Counterpoint: the interpolated twitch does not provide a valid measure of the voluntary activation of muscle

Muscle torque in total knee arthroplasty: comparison of subvastus and midvastus approaches

The subvastus and midvastus approaches are two of the most commonly performed quadriceps preserving approaches for total knee arthroplasty (TKA), which can hasten functional recovery and rehabilitation. However, there has not been sufficient investigation with respect to a quantitative comparison between the two approaches in terms of muscle strength. To compare outcomes with respect to muscle strength between these two approaches, quadriceps and hamstring muscle torques of 20 patients who underwent primary TKA with the subvastus (SV) approach and 10 patients who received the midvastus (MV) approach were measured after surgery. The median age of patients in the SV group (68 years, range 53-77 years) was significantly different that the median age of patients in the MV group (61 years, range 50-73 years) (P = 0.0141). There was no significant difference in patient weight, height, or postoperative duration before muscle testing between the SV and MV groups. There were no significant differences in peak muscle torque or hamstring/quadriceps (H/Q) ratio between the groups. We thus conclude peak muscle torque and H/Q ratios were not statistically different with the SV or MV approach, therefore functional outcome is comparable.

Functional consequences of sarcopenia and dynapenia in the elderly

PURPOSE OF REVIEW

The economic burden due to the sequela of sarcopenia (muscle wasting in the elderly) are staggering and rank similarly to the costs associated with osteoporotic fractures. In this article, we discuss the societal burden and determinants of the loss of physical function with advancing age, the physiologic mechanisms underlying dynapenia (muscle weakness in the elderly), and provide perspectives on related critical issues to be addressed.

RECENT FINDINGS

Recent epidemiological findings from longitudinal aging studies suggest that dynapenia is highly associated with both mortality and physical disability even when adjusting for sarcopenia indicating that sarcopenia may be secondary to the effects of dynapenia. These findings are consistent with the physiologic underpinnings of muscle strength, as recent evidence demonstrates that alterations in muscle quantity, contractile quality and neural activation all collectively contribute to dynapenia.

SUMMARY

Although muscle mass is essential for regulation of whole body metabolic balance, overall neuromuscular function seems to be a critical factor for maintaining muscle strength and physical independence in the elderly. The relative contribution of physiologic factors contributing to muscle weakness are not fully understood and further research is needed to better elucidate these mechanisms between muscle groups and across populations.

Running versus strength-based warm-up: acute effects on isometric knee extension function

This study investigated the influence of two warm-up protocols on neural and contractile parameters of knee extensors. A series of neuromuscular tests including voluntary and electrically evoked contractions were performed before and after running- (R(WU); slow running, athletic drills, and sprints) and strength-based (S(WU); bilateral 90 degrees back squats, Olympic lifting movements and reactivity exercises) warm ups (duration approximately 40 min) in ten-trained subjects. The estimated overall mechanical work was comparable between protocols. Maximal voluntary contraction torque (+15.6%; P < 0.01 and +10.9%; P < 0.05) and muscle activation (+10.9 and +12.9%; P < 0.05) increased to the same extent after R(WU) and S(WU), respectively. Both protocols caused a significant shortening of time to contract (-12.8 and -11.8% after R(WU) and S(WU); P < 0.05), while the other twitch parameters did not change significantly. Running- and strength-based warm ups induce similar increase in knee extensors force-generating capacity by improving the muscle activation. Both protocols have similar effects on M-wave and isometric twitch characteristics.