This is an excerpt from Designing Resistance Training Programs-4th by Steven J. FleckW & illiam J. Kraemer.
Yes they can, especially when the exercise volume increases dramatically to the point at which performance gains due to an off-season training program are lost. This is what happened to a group of National Collegiate Athletic Association Division I American football players in the off-season and spring practice program (Moore and Fry 2007).
For football players, year-round training is broken up into training phases (e.g., fall in-season, winter off-season, spring football, and summer preseason). Starting with the winter off-season program, players performed only a linear periodized heavy resistance training program during the first month of winter conditioning. In the following month a high-volume sport conditioning program (e.g., sprints, agility drills) was added to the strength training program. This was followed over the next month by the typical 15 spring football practices. After the first month, all of the 1RM strength tests showed improvement. Then, after the second month of performing heavy resistance training and conditioning drills, maximal squat and power clean 1RMs decreased, returning players to pre-first-month levels. By the end of the 15 football practice sessions, even upper-body bench press 1RMs had returned to pre-first-month levels. Speed and agility along with vertical jump improved after the first month and then remained unchanged for the rest of the winter program.
One might speculate that dramatically reducing the volume of resistance training while focusing on maintaining intensity might be a plausible approach for eliminating the loss of strength and power when conditioning and sport practices occur concurrently. Additionally, as pointed out in the study, more communication is needed between the strength and conditioning and sport coaches. Program modifications and careful monitoring are necessary when total exercise volume is dramatically increased in a training cycle.
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