Swimming Physiology
Authors: Ingvar Holmér
DOI / Source: Annals of Physiological Anthropology 11(3):269–276 (1992)
Date: 05 March 1992
Reading level: Beginner
Why This Matters for Freedivers
Freediving (especially dynamic and finning) rewards the same thing swimming does: moving through water with the lowest possible energy cost. This paper gives a simple “physics + body” explanation for why technique improvements often beat just trying harder: drag rises fast with speed, and cleaner movement saves oxygen and delays CO₂ build-up.
Synopsis
This is a short, classic overview of what makes swimming physiologically “different” from land exercise, and why technique matters so much. Holmér starts with a simple point: water is a totally different environment—higher resistance, different breathing constraints, and different circulation and heat-loss conditions than running or cycling.
A big theme is drag and efficiency. As swimming speed increases, the energy cost rises steeply, mainly because resistance increases. That means small technique gains (streamlining, better body position, smoother propulsion) can have a surprisingly large effect on how hard a given pace feels. The paper also points out that some strokes cost more energy at the same speed than others—front crawl is generally the cheapest, with butterfly and breaststroke being more expensive.
Another useful concept is the “performance equation” style idea: your top speed isn’t just about how much energy your body can produce—it’s also about how much resistance you’re fighting and how efficiently you turn effort into forward motion (page 3). The takeaway is very coach-friendly: you can improve performance by improving aerobic/anaerobic capacity, or by reducing drag and improving technique—and the technique side is often undertrained because it’s harder to measure.
The paper then compares key physiological responses in swimming vs running. One consistent difference is that max heart rate is lower in swimming (around 10–15 beats/min lower at maximal effort is mentioned), even when oxygen uptake can be similar at a given submax workload (page 5). Breathing is also constrained by stroke rhythm and body position, which changes how ventilation behaves during hard efforts.
Finally, Holmér discusses training implications: performance comes from a mix of physical capacity and biomechanics, and swim training needs a balance of aerobic conditioning, anaerobic work, strength/power, and skill/technique practice (page 6). The overall message is practical: for water sports, “getting fitter” matters, but getting more efficient can matter just as much—or more.
Abstract
Swimming takes place in water, which presents different gravitational and resistive forces and different respiratory and thermal stress compared to air. The energy cost of propulsion is high, but can be reduced at a given speed through regular training and improved technique. Swimming performance depends on both physiological capacity (aerobic and anaerobic power, cardiovascular and respiratory function) and technical factors that influence efficiency and resistance. Maximal heart rate tends to be lower in swimming than in running, and breathing constraints imposed by stroke mechanics influence ventilation. Rational principles based on biomechanics and physiology should guide training and coaching.