankle edema, joint capsule distension, synovial hypertrophy, capsuloligamentous laxity, anterolateral rotary instability, ankle giving way, reflexive muscle splinting, articular deafferentation, neurogenic inflammation, muscular de-efferentation, and enhancement of compensatory neuromuscular mechanisms. Recommendations for future research are presented in the form of questions that cannot be adequately answered at present concerning the role of proprioceptively mediated mechanisms in the maintenance of dynamic ankle stability.
Vasilios I. Kalapotharakos, Maria Michalopoulou, George Godolias, Savvas P. Tokmakidis, Paraskevi V. Malliou and Vasilios Gourgoulis
The purpose of this study was to investigate the effects of a 12-week resistance-training program on muscle strength and mass in older adults. Thirty-three inactive participants (60–74 years old) were assigned to 1 of 3 groups: high-resistance training (HT), moderate-resistance training (MT), and control. After the training period, both HT and MT significantly increased 1-RM body strength, the peak torque of knee extensors and flexors, and the midthigh cross-sectional area of the total muscle. In addition, both HT and MT significantly decreased the abdominal circumference. HT was more effective in increasing 1-RM strength, muscle mass, and peak knee-flexor torque than was MT. These data suggest that muscle strength and mass can be improved in the elderly with both high- and moderate-intensity resistance training, but high-resistance training can lead to greater strength gains and hypertrophy than can moderate-resistance training.