Simple equations to predict concentric lower-body muscle power in older adults using the 30-second chair-rise test: a pilot study.

Although muscle power is an important factor affecting independence in older adults, there is no inexpensive or convenient test to quantify power in this population. Therefore, this pilot study examined whether regression equations for evaluating muscle power in older adults could be derived from a simple chair-rise test. We collected data from a 30-second chair-rise test performed by fourteen older adults (76 +/- 7.19 years). Average (AP) and peak (PP) power values were computed using data from force-platform and high-speed motion analyses. Using each participant's body mass and the number of chair rises performed during the first 20 seconds of the 30-second trial, we developed multivariate linear regression equations to predict AP and PP. The values computed using these equations showed a significant linear correlation with the values derived from our force-platform and high-speed motion analyses (AP: R = 0.89; PP: R = 0.90; P < 0.01). Our results indicate that lower-body muscle power in fit older adults can be accurately evaluated using the data from the initial 20 seconds of a simple 30-second chair-rise test, which requires no special equipment, preparation, or setting.

Correlation analyses and regression modeling between isokinetic testing and on-court performance in competitive adolescent tennis players.

Tennis requires skill, physical attributes, and strategy. Ball velocity and placement are two of the most important components in winning the faster-paced modern game. Although isokinetic testing has been used to evaluate physical characteristics and injury potential in tennis players, few studies have compared isokinetics and on-court performance. Such a comparison would help establish links between speed-specific properties of functioning muscles and stroke production and could affect overall training strategy. This study compared isokinetic peak torque (PT), average power (AP), and total work (TW) during specific testing patterns correlated with ball velocity or stroke accuracy during the service, forehand, and backhand and developed predictive equations for each stroke using these variables. Thirty-five players, aged 13-18 years with at least 4 years playing experience, were evaluated using internal and external shoulder rotation, leg extension, and diagonal throwing motions. Ball velocity was measured using a radar gun. Accuracy was evaluated on the basis of shot position and depth. Significant correlations were found between ball velocity and a number of isokinetic variables, while no significant correlations were observed with shot accuracy. Significant isokinetic variables for each stroke were entered into regression models. One isokinetic speed sufficiently predicted ball velocity for each stroke, since no increase in predictive capacity was observed with the addition of other isokinetic parameters. We conclude that isokinetics at testing speeds between 1.57 and 4.71 rad.s(-1) can effectively predict ball velocity, but not accuracy, and that our results may be helpful in planning strategies for training and rehabilitation.

Alteration of contractile force and mass in the senescent diaphragm with beta(2)-agonist treatment.

Aging is associated with a decrease in diaphragmatic maximal tetanic force production (P(o)) in senescent rats. Treatment with the beta(2)-agonist clenbuterol (CB) has been shown to increase skeletal muscle mass and P(o) in weak locomotor skeletal muscles from dystrophic rodents. It is unknown whether CB can increase diaphragmatic mass and P(o) in senescent rats. Therefore, we tested the hypothesis that CB treatment will increase specific P(o) (i.e., force per cross-sectional area) and mass in the diaphragm of old rats. Young (5 mo) and old (23 mo) male Fischer 344 rats were randomly assigned to one of the following groups (n = 10/group): 1) young CB treated; 2) young control; 3) old CB treated; and 4) old control. Animals were injected daily with either CB (2 mg/kg) or saline for 28 days. CB increased (P < 0.05) the mass of the costal diaphragm in both young and old animals. CB treatment increased diaphragmatic-specific P(o) in old animals (approximately 15%; P < 0.05) but did not alter (P > 0.05) diaphragmatic-specific P(o) in young animals. Biochemical analysis indicated that the improved maximal specific P(o) in the diaphragm of CB-treated old animals was not due to increased myofibrillar protein concentration. Analysis of the myosin heavy chain (MHC) content of the costal diaphragm revealed a CB-induced increase (P < 0.05) in type IIb MHC and a decrease in type I, IIa, and IIx MHC in both young and old animals. These data support the hypothesis that CB treatment can restore the age-associated decline in both diaphragmatic-specific P(o) and muscle mass.