Many people swim for fitness, hopping in the pool and performing a straight, relaxing long-duration workout. This low impact aerobic movement enhances cardiovascular strength, but does swimming build muscle?
Muscle is a soft tissue in the human body which consumes more energy than other tissues, making it essential for weight loss. Muscle also plays a vital role as we age, helping pull on the bone via the tendon, creating bone turnover and prevention of osteoporosis. Moreover, muscle helps function and plays a role in fall prevention. These roles make building muscle vital and understanding if swimming builds muscle key, especially if it is your only form of exercise is swimming.
Three mechanisms result in building muscle:
Mechanical tension: Mechanical tension is typically described as muscle feeling like the muscle it is going to rip off the bone. Different types of tension do exist:
“[i]f you place tension on a muscle by stretching it passively (without letting it contract), the source of tension is called passive elastic tension. If you place tension on a muscle by flexing it as hard as possible via an isometric contraction, the source of tension is known as active tension (Contreras 2013)”. Swimming, like all dynamic activities, causes passive and active elastic tension. In swimming, the mechanical tension is relatively low during a casual swim. However, swimming sprints increases the passive and active tension.
- Metabolic stress: Imagine performing 10 x 100 - yard sprints for time on 2:00. Think of the feeling of your arms, as bricks and your stomach turning … this is metabolic stress. Tenured swimmers know this feeling and type of set all too well. However, the causal swimmer (even Masters swimmer) may not know this set or sensation, as straight aerobic swimming is the common practice. Metabolic stress is also aided by hypoxia, the lack of oxygen supplied to the muscle. Swimming is rare as it uses periods of hypoxia and hypercapnia. Metabolic stress is likely high in swimming, due to the hypoxic nature combined with interval or lactate tolerance sets (like 10 x 100s).
- Muscular damage. Delayed onset muscle soreness (DOMS) typically peaks 48 hours after exercise. Eccentric muscular activation, rapid elongation of the muscle, is the main culprit culprit of DOMS. Muscle damage is also spiked by exercise novelty, one reason why one is more sore at the beginning of the season or when they do a new dry-land activity. Novelty is important for building muscle size, a uncommon process in swimming. However, novelty is possible through different drills, strokes, and equipment in the pool. One example of using equipment for building muscle is the use of fins, paddles, of resistance swimming racks. All of these tools provide subtle novelty to swimming, encouraging muscle growth.
Swimming causes stress in these three categories, but certain forms of training elicit greater stress for building muscle. If you are seeking maximal muscle growth in swimming, repeated sprints of at least 20 maximally stresses the metabolic system, creating high mechanical tension (for swimming), and causing muscular damage (especially if you don't do this exercise often or use a novel piece of equipment). Most swimmers do not necessarily need to build more muscle, instead they need to improve their swimming biomechanics for higher velocity. However, if you are seeking more muscle, keep these mechanisms of building muscle in mind as you pick your swimming sets, especially if you don't perform resistance training, the ultimate muscle builder.