By Daniel G. Graetzer, Ph.D.
Faculty Member, School of Health Sciences
Exercise in the water has a vastly different impact on the body as compared to running or cycling on land. One obvious difference in swimming is that more energy must be exerted to maintain buoyancy and power the body forward in the water.
Split Times for Triathlon Swimming Are Better in Salt Water
An interesting comparison of triathlon times has shown that split times (the time it takes to move a specific distance) for swimming are better in salt water than fresh water. Remember your high school physics: the higher the density of a solution (the more salt in water, for instance), the better you will float.
This increased buoyancy in salt water is likely one reason why very few drownings occur in Utah’s Great Salt Lake. It could also be a reason why faster swimming splits are seen in Hawaii’s Iron Man triathlon as compared to freshwater swimming competitions of equal distance (assuming an equal current flow in the water).
The Growth of Triathlons and Other Competitions
If you have aspirations of becoming a triathlete, the Iron Man Triathlon begins with a 2.4-mile swim in the Pacific Ocean. It is then followed by a 112-mile bike over hilly terrain and finishes with a 26.22-mile bike marathon in the sweltering heat. Hawaii’s first Iron Man was held in 1978 with 15 starters and 12 finishers.
Since this humble beginning, triathlons have experienced tremendous growth. There are tens of thousands of competitions nationwide and events range from the “paper man” level (often a 100-meter swim, 3-mile bike, 0.5-mile run) to the ultra-triathlon level. If you’re not challenged enough by these competitions, the International Ultra-Triathlon Association (IUTA) now sponsors events that include continuous and one-a-day options for double, triple, quintuple, and even deca-triathlons.
Swimming Requires More Energy to Move the Body Forward
Metabolic comparisons have shown that the energy cost of swimming a given distance is about four times greater than running the same distance. This difference is due to buoyancy compensation, overcoming the “drag” forces that impede body movement through the water and a lower mechanical efficiency in swimming as compared to other sports.
A modern racing bicycle with toe clips allows a cyclist to more easily expend the energy needed to power the cycle in a forward direction as compared to a swimmer swimming the crawl stroke. For the swimmer, considerable energy is necessary to bring each arm up, out of the water and back to the front position. Only during the underwater push phase of the crawl stroke is the body propelled forward.
Body Fat Helps with Female Swimmers’ Performance in the Water
Another interesting land vs. water comparison is that swimming performances of women are closer to that of men than in other sports. In fact, the first woman to swim the English Channel, Gertrude Ederle in 1926, beat the fastest men’s time by over two hours.
It’s important to remember that fat floats and muscle sinks. A higher percentage of body fat (typically seen in women) provides an improved hydrodynamic lift and easier flotation.
Fat distribution differences in women also make their legs float higher in the water. A greater fat content in the legs makes a swimmer’s flotation more horizontal while leaner legs tend to swing down in the water and increase body drag.
If you have aspirations to swim the English Channel, remember that a high level of body fat will also keep you cool in the icy water between Britain and France. Be sure to eat load up on carbohydrates prior to your swim, because the caloric cost of swimming the English Channel is about 5,200 calories (roughly twice that of running a marathon).
The Cool Temperature of Water Assists Some Exercisers
Some good news for swimmers is that the cool temperature of water greatly assists in keeping the body cool. Fever-level body temperatures during land exercise often result when excess body heat is not dissipated by the evaporation of sweat or wind convection. A high sweat rate and flushed red skin during land exercise often leads to heat cramps, heat exhaustion or even heat stroke.
Water moves heat away from the body faster than air. It therefore allows vigorous exercise without the risk of hyperthermia. Because the body’s sweat rate is also lower in the water, the danger of extreme dehydration is reduced.
Water Exercise Is Not Optimum for Weight Loss
Some bad news for swimmers is the cooling effect of the water is not beneficial for persons exercising for weight loss. Research into fat loss has shown swimming to be a less effective method of shedding fat than land exercise.
In fact, some swimming programs have caused some people to gain weight. Elevations in body heat during physical activity stimulate an important increase in metabolism within the muscles, enabling them to burn more calories.
After a strenuous workout on land, that body temperature may stay elevated up to six hours post-exercise, causing a significant “afterburn” of calories. However, this afterburn effect does not occur after swimming.
Many weight loss patients also comment that they are not overly hungry after a vigorous running or cycling workout, but they are starving after a swimming workout. This body response is likely due to the hypothalamus, which regulates both the body’s temperature and appetite.
It appears that when the hypothalamus is needed to control body temperature during physical exertion, it suppresses appetite afterwards. But when the hypothalamus is not needed to regulate temperature during exercise (such as during a swim in a pool), it seems to increase the appetite.
Water Exercise Is Good for Pregnant Women
While water exercise may not be the best for weight loss, it is excellent for exercise during pregnancy. For my master’s degree in exercise physiology at the University of North Carolina/Chapel Hill, my colleagues and I conducted a study examining the effects of a swimming program on pregnant women and their babies.
We tested female subjects during weeks 15, 25, and 35 of their pregnancy and also eight weeks after they gave birth. This study allowed us to evaluate exercise responses throughout advancing pregnancy and to compare them with the same person’s nonpregnant responses.
It was fascinating to see the heart rate response of the baby as the mother’s heart rate went up during exercise. The weight-supporting capacity of the water environment provided considerably less jarring to the abdominal region protecting the baby. Overall, a reduced heart rate and the cool water environment provides a safe workout environment for pregnant women.
Heart Rates Should Also Be Taken into Consideration
Land vs. water exercise differences also need to be taken into account when using “percent-of-max” training heart rates. Heart rates are generally about 12 to 18 beats per minute lower while someone is swimming than while running.
Swim coaches trying to regulate their team’s workouts based on exercise heart rate alone may inaccurately think their athletes are not working hard enough. For instance, one swim coach I consulted with pushed his team into overtraining because their exercise heart rates were lower than he expected. Their lower heart rates in the water were due to the hydrostatic pressure surrounding the swimmer’s body and the horizontal body position of swimming that increased blood flow back to the heart.
Because the heart has a greater “pre-load,” the heart doesn’t need to work as hard in the water to maintain the required blood circulation rate. This heart rate reduction in the water is an extremely important but overlooked parameter when determining how intense exercise should be based on heart rate and also in estimating the caloric burn of an exercise session.
Changing the Order of Events in Triathlons
Keeping heat dissipation in mind, I personally think the order of triathlon events should be changed. The traditional triathlon order of “swim – bike – run” order should possibly be changed to “swim – run – bike”.
A cyclist is much better able to handle the heat load of exercise as compared to a runner, due to a tremendous increase in convective heat loss. A cyclist riding at 20 miles per hour creates a breeze, which greatly enhances body cooling.
For my doctoral dissertation, I conducted a study at the University of Utah, which showed that a high wind speed enhances evaporative heat loss by enabling a greater percentage of the body’s sweat to evaporate. Sweat that simply drips to the ground only dehydrates the body but does not cool it.
I believe that swimming needs to remain the first triathlon event due to the danger of cramping up in the water after running or biking. However, switching the traditional triathlons to end in a cycling competition may greatly reduce the chance of heat-related illnesses during competition and also create faster triathlon times.
To Prepare for Triathlons, Spend Most of Your Time Running and Cycling
If you plan on training for a triathlon of any length this summer, I suggest spending a majority of your training time running and cycling, not swimming. It has been consistently proven that the best cyclists win triathlons because a good cyclist can gain several minutes (even hours) during the cycling split as compared to the few minutes lost during the swimming split.