By the time you feel thirsty, your performance has usually already started to drop. Thirst lags behind what's actually happening in your body.
The 2% line
Losing around 2% of your body weight in fluid (about 1.4kg for a 70kg athlete) is enough to measurably hurt performance. On a summer ride through the Magaliesberg or a humid Durban run, that can happen in well under two hours.
What slips first
- Aerobic capacity – the same pace costs more
- Muscular endurance
- Reaction time and coordination
- Decision-making, which matters a lot in team sports
Know your sweat rate
Weigh yourself before and after a typical session (without clothes, after towelling off). Every 1kg lost is roughly 1 litre of sweat. Add what you drank during the session and you have a good estimate of your hourly sweat rate.
Water alone isn't enough
Sweat contains sodium, and some athletes lose 2–3 times more per litre than others. Drinking fluids with sodium helps your body absorb and keep that fluid, instead of just passing it through.
Adjust for the conditions
Your needs change with the season. A Highveld winter morning and a Lowveld summer afternoon call for very different plans, so review your hydration as the weather changes.
Add GO Hydro tablets to your bottle for electrolytes without extra calories, or use electrolyte drinks on longer sessions.
Adapted from Science in Sport research content for South African athletes.
