This phenomenon is known in multisport as "jelly legs". Athletes experience a sensation where their legs are not in pain or cramping, but they stumble as if walking on soft jelly. First-time aquathlon participants are often surprised and mentally unprepared for this sensation.

During swimming, the body prioritizes blood flow to the upper body and arms to maintain propulsion through the water. The legs primarily provide light kicks for balance, not primary propulsion. When athletes exit the water and start running, leg muscles suddenly become the primary movers, but blood flow has not yet sufficiently redistributed. For the first 30-60 seconds, leg muscles operate with less oxygen than needed. This results in legs feeling soft, heavy, and hard to control during the swim-to-run transition (T1).

National athlete Vu Dinh Duan competes at Aquaman Vietnam 2024. Photo: VnExpress Marathon

Experienced aquathlon or triathlon athletes are less prone to jelly legs, as their bodies have learned to coordinate between the two disciplines through repeated training. For newcomers, the neuromuscular system lacks this reflex. Each transition presents an unfamiliar situation for the brain. Additionally, high-intensity swimming with poor breath control towards the end of the segment can deplete glycogen in the leg muscles earlier, worsening the feeling of weakness.

4 ways to prevent jelly legs

Athletes should proactively reduce the risk of leg numbness while still in the water. In the final 200m of the swim, athletes should switch from light kicking to strong, continuous kicks. This action activates the leg muscles earlier, helping blood flow to the lower limbs before the body exits the water. Runners do not need to sustain this intensity for long; 30 to 45 seconds is sufficient to make a noticeable difference when getting out of the water.

Another tip is for athletes to exit the water properly. The most common mistake in T1 is to immediately start running after exiting the water. Instead, athletes should walk for two to three steps to allow their circulatory system to stabilize. Avoid bending down suddenly to grab a cap or shoes, as rapid bending can worsen feelings of imbalance.

The first 500m of the run is a time for control, not for sprinting. Even if legs feel more stable after T1, the body still needs more time to fully adapt. Athletes should run about 15-20 seconds slower than their target pace per kilometer for the initial 500m to prevent a sudden spike in heart rate and early leg muscle cramps. The numbing sensation typically lessens significantly after about 800m to one kilometer. After this, athletes can increase their pace.

Athletes can also train their brain to adapt to jelly legs through brick workouts (swimming immediately followed by running). Just two to three brick sessions before race day are sufficient for the neuromuscular system to learn faster coordination between the two disciplines. Athletes do not need to train at high intensity; it is important to accurately simulate the transition sequence for the brain to build the reflex.

Minh Khang

Hoiana Aquaman Vietnam 2026 takes place on 26/7 at Hoiana Resort & Golf, Da Nang. This is Vietnam's first swim-run duathlon event, organized since 2022. The event features various distances, including: Sprint Aqua, Aqua Kid, Flash Aqua, Rush Aqua, Half Aqua, and Aquaman individual or relay. Registration for the event is currently open; interested athletes can register here.