Maximum Voluntary Activation in Nonfatigued and Fatigued Muscle of Young and Elderly Individuals

Abstract

Background and Purpose. Researchers studying central activation of muscles in elderly subjects (≥65 years of age) have investigated activation in only the nonfatigued state. This study examined the ability of young and elderly people to activate their quadriceps femoris muscles voluntarily under both fatigued and nonfatigued conditions to determine the effect of central activation failure on age-related loss of force. Subjects and Methods. Twenty young subjects (11 men, 9 women; mean age=22.67 years, SD=4.14, range=18–32 years) and 17 elderly subjects (8 men, 9 women; mean age=71.5 years, SD=5.85, range=65–84 years) participated in this study. Subjects were seated on a dynamometer and stabilized. Central activation was quantified, based on the change in force produced by a 100-Hz, 12-pulse electrical train that was delivered during a 3- to 5-second isometric maximum voluntary contraction (MVC) of the quadriceps femoris muscle. Next, subjects performed 25 MVCs (a 5-second contraction with 2 seconds of rest) to fatigue the muscle. During the last MVC, central activation was measured again. Results. In the nonfatigued state, elderly subjects had lower central activation than younger subjects. In the fatigued state, this difference became larger. Discussion and Conclusion. Central activation of the quadriceps femoris muscle in elderly subjects was reduced in both the fatigued and nonfatigued states when compared with young subjects. Some part of age-related weakness, therefore, may be attributed to failure of central activation in both the fatigued and nonfatigued states.

Using submaximal contractions to predict the maximum force‐generating ability of muscles

“…A cubic equation more closely fit the data from the present study. Stackhouse and colleagues [5][6][7]9 plotted CAR against percent maximal volitional effort (%MVE). However, in this study, we wanted to adjust MFGA predictions for individuals with an unknown true MFGA, which is similar to how this technique will be used in clinical situations.…”

“…[1][2][3][4][5][6][7][8] Determining specific causes of the muscle weakness in neurologically impaired populations may be important for choosing appropriate rehabilitation programs for each patient. [5][6][7]9 For example, strength training may be sufficient to increase strength in individuals who have considerable muscle atrophy and minimal neurological impairment. In contrast, individuals with high degrees of neurological impairment due to decreased central activation may require rehabilitation programs that involve electrical stimulation or biofeedback to better activate their muscles and therefore achieve greater strength gains.…”

“…2,[5][6][7]9,10 VAR ¼ 1 means the muscle is fully activated by the volitional effort. 2,[5][6][7] VAR <1 means the individual is not fully activating the muscle. [5][6][7] F vol is typically measured isometrically and can be directly measured using a force dynamometer.…”

“…1 Previous studies have used the burst superimposition technique to estimate the MFGA in individuals with no neurological impairment. 2,5,7,9,11 During the burst superimposition technique, a train of maximal electric pulses is delivered to the subject during a maximal voluntary isometric contraction. The MFGA of the muscle is the total force produced by the volitional contraction and the stimulation.…”

“…It tends to overestimate the activation of a muscle at submaximal volitional levels 5,6 and may be an insensitive estimate of activation at high volitional effort. 7,9 An equation that corrects the predicted VAR has been tested for evaluating the quadriceps femoris muscles 5,6,9,11 of healthy adults, 5 those with anterior cruciate ligament (ACL) injury, 11 and older adults. 6,9 The accuracy of the predicted VAR has not been determined in individuals with nervous system pathologies, 15,17 and the equation used to correct the burst superimposition technique for the quadriceps femoris muscles has not been validated for use in any other muscle group.…”