The Affects Of Aging On Skeletal Muscle — страница 3

dynamic contractions, and is in agreement with previous studies. (Lindstrom et al.1997) Slowed Muscle Contractile Properties are not Associated with a Decreased EMG/Force Relationship in Older Humans Alexander V. Ng and Jane A. Kent-Braun Ng and Kent-Braun (1999) tested the hypothesis that as a result of slower muscle contractile properties, the EMG force relationship decreased during voluntary contractions in older compared to young humans. The group consisted of 12 men and 10 women aged 25 ? 44 and 9 men and 11 women aged 65 ? 82. The volunteers were healthy nonsmoking individuals that had no more than two regular exercise sessions per week for the previous three months. (Ng & Kent-Braun, 1999) To measure force/frequency relationship the peak muscle force during

supramaximal, electrically stimulated contractions of 1 s duration at 1, 5, 10, 20, and 50 Hz. The measurements were obtained after the twitch and CMAP (compound muscle action potential) measurements were taken. (Ng & Kent-Braun, 1999) The maximal voluntary isometric contraction (MVC) force was obtained after the data for the stimulated force-frequency relationship. Three MVC?s were obtained, each during a voluntary 3-5 s maximal dorsi flexion. One minute of rest separated each MVC measurement. (Ng & Kent-Braun, 1999) To study possible changes in the EMG force relationship with age, the subjects performed graded, non-fatiguing isometric contractions from 10% to 100% MCV in 10% increments. Contractions were 10 s in duration and separated by one minutes rest. (Ng &

Kent-Braun, 1999) The results of this study showed that in addition to slower dorsi flexion contraction properties, the older compared to the young subjects had an increase in relative force production during low frequency stimuli. Despite this relative increase in force production, the surface EMG at low voluntary force levels was increased, not decreased, compared to younger adults. Thus, slowed muscle contractile properties in older compared to younger adults did not lead to a decreased EMG force relationship. Therefore, slower muscle contractile properties in older adults do not result in increased neural efficiency during voluntary contraction. (Ng & Kent-Braun, 1999) Gender Differences in Isometric Contractile Properties and Fatigability in Elderly Human Muscle Audrey

L. Hicks and Neil McCartney This paper compares the isometric contractile characteristics and fatigability of the elbow flexors and ankle dorsi flexors in healthy males and females between 60 and 80 years, and examines the effects of 22 months of resistance training on these variables. (Hicks, A. L. & McCartney, N. 1996) Resistance training took place twice a week, on alternate days. The training program was designed to involve several muscle groups, including the elbow flexors and ankle dorsi flexors. The exercises were completed using a circuit set system, with 2-minute rests between sets; each set consisted of either 10 (arms) or 12 (legs) repetitions. The training progressed from 2 sets of each exercise at 50% 1RM (one rep maximum) over the course of the study. The 1RM

was measured every 6 weeks, and the training loads were adjusted accordingly. The muscle contractile properties were measured at three time points– baseline, 10 months, and 22 months. (Hicks, A. L. & McCartney, N. 1996) When compared to younger adults, the muscles of older individuals are smaller, weaker, and slower to contract. In this study the isometric and contractile speed of both the elbow flexors and ankle dorsi flexors were weaker and slower in older adults than in younger adults. Although the older subjects had smaller evoked Pts for the elbow flexors compared to that in younger adult, the Pts for the ankle dorsi flexors were not unlike those reported in the younger subjects. (Hicks, A. L. & McCartney, N. 1996) The measurement of muscle fatigue during voluntary

isometric effort revealed a notable gender difference in fatigue resistance in the population, with female possessing a significantly greater endurance than males. Two years of twice weekly dynamic resistance training resulted in virtually no changes in the isometric contractile properties or fatigability, despite very significant gains in dynamic strength. (Hicks, A. L. & McCartney, N. 1996) Summary The studies reviewed did not find definite results that aging affects specific strength, contractile properties, decreased EMG/force relationship, or endurance in older human muscle. Ng and Kent-Braun did however suggest during the study that testosterone might play a role in differentiating the strength of young men from older men. They also suggested that relative