MSK-18 · Sports Medicine

Sports Medicine. Topics: Exercise Physiology, Cardiac Equations, and Muscle Physiology. Part of the Musculoskeletal series of the Reflex PM&R Board Review podcast. Audio corrections: (1) In the audio: climbing a single flight of stairs or performing light occupational work around an office or a house requires four to five mets. — Correct: One flight of stairs (about twelve steps) costs about 3 to 4 METs; two flights come to about 5. Light occupational work is what sits at 4 to 5 METs, which is separately the clearance threshold for most activities of daily living. (2) In the audio: Intensity mandates 40 to 85% of the heart rate reserve utilizing the Karvonen formula. — Correct: 40 to 89 percent of heart rate reserve: moderate intensity is 40 to 59 percent and vigorous is 60 to 89 percent. The 85 percent ceiling understates the vigorous band. (3) In the audio: An eccentric contraction naturally produces 20 to 50% more absolute force than a maximal isometric or concentric contraction executed at the exact same speed. — Correct: About 40 percent more force than a maximal concentric contraction at matched velocity (ratio near 1.4). Eccentric force also exceeds isometric force, but by a smaller and less precisely established margin. (4) In the audio: patients prescribe beta blockers must exclusively use perceived exertion instead of heart rate to monitor intensity. — Correct: A beta-blocker invalidates the age-predicted 220 minus age estimate, not heart-rate-reserve prescription. When a graded exercise test measured the peak on the current dose, a Karvonen target from that peak is an acceptable primary prescription; perceived exertion leads when no such test exists. (5) In the audio: Skeletal muscle extraction of oxygen only improves by about 10 to 20% with years of rigorous endurance training. — Correct: The direction is right but the 10 to 20 percent figure is unsourced. In short training programs, maximal cardiac output rises significantly while the maximal arteriovenous oxygen difference shows no significant average change; in heart failure the gain leans on peripheral adaptation instead. The written chapter is correct. Full correction register: https://www.reflexpmr.com/errata. The full companion chapter and a linked board-style Q-bank set for this topic are at https://www.reflexpmr.com/read/MSK-18.