I've been using Sportlegs for many years now as a serious endurance road cyclist decidedly "up in age"! I typically ride 6,000 m or more in a season, usually with only light riding in December and February to give my body a break. Sportlegs is a fantastic supplement for any time I know I will be doing a tough ride that involves speed work, tough climbs or interval training, century rides and "big" rides in hot temperatures with high humidity and Dew Point degrees. My legs don't cramp at inconvenient times, nor are they anywhere near a fatigued as they can get if I don't use Sportlegs. I believe in this MK 677 and feel it helps me keep an edge as I've aged. Highly recommended