Cardio: fat‑loss and endurance

A January 24, 2026 meta‑analysis of randomized trials concluded that HIIT produced equal or greater reductions in body fat and similar or larger VO2max gains than time‑matched moderate‑intensity continuous training (MICT). (link.springer.com)) Work:rest ratios matter — a 1:2 ratio (20s hard, 40s recovery) is a recognized HIIT scheme that trainers use to preserve power across rounds, with progressions commonly starting at 6 rounds and moving to 8–10 rounds as fitness improves. (5minutetimer.org)) Exercise scientists and programming guides that summarize the ACSM/WHO frameworks commonly place HIIT volume at roughly 2 sessions per week for recreational trainees, delivering about 8–10 minutes of high‑intensity work inside 15–25 minute sessions to meet vigorous‑activity targets of 75–150 minutes per week. (hiitscience.com)) Long ultraendurance events repeatedly show measurable muscle stress and net tissue loss: systematic reviews of 24‑hour and multi‑day ultramarathons report decreases in body mass that can include skeletal muscle, and a 50 km field study documented acute changes in muscle thickness and strength after the race. (link.springer.com)) Randomized trials and meta‑analyses show lean‑mass preservation when resistance training is included during dieting, and many clinical trials testing preservation strategies use protein intakes around 1.6 g/kg/day (some trials testing up to 3.2 g/kg) alongside resistance work. (bmjopensem.bmj.com)) Practical takeaway from protocols and reviews: aim for short, repeatable HIIT blocks (20s/40s or similar) inside twice‑weekly sessions, keep total weekly vigorous minutes within WHO/ACSM ranges, and combine with twice‑weekly resistance training plus ~1.6 g/kg/day protein to blunt muscle loss during fat loss phases. (trainingpeaks.com))