Caffeine

Caffeine is a stimulant found in coffee, tea, soft drinks and chocolate that can improve performance in both endurance and strength athletes.^{1Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 260.} Taken about an hour before or during prolonged exercise, it lowers perceived exertion, improves work capacity and raises alertness.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.} In early cycling research at 80% of maximal oxygen uptake, time to exhaustion rose from 75 to 96 minutes.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.} Evidence for sprint and power work is less clear, though caffeine can improve strength and muscular endurance in resistance training.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.},^{3Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 157.}

In practice

• Research doesn’t support caffeine causing diuresis during exercise or harmful changes in fluid balance.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.}
• Side effects include anxiety, stomach upset, restlessness, insomnia, tremors and heart arrhythmias, with greater risk above 9 mg/kg.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.} Stopping can cause headache and fatigue.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.}
• The IPTA textbook reports the FDA’s 400 mg daily safety level for the general population and advises against use by clients taking stimulant medications, anticoagulants, MAO inhibitors or quinolone antibiotics.^{4International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 543.}
• Tolerance develops quickly and can blunt the performance benefit, more for endurance than for lifting.^{5Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 158.} Cutting caffeine later in the day helps protect sleep.^{6Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 159.}
• Evidence that caffeine causes fat loss or curbs appetite is inconsistent.^{5Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 158.}

Performance doses by source

The NSCA gives a range of 3 to 9 mg/kg, with no additional benefit above it.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.} IPTA recommends 3 to 6 mg/kg about 60 minutes before exercise.^{4International Personal Trainer Academy, Certified Personal Trainer Textbook, p. 543.} Helms and colleagues use 4 to 6 mg/kg for performance, or 1 to 3 mg/kg a day to fight tiredness.^{3Helms et al., The Muscle & Strength Pyramid: Nutrition, 2nd ed., p. 157.} The NSCA also notes that coffee may help endurance less than caffeine tablets.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 261.}