Advances in Physiology of Training—3rd Edition

Objectives: Circadian rhythms regulate key physiological processes, including metabolism and energy balance. Emerging evidence suggests that the timing of physical activity may influence metabolic outcomes. However, how the timing of endurance exercise impacts long-term metabolic health and the role of the circadian clock in this process remain unclear. This study aimed to investigate whether time-dependent endurance exercise improves metabolic health via circadian rhythm regulation. Methods: A 12-week endurance exercise protocol was established using wild-type (WT) and circadian-disrupted Clock^Δ19 mice. Mice were assigned to exercise at Zeitgeber time 0 (ZT0) or Zeitgeber time 0 (ZT12), or to sedentary controls. Assessments included rotarod fatigue test, body weight, epididymal fat ratio, fasting blood glucose, serum triglycerides, high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), non-esterified fatty acids (NEFA), intraperitoneal glucose tolerance test (IPGTT), and insulin tolerance test (ITT). Results: Clock^Δ19 mice exhibited circadian phase-dependent fatigue susceptibility on the rotarod, particularly at ZT0. Both exercised Clock^Δ19 groups (ZT0 and ZT12) showed significant weight reduction compared to sedentary controls, indicating that endurance exercise may counteracts circadian disruption-induced weight gain independent of timing. In WT mice, evening exercise (ZT12) led to enhanced lipid regulation and better glucose tolerance. These time-dependent benefits were absent in Clock^Δ19 mutants, demonstrating that the full metabolic advantages of exercise require a functional circadian clock. Notably, endurance training also partially restored serum HDL-C levels in Clock^Δ19 mice, suggesting compensatory metabolic responses. Conclusions: Aligning endurance exercise with the body’s internal clock provides greater metabolic benefits than untimed exercise. The circadian clock is essential for time-dependent improvements in glucose and lipid metabolism, although some beneficial effects occur independently of a functional clock. Full article

Background: COVID-19 has been associated with persistent impairments in autonomic modulation of heart rate variability (HRV). However, whether disease severity during the acute phase influences the magnitude of these impairments remains insufficiently explored. In turn, aerobic physical training (APT) has been proposed as a countermeasure to autonomic dysfunction of HRV in different conditions, although its effects in individuals with COVID-19 are not yet well established. To address these gaps, this study investigated the consequences of COVID-19 on autonomic modulation of HRV according to disease severity and evaluated the effects of APT on this parameter. Methods: One hundred and sixteen individuals (58 men and 58 women) aged between 30 and 55 years were included, allocated into three groups according to the severity of the disease in the acute phase: Mild group (n = 38, mean age: 48 ± 7 years); Moderate group (n = 52, mean age: 43 ± 5 years); and Severe group (n = 26, mean age: 45 ± 6 years). All groups had anthropometric and hemodynamic parameters evaluated before and after the 16-week APT period, as well as parameters of autonomic modulation of HRV analyzed using linear (time and frequency domain) and non-linear (symbolic analysis) methods obtained from R–R interval (RRi) recordings in the supine position for 30 min. Results: Initially, all groups presented similar anthropometric and hemodynamic values. In contrast, the Moderate and Severe groups presented lower values for standard deviation of normal RRi (SDNN; Moderate: 38 ± 14 ms; Severe: 33 ± 12 ms vs. Mild: 55 ± 28 ms; p < 0.001), root mean square difference between adjacent normal RRi (RMSSD; Moderate: 28 ± 13 ms; Severe: 22 ± 7 ms vs. Mild: 47 ± 38 ms; p < 0.001), total variance (Moderate: 203 ± 127 ms²; Severe: 303 ± 157 ms² vs. Mild: 526 ± 347 ms²; p < 0.001), and high-frequency (HF) oscillations in absolute units (Moderate: 259 ± 270 ms²; Severe: 153 ± 74 ms² vs. Mild: 438 ± 421 ms²; p < 0.001), both compared to the Mild group. In turn, the Severe group, when compared to the other groups, also presented lower HF oscillations (Severe: 29 ± 12 nu vs. Mild: 44 ± 17 nu and Moderate: 42 ± 17 nu; p < 0.001) and higher low-frequency (LF) oscillations (Severe: 71 ± 12 nu vs. Mild: 60 ± 17 nu and Moderate: 58 ± 17 nu; p < 0.001), but in normalized units. After the 16-week APT, all groups showed increases in HF oscillations (Mild: −206 ms² and −19.12 nu; Moderate: −236 ms² and −26.7 nu; Severe: −211 ms² and −31.0 nu; p < 0.001) and reductions in LF oscillations (Mild: 198 ms² and 19.01 nu; Moderate: 98 ms² and 26.7 nu; Severe: 218 ms² and 31.1 nu; p < 0.001), both in absolute and normalized units. In this case, there were no further differences in LF and HF oscillations between the groups. Conclusions: Individuals who had COVID-19 and developed moderate to severe cases showed greater impairments in the autonomic modulation of HRV, characterized by increased sympathetic autonomic modulation and reduced vagal modulation. In turn, APT as a countermeasure appears to increase vagal autonomic modulation and reduce sympathetic autonomic modulation of HRV, regardless of the previous severity of COVID-19. Full article

Listening to music is a well-established strategy to enhance exercise capacity, yet the specific mechanisms linking music choice to performance enhancement remain fragmented. This scoping review systematically summarizes the existing literature on the effects of music choice (i.e., self-selected, preferred music) on performance and psychophysiological determinants of exercise capacity to establish an updated rationale for the use of personalized music interventions in training. Following PRISMA-ScR guidelines, a systematic search of five databases (PubMed, Web of Science, Embase, Scopus, CINAHL) was performed for studies published between January 2000 and April 2025. Peer-reviewed articles investigating the ergogenic effects of self-selected or preferred music with psychophysiological outcomes were included. Thirty-two studies met inclusion criteria. Overall, evidence supports consistent performance enhancement from choice music (CM) across modes of exercise including aerobic endurance, anaerobic power, and muscular endurance activities while maximal strength was largely unaffected. The most robust and consistent mechanisms underpinning the benefits of CM during exercise were psychological in nature, including improvements in affect, arousal, motivation, and perception of exertion. Notable physiologic benefits were also identified, including altered cortical excitability, autonomic modulation, and improvements in neuromuscular efficiency. Herein, this review provides a psychophysiological framework whereby CM acts as a primary mediator to induce psychological and physiological cascades which synergistically contribute to ergogenic benefits. Evidence heavily supports the superiority of CM to improve exercise performance across various modalities. Full article