This study examined the effects of two distinct phases of endurance training (summer and in-season training) in previously well-trained male and female high school cross-country runners. Eleven males and 11 females from the same high school training program were recruited for the three testing sessions: post-track season (June), postsummer training (mid-August), and post-cross-country season (early-November). However, due to injury and other circumstances, only 10 males and 4 females completed all testing sessions. Thus, baseline characteristics were analyzed for both genders; however, longitudinal analysis was only conducted using the males. Submaximal measurements included running economy (RE), blood lactate concentration ([BLa]), and heart rate (HR) at three running speeds in females (6, 7, and 8 mph), and males (7, 8, and 9 mph). Maximal measurements of oxygen uptake (VO2max) and HR, neuromuscular characteristics of isokinetic knee extension strength and vertical jump height, and body composition were also measured. Baseline results showed that the males possessed a higher VO2max, greater neuromuscular characteristics, and lower submaximal [BLa] and HR values than the females. Longitudinal analysis of the males showed that there was an increased VO2max, decreased maximal HR, and decreased neuromuscular strength following summer training. In-season training precipitated further increases in VO2max, an increase in maximal and submaximal HR, and increased neuromuscular characteristics. RE and [BLa] did not significantly change (p<_ 0.05) throughout the course of the study. Likely, it is the subtle changes in these variables in previously welltrained runners which account for the slower performance times at the beginning of the cross-country season and the improvements thereafter. / School of Physical Education

This study evaluated the training adaptations in female adolescent cross-country runners over two training seasons. Although the effects of endurance training in this population are understood, the specific adaptations resulting from pre-season and in-season training are not clear. The physiological changes occurring over these two training seasons in 10 female runners (15.7 ± 0.8 yrs, 165.6 ± 5.6 cm, 53.8 ± 6.1 kg) were assessed. Maximal exercise responses were measured during a continuous graded exercise test and submaximal exercise responses were quantified at 7 and 8 mph. Isokinetic muscle strength was assessed at four movement speeds (60-240°/sec) and muscle power was calculated using vertical jump height. Body composition also was assessed. HR at maximal and submaximal exercise declined during pre-season training and then increased during in-season training. Blood lactate [BLa] measurements at 7 and 8 mph decreased following summer training. Whole body bone mineral content (BMC) and bone mineral density, and femoral head BMC increased. In conclusion, it appears that high volume, low intensity training lowers [BLa] with no corresponding change in oxygen utilization in highly trained female adolescents. Running also appears to have a positive impact on bone mass in female adolescents. / School of Physical Education, Sport, and Exercise Science