High-intensity interval training (HIIT) is an exercise modality acknowledged to maintain physical fitness with more engagement in an active lifestyle compared with other traditional exercise models. Nevertheless, its effects on cardiac control and physical performance in an online-guided setting are not yet clarified. The present work assessed physical fitness and heart rate variability (HRV) before and after an online, home-based HIIT program in college-age students while pandemic lockdowns were in effect. Twenty university students (age: 21.9 ± 2.4 years.) that were solely enrolled in online classes were distributed into three groups: control—CON-(n = 6), 14 min of HIIT—HIIT-14-(n = 8), and 21 min of HIIT—HIIT-21-(n = 6). A maximal push-up test was employed to assess muscular endurance and performance, and resting HRV signals were collected with wireless heart rate monitors and were processed in Kubios HRV Std. (Kubios Oy, Finland). There was an increase in total push-up capacity compared to CON (p < 0.05 HIIT-21 vs. CON; p < 0.001 HIIT-14 vs. CON) after 8 weeks. A significant interaction was observed in high-frequency and low-frequency spectra ratios after the HIIT-21 intervention (p < 0.05). The current work demonstrated that either short- or mid-volume online, whole-body HIIT improves muscle strength, whereas mid-volume HIIT (HIIT-21) was the only intervention that developed a sympathovagal adaptation. This study showed promising results on muscular endurance and cardiac autonomic modulation through whole-body HIIT practice at home.

Combined functional training (FT), high-intensity interval training (HIIT) and aquatic exercise may improve health-related fitness in aging populations; however, the influence of baseline adiposity on training responses remains unclear. This study evaluated the effects of a 12-week multicomponent training program on aerobic capacity, body composition, metabolic health, and physical performance in middle-aged and older women and explored whether baseline body fat percentage modulated these responses. Thirty-four women (50–72 years) were assigned to a control group (Ctrl, n = 10) or an exercise group, stratified into normal fat (NF%, n = 10) and high fat (HF%, n = 14). The intervention included three weekly 60 min sessions consisting of HIIT, FT, and aquatic-based interval and resistance exercises, while controls maintained their habitual lifestyle without structured exercise. Significant improvements were observed in VO₂max, skeletal muscle mass, fasting insulin, triglycerides, total cholesterol, HDL cholesterol, and functional performance. Baseline adiposity influenced metabolic adaptations, with greater improvements in the HF% group. These findings suggest that multicomponent training may improve cardiometabolic health and physical performance; however, the results should be interpreted cautiously due to the quasi-experimental design and small sample size.