No abstract

Changes in muscle fibers of adolescent Thoroughbreds are caused by training and not by growth. The most noticeable change was for the SDH activity of type-IIX/B fibers. These changes in the gluteus medius muscle of adolescent Thoroughbreds were considered to be appropriate adaptations to running middle distances at high speeds.

Hybrid fibers have an important role for determining the proportion of muscle fiber type in horses < 24 months old, and the metabolic and anatomic properties of the hybrid fibers are well coordinated, as in mature horses.

No abstract

Age-related changes of physiological and biochemical properties were examined in the diaphragm muscle, which has particularly high activation compared to that of other skeletal muscles. The diaphragm from 10-week-, 50-week-and 100-week-old male Wistar rats were used to measure in vitro isometric contractile properties, sarcoplasmic reticulum (SR) Ca 2+ -ATPase activity, and myosin heavy chain (MHC) isoform composition. Although there were no significant differences in specific twitch tension of the diaphragm among the groups, there was significant reduction in specific tetanic tension in the 50-week to 100-week groups. The contraction time and 1/2 relaxation time of twitch contraction extended with aging, and significant differences were found between 10-week-old and 100-week-old diaphragms. Regarding the activity of SR Ca 2+ -ATPase, the pattern of age-related change was similar to that in the 1/2 relaxation time and there was a significant difference between 10-week-old and 100-week-old diaphragms. There was a significant increase in the relative composition of the MHC I isoform in 100-week-diaphragms compared to that in 10-week-old diaphragms and a concomitant decrease in the relative composition of fast myosin was noted. These findings demonstrated that older diaphragms have slower contraction and relaxation speeds, and these alterations were attributed to changes in SR Ca 2+ -ATPase activity and MHC isoform composition.Common age-related changes in physical functions include decreases in balance, visual acuity and hearing. With regard to skeletal muscles, changes such as muscle mass loss (18), lower muscle tension (9, 15), selective atrophy of fast-twitch fibers (16), and reduced mitochondrial enzyme and glycolytic enzyme activities (6) have been reported. These agerelated changes may cause falls, fractures and bed confinement, which are important social problems. Age-related changes in skeletal muscles have also been reported to affect not only the muscle fibers themselves, but also the oxygen supply to the cardiovascular system (22) and a decline in the number of spinal cord axons and nerve conduction velocity involved in contraction. Suppressing such age-related changes is considered important for successful aging. In rehabilitation, the diaphragm plays a wide variety of roles, including respiratory rehabilitation before and after surgery, home oxygen therapy for chronic obstructive pulmonary disease and cardiorespiratory responses in sports. Many rehabilitation therapists select abdominal breathing (diaphragmatic respiration) as the first-choice respiratory muscle exercise in acute and chronic patients. The diaphragm is the main action muscle of diaphragmatic respiration, and is always active in life maintenance; thus, when compared with other skeletal muscles, the diaphragm is more active. Hence, investigating chrono-