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.

Atrial fibrillation is associated with significant symptoms, comorbidities, and shared pathophysiological features with heart failure with preserved ejection fraction. We propose that exercise testing, including cardiopulmonary exercise testing and exercise cardiac imaging, can unmask subclinical cardiac dysfunction, guide diagnosis and inform intervention. Exercise training has a key role in atrial fibrillation management, improving arrhythmia burden, atrial remodeling and quality of life.

Research is needed to understand how to motivate people to be active. There are wide individual differences in the reinforcing value of exercise, which predicts physical activity, and can be increased in sedentary adults. We include a computational model of how exercise reinforcement is related to physical activity and ideas on the choice between active versus sedentary alternatives.

Exercise is emerging as a powerful adjuvant therapy during cancer treatment, partly due to its immunomodulatory effects. However, the moderate- to vigorous-intensity exercise required for optimal immune-boosting effects is a barrier for many patients. β1 -selective blockade may bias β2 -adrenergic signaling to amplify immune responses at lower exercise intensities, offering a clinically feasible strategy for all cancer patients.

Limb disuse models, such as immobilization and limb suspension, have been implemented for 30+ yr to understand the mechanistic and clinical implications of neuromuscular impairments and muscle atrophy. Drawing on decades of experience, we outline key considerations for research design, ethics, and implementation. Serving as a roadmap for investigators, this review promotes broader use of disuse models in clinical trials.

Seasonal phase variation, characterized as a sinusoidal waveform anchored at the annual solstices, can be positively associated with both between- and within-person differences in physical activity in observational, longitudinal, and experimental studies. A continuous measure for adjusting seasonal phase variation will reduce seasonal confounding in physical activity research, increase the precision of effect sizes, and improve the reproducibility of findings.

Downregulation of microRNA-1 (miR-1), the most abundant muscle-enriched microRNA, represents a conserved hallmark of skeletal muscle hypertrophy across species. We propose that mechanical overload-induced reduction in miR-1 expression drives metabolic reprogramming critical for hypertrophic adaptation. This review explores emerging evidence establishing miR-1 as a master regulator of metabolism that governs skeletal muscle growth.

Acute physical exercise improves cognitive performance; however, the underlying physiological mechanisms are not yet fully understood. Here, we propose that enhanced neuromodulation is a crucial factor in the exercise-cognition interaction and present a future integrative framework to comprehensively understand these improvements.

Exercise in a hot environment can impair performance due to not only impaired coordination of major physiological systems but also reduced cognitive processing related to the exercise strategy. In this review, we discuss potential factors contributing to reduced exercise performance during excessive brain temperature elevation, with a focus on the functional localization of brain activity.

Current exercise guidelines for cancer survivors continue to rely on a binary separation of resistance and aerobic training. This review proposes a stimulus-based continuum in which mechanical load, cardiorespiratory strain, metabolic stress, recovery density, and contraction velocity collectively determine physiological adaptations. This framework provides a conceptual basis for designing time-efficient, individualized exercise strategies beyond traditional modality labels in cancer care.