Strength training improves the steadiness of slow lengthening contractions performed by old adults

Abstract

When old adults participate in a strength-training program with heavy loads, they experience an increase in muscle strength and an improvement in the steadiness of submaximal isometric contractions. The purpose of this study was to determine the effect of light- and heavy-load strength training on the ability of old adults to perform steady submaximal isometric and anisometric contractions. Thirty-two old adults (60-91 yr) participated in a 4-wk training program of a hand muscle. Both the light- and heavy-load groups increased one-repetition maximum and maximal voluntary contraction (MVC) strength and experienced similar improvements in the steadiness of the isometric and shortening and lengthening contractions. The increase in MVC strength was greater for the heavy-load group and could not be explained by changes in muscle activation. Before training, the lengthening contractions were less steady than the shortening contractions with the lightest loads (10% MVC). After training, there was no difference in steadiness between the shortening and lengthening contractions, except with the lightest load. These improvements were associated with a reduced level of muscle activation, especially during the lengthening contractions.

Fluctuations in motor output of a hand muscle can be altered by the mechanical properties of the position sensor

“…In tasks requiring steady index-finger movement, the fluctuations in acceleration and power below ∼12 Hz are greater when the finger is not attached to the LVDT (Wessberg and Kakuda, 1999;Wessberg and Vallbo, 1996) compared with when it is connected to the LVDT (Laidlaw et al, 1999;Shinohara et al, 2005a). Although the LVDT comprises a low-friction mechanism, its attachment to the index finger may have attenuated the fluctuations in motor output in previous studies Kornatz et al, 2005;Laidlaw et al, 1999;Shinohara et al, 2005a) and changed the frequency content as observed previously (Wessberg and Kakuda, 1999;Wessberg and Vallbo, 1996).…”

“…Although the LVDT comprises a low-friction mechanism, its attachment to the index finger may have attenuated the fluctuations in motor output in previous studies Kornatz et al, 2005;Laidlaw et al, 1999;Shinohara et al, 2005a) and changed the frequency content as observed previously (Wessberg and Kakuda, 1999;Wessberg and Vallbo, 1996). The absence of a correlation between measures of fluctuations, therefore, may be due to the potential distortion of the signals by the LVDT.…”

“…In addition, the absence of an interaction between condition (LVDT and no LVDT) and contraction type for both SDs indicates that the influence of the LVDT was similar across contraction types. Therefore, findings from previous studies that used the LVDT during contractions with the first dorsal interosseus muscle Kornatz et al, 2005;Laidlaw et al, 2002;Laidlaw et al, 1999;Shinohara et al, 2005a) provide valid measures of the magnitude of the fluctuations despite the friction of the LVDT.…”

“…A number of studies have previously measured finger displacement with the LVDT Kornatz et al, 2005;Laidlaw et al, 1999;Shinohara et al, 2005a). The linear relation between the displacement SD measured by the LVDT and the laser displacement sensor (Fig.…”

“…In experimental studies, the amount of fluctuations in movement during steady contractions has been typically quantified as the standard deviation (SD) of displacement (Laidlaw et al, 1999;Manini et al, 2005;Tracy and Enoka, 2002) or as the SD of acceleration Graves et al, 2000;Kornatz et al, 2005). However, Shinohara et al (2005a) found only minor correlations between these two measures of fluctuations during steady contractions with the first dorsal interosseus muscle when displacement of the index finger was measured with a linear variable-displacement transducer (LVDT; Novotechnik, Stuttgart, Germany) and acceleration was determined with a miniature piezoresistive accelerometer as young and old subjects slowly lifted and lowered a weight that ranged between 2.5% and 40% of the subject's maximal force.…”