Effects of chronic, moderate endurance running on body composition and cardiac structure in women

The effects of chronic endurance running on cardiac structure and function were studied in 12 young women. Initially subjects ran 15.9 ± 3.9 miles/week (mean ± SD); distance was increased without regard to speed. When running distance had increased by 30 miles/week (±30) to 46.2 ± 4.2 miles/week, resting heart rate decreased from 65.3 ± 14.0 to 58.4 ± 10.5 beats/min (P < .05), submaximal heart rate decreased from 170.0 ± 6.2 to 157.6 ± 11.1 beats/min (P < .05), treadmill duration increased from 10.8 ± 0.8 to 11.8 ± 1.0 min (P < .05), and lean body weight increased from 41.5 ± 1.3 to 42.5 ± 4.1 kg (P < .05). When running distance had increased by 50 miles/week (±50) to 62.0 ± 8.4 miles/week, resting heart rate decreased to 57.5 ± 12.4 beats/min (P < .05), submaximal heart rate decreased to 148.4 ± 11.7 beats/min (P < .02), treadmill duration time increased to 12.0 ± 1.1 min (P < .05), and lean body weight increased to 43.5 ± 1.4 kg (P < .001). Maximal oxygen uptake and maximal heart rate did not change. Serial M-mode echocardiographic measurements of left ventricular chamber size, wall thickness, and calculated left ventricular mass were not different than a reference group matched by age and sex and did not change at Δ30 or Δ50. Thus, moderate endurance running in women resulted in decreased resting and submaximal heart rate, increased treadmill endurance, and increased lean body weight. These changes indicative of a training effect occurred without primary alterations in cardiac dimensions.