Neuromuscular electrical stimulation after total joint arthroplasty: a critical review of recent controlled studies.

Since 2009, four randomized controlled trials have investigated the use of Neuromuscular Electrical Stimulation (NMES) as a treatment modality following total knee arthroplasty (TKA). Two of these studies demonstrated a treatment effect of NMES for improving physical function, while another study failed to find additional benefit of NMES relative to a progressive exercise intervention. The fourth study demonstrated non-inferiority of NMES compared supervised physical therapy. These studies differed substantially in their methodology, including the timing, duration, treatment volume and intensity of NMES interventions. The purpose of this review is to examine and discuss variations between these recent trials to synthesize the current state of evidence for NMES in post-TKA rehabilitation. When comparing intervention parameters across recent studies, it appears that high intensity NMES performed regularly during the immediate postoperative phase helped to attenuate dramatic losses in quadriceps strength following TKA, thereby resulting in overall improvements in strength and function.

Challenging the role of pH in skeletal muscle fatigue.

Muscle fatigue is frequently defined as a temporary loss in force- or torque-generating ability because of recent, repetitive muscle contraction (1). The development of this temporary loss of force is a complex process and results from the failure of a number of processes, including motor unit recruitment and firing rate, chemical transmission across the neuromuscular junction, propagation of the action potential along the muscle membrane and T tubules, Ca2+ release from the sarcoplasmic reticulum (SR), Ca2+ binding to troponin C, and cross-bridge cycling (for detailed reviews, see Bigland-Ritchie and Woods(1), McLester(2), and Favero(3)). Muscle fatigue may limit the time a person can stand, the distance a person can ambulate, or the number of stairs a person can ascend or descend. In practical terms, however, we cannot know what actually leads to a decline in function for a given patient. For a phenomenon that may have profound clinical implications, muscle fatigue often receives inadequate attention in physiology textbooks, many of which contain a page or less of information on the entire topic (4-8). In addition, many textbooks report that muscle fatigue is mainly the result of a decrease in pH within the muscle cell due to a rise in hydrogen ion concentration ([H+]) resulting from anaerobic metabolism and the accumulation of lactic acid (6-8). Recent literature, however, contradicts this assertion (9-10). The purpose of this update, therefore, is to provide a brief review of the role of pH in the development of muscle fatigue.

Maximum voluntary activation in nonfatigued and fatigued muscle of young and elderly individuals.

BACKGROUND AND PURPOSE: Researchers studying central activation of muscles in elderly subjects (> or = 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.

Measurement of central activation failure of the quadriceps femoris in healthy adults.

The purpose of this investigation was to describe the relationship between the central activation ratio (CAR) and the percent maximum voluntary effort (% MVE) during isometric quadriceps femoris contractions. Twenty-one healthy, young adults participated in three test sessions. During each session, one of three train types was tested: a 100-HZ 120-ms train, a 100-HZ 250-ms train, or a 50-HZ 500-ms train. Subjects were seated on a force dynamometer and stabilized to perform a 3-5-s isometric knee extension at MVE. Force targets were set at 25, 50, 75, and 100% of the MVE. With 5 min rest between efforts, subjects produced forces at the specified target levels. When each target was reached, the test train was delivered to quantify the amount of central activation. There were no significant differences in CARs across train types during maximal efforts, but during submaximal efforts at 25 and 50%, the 100-HZ 250-ms and 50-HZ 500-ms trains produced significantly lower CARs than the 100-HZ 120-ms train. The relationship between the CAR and the %MVE was curvilinear and best described by a second-order polynomial for all three train types. If tests of central activation are going to be used clinically, it is important to know the relationship between the CAR and voluntary effort; however, further study will be required to extend these results to specific patient populations.