Competitive swimmers in elite training programs have been challenged with high aerobic training volumes characterized in the literature as excessive, as a cause of depletion of energy reserves needed for non-oxidative energy production and detrimental to performances. Our hypothesis was that following a period of high volume training, a reduction in volume would result in recovery of non-oxidative energy production capacity as well significant improvement in swimming performance. Informed consent was obtained from a cohort of 12 female high school freshman swimmers (Mean+SE) age 13.9 +.7 yr. with a documented history of 3 years of training 315 + 23.5 min x wk-1 prior to initiating their first season of high volume training. Following 6 weeks of pre-season water and weight training the subjects initiated a water training program where the daily training volume was increased form 6 to 13 k x d-1 during a 6 week period with 11 to 13 k x d-1 being maintained for a peak training period (PT) of 10 weeks. PT was followed by 3-4 weeks of progressively decreased training (DETR). The swimmers' 50, 100 and 200 yard Freestyle best times were recorded from the previous season's best meet results and from meet results following DETR and transformed to average velocities per lap (m x sec-1). There were significant correlations between all velocity measurements which required the use of a Bonferonni correction factor of (.05/3) with a dependent sample t-test to determine if there were swimming performance improvements between PT and DETR. The Size Effect (ES) was calculated for the swimming performances to determine if the improvements were meaningful. Positive significant and meaningful differences were found for the 50 Free (PT 1.42 +.033 m x sec-1 and DETR 1.58 +.028 m x sec-1: p< .01, r=.930, rho=.977; ES >1), 100 Free (PT 1.37 +.028 m x sec-1 and DETR 1.47+.026 m x sec-1: p<01, r=.933, rho=.965; ES >1), 200 Free (PT 1.27 +.025 m x sec-1 and DETR 1.38 +.023 m x sec-1: p<.01, r=.74 rho=.60; ES >1) We concluded that this well prepared cohort (3 years of training 315 + 23.5 min x wk-1) significantly improved their swimming performances following DETR with meaningful ES in events which required both aerobic and non-oxidative energy production. Keyword(s): aquatics, exercise/fitness/physical activity, research