EXERCISE INTENSITY-DEPENDENT INHIBITION OF 1-METHYL-1-NITROSOUREA INDUCED MAMMARY CARCINOGENESIS IN FEMALE F344 RATS

The objective of this experiment was to evaluate the effects of treadm ill exercise on tumor induction in an experimental model for breast ca ncer, Female F-344 rats were injected i.p. with 50 mg MNU/kg body wt a t 50 and 57 days of age, Animals were assigned to one of five groups: sham exercise or 35% or 70% maximal treadmill running intensity for 20 or 40 min/day, 5 days per week, These work rates represent an exercis e intensity level generally considered insufficient to improve cardiov ascular fitness (35% maximal intensity) or an aerobic level of exercis e sufficient to improve cardiovascular fitness in humans (70% maximal intensity). Rats were exercised for 3 months following carcinogen admi nistration at which time the experiment was terminated. Mammary cancer incidence was reduced by as much as 37% and cancer multiplicity by < 60% at the highest exercise intensity, Unexpectedly, the degree of pro tection against cancer was proportional to the intensity but not to th e duration of exercise.