There is a growing body of research supporting the benefits of plyometrics for endurance athletes. The most recent is a study out of New Zealand using cyclists as subjects (Paton, 2005, Combining explosive and high-resistance training improves performance in competitive cyclists, J Strength Cond Res 19(4): 826-30). In this study nine well-trained riders did three, thirty-minute workouts weekly for four weeks. Each workout consisted of alternating three sets of explosive jumps with three sets of high-resistance bike sprints (5 x 30 sec @ 60-70 rpm with 30 sec recoveries). After 12 weeks the experimental group improved their 1km power by 8.7%, their 4km power by 8.1%, peak power by 6.8% and their LT power by 3.7%. These are huge changes in performance for only 12 sessions especially given that the riders were already well-trained. The total oxygen cost of these power tests decreased by 3% indicating greater economy. There was no significant change in the control group.
An Australian study done with runners using only plyometrics and not resisted running as in the above cycling research showed benefits also but to a lesser degree (Spurrs, 2003, The effect of plyometric training on distance running performance, Eur J Appl Physiol 89(1): 1-7). The well-trained group of runners improved their 3km race time, on average, by only 2.7%. But then this study only lasted for six weeks and did not include resisted running in a manner similar to what the cyclists did in the above.
This winter I am using combined plyometric and resisted high-intensity exercise with the triathletes and road cyclists I coach. After a few weeks of preparation in which they followed the weight training program described in my Training Bible books culminating with the MS phase, they embarked on a program of two or three such plyo-sprint sessions weekly for four to six weeks (8-12 sessions total). Each session took about 30 minutes and included three sets of 10-20 box jumps (see picture) alternated with three sets of five of either resisted, 20-30 second sprints as in the first paragraph (cyclists) or 20-30 second treadmill sprints at a 5% grade (runners). The intensity was to feel like a 9 on a 10-point effort scale.
I reduced the number of sessions per week and the length of the high-intensity efforts for those who I felt were at high risk for injury. But even in doing that one of the runners slightly strained a hamstring (fortunately, it healed quickly) and I terminated the series of workouts early for another runner who strained a calf in other training. Since none of the others have completed the series of workouts yet or been retested, I don't have anything to report. All have reported feeling like the workouts were beneficial. Time will tell, but I believe we will see significant improvement.