title: Time course and mechanisms of adaptations in cardiorespiratory fitness with endurance training in older and young men.
abstract: The time-course and mechanisms of adaptation of cardiorespiratory fitness were examined in 8 older (O) (68 +/- 7 yr old) and 8 young (Y) (23 +/- 5 yr old) men pretraining and at 3, 6, 9, and 12 wk of training. Training was performed on a cycle ergometer three times per week for 45 min at approximately 70% of maximal oxygen uptake (Vo(2 max)). Vo(2 max) increased within 3 wk with further increases observed posttraining in both O (+31%) and Y (+18%), (P < 0.05). Maximal cardiac output (Q(max), open-circuit acetylene) and stroke volume were higher in O and Y after 3 wk with further increases after 9 wk of training (P < 0.05). Maximal arterial-venous oxygen difference (a-vO(2 diff)) was higher at weeks 3 and 6 and posttraining compared with pretraining in O and Y (P < 0.05). In O, approximately 69% of the increase in Vo(2 max) from pre- to posttraining was explained by an increased Q(max) with the remaining approximately 31% explained by a widened a-vO(2 diff). This proportion of Q and a-vO(2 diff) contributions to the increase in Vo(2 max) was consistent throughout testing in O. In Y, 56% of the pre- to posttraining increase in Vo(2 max) was attributed to a greater Q(max) and 44% to a widened a-vO(2 diff). Early adaptations (first 3 wk) mainly relied on a widened maximal a-vO(2 diff) (approximately 66%) whereas further increases in Vo(2 max) were exclusively explained by a greater Q(max). In conclusion, with short-term training O and Y significantly increased their Vo(2 max); however, the proportion of Vo(2 max) increase explained by Q(max) and maximal a-vO(2 diff) throughout training showed a different pattern by age group.
authors.affiliation: Canadian Centre for Activity and Aging, School of Kinesiology, The University of Western Ontario, London, Ontario, Canada.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Murias
authors.forename: John M
authors.initials: JM
authors.lastname: Kowalchuk
authors.forename: Donald H
authors.initials: DH
authors.lastname: Paterson
mesh_terms: D000222:Adaptation, Physiological; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D001642:Bicycling; D002302:Cardiac Output; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply / Q000378:metabolism*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption; D010807:Physical Endurance; D013318:Stroke Volume; D013997:Time Factors; D055815:Young Adult
chemical_list: D010100:Oxygen