The effectiveness of creatine is now accepted beyond doubt. Countless studies have shown that it is an effective supplement for improving lean muscle mass, increasing strength and increasing high intensity (anaerobic) exercise capacity. It is accepted by the International Society of Sports Nutrition (ISSN) and the American College of Sports Medicine as an effective ergogenic aid which performs as claimed. The ISSN states that creatine is "the most effective nutritional supplement currently available in terms of improving lean body mass and anaerobic capacity".
So the argument has moved on from whether creatine works, or not, to the best way to take it. Various dosing protocols exist. Probably the most widely used protocol with the most evidence backing it up is to consume a loading dose of 20g/day for 5 - 7 days followed by a maintenance dose of 3 - 5g/day. This protocol has been shown to maximally increase muscle creatine stores in a number of studies.
But can taking creatine only occasionally also produce results? What about taking it only on training days? A new study published in the Journal of Strength and Conditioning Research seems to suggest that the answer is yes!
In this new study two groups of resistance training adults were given approximately 10 grams per day of creatine on training days only (5g consumed before training and 5g consumed after). One group trained 3 days a week and the other group trained 2 days a week. Both groups were compared to similar groups consuming a placebo instead of creatine.
At the end of the study both the creatine groups had significantly greater increases in muscle thickness than the placebo groups, but did not show any difference between the 2 day a week group or the 3 day a week group.
This is good news for those who are forgetful or just don't like taking creatine everyday. Although you won't get the same benefits as taking it every day, you will gain more muscle from just taking it on training days.
Candow DG, Chilibeck PD et al. Effect of different frequencies of creatine supplementation on muscle size and strength in young adults. J Strength Cond Res. 2011 Jul;25(7):1831-8.