Muscle models underpin how exercise, rehabilitation, and human-movement sciences infer muscle force during activity, yet profound gaps remain between traditional measures and models of muscle function and the dynamic features of muscle in natural movement. We review evidence for these gaps, highlight new experiments to bridge them, and suggest directions to improve models of dynamic muscle function. Summary : We propose reframing muscle as a dynamic mechanical system, integrating new experiments and models to predict function during natural movement.
Detecting exercise intensity thresholds is key for optimizing endurance training prescriptions for performance and recovery. Over the past several years an index of heart rate variability representing fractal correlation properties (DFA a1) has been investigated with respect to exercise intensity threshold demarcation and durability. We intend to show that sufficient data has accumulated to recommend it for widespread consumer use in tested populations. Summary: Validated consumer hardware, software, along with strong study results, support using DFA a1 monitoring to evaluate training zones and durability.
Physiological stress of environmental exposure and energy deficit impairs the absorption, transport, and utilization of exogenous carbohydrate for fuel during exercise. Blunted exogenous carbohydrate oxidation may require alternative fueling strategies to optimize carbohydrate metabolism to support physical performance. This review will overview the impact of physiological stress on exogenous carbohydrate oxidation and potential interventions to support physical performance. Summary: Physiological stress exposure limits the effectiveness of carbohydrate supplementation to spare endogenous substrate oxidation by impeding exogenous carbohydrate oxidation.
The SSC effect – increased force, work, and power during shortening of stretch-shortening cycles compared with shortening alone – has long been attributed to stretch reflexes, preactivation, elastic recoil, and muscle-tendon unit decoupling. However, we hypothesize that contractile component mechanisms related to residual force enhancement can contribute substantially to the SSC effect. This article reviews current evidence for this history-dependent SSC-effect hypothesis. Summary: The contractile mechanism underlying residual force enhancement, especially titin, can substantially contribute to the stretch-shortening cycle effect.
