Supplements

Only a handful of supplements have solid evidence for performance; most others show little or no effect.

• Caffeine: about 3 mg per kg, 30 to 60 minutes before; improves endurance.
• Beetroot juice (nitrate): a concentrated shot 2 to 3 hours before; may help efforts of a few minutes to half an hour, less in well-trained runners.
• Creatine: mainly helps sprints, repeated efforts and strength; it adds 1 to 2 kg of water weight.
• Beta-alanine: may help hard efforts of 1 to 4 minutes; a harmless tingling is common.
• Iron, vitamin D or other vitamins only help if you are low: a blood test tells you.

Supplements are loosely regulated: choose third-party tested products and check with a doctor or sports dietitian first.