The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers

RESEARCH ARTICLE The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers Chul-Ho Kim1*, Courtney M. Wheatley1☯, Mehrdad Behnia2☯, Bruce D. Johnson1☯ 1 Human Integrative and Environmental Physiology Laboratory, Mayo Clinic, Rochester, Minnesota, United States of America, 2 Cardiopulmonary Laboratory, Doctors Hospital, Augusta, Georgia, United States of America ☯ These authors contributed equally to this work. * a11111 Abstract OPEN ACCESS Citation: Kim C-H, Wheatley CM, Behnia M, Johnson BD (2016) The Effect of Aging on Relationships between Lean Body Mass and VO2max in Rowers. PLoS ONE 11(8): e0160275. doi:10.1371/ journal.pone.0160275 Editor: Massimo Sacchetti, University of Rome Foro Italico, ITALY Received: February 23, 2016 Accepted: July 15, 2016 Published: August 1, 2016 Copyright: © 2016 Kim et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: Participants did not consent to sharing data publicly and the institutions involved feel that it may be possible for individuals to uniquely identify subjects based on some of the physiological and anthropometric data if provided in a raw format. Thus the only clean way to do this is through averaged values as presented in the manuscript. Funding: Doctors Hospital, Augusta, GA, funded the present study. Competing Interests: The authors have declared that no competing interests exist. Aging is associated with a fall in maximal aerobic capacity as well as with a decline in lean body mass. The purpose of the study was to investigate the influence of aging on the relationship between aerobic capacity and lean body mass in subjects that chronically train both their upper and lower bodies. Eleven older rowers (58±5 yrs) and 11 younger rowers (27±4 yrs) participated in the study. Prior to the VO2max testing, subjects underwent a dual energy X-ray absorptiometry scan to estimate total lean body mass. Subsequently, VO2max was quantified during a maximal exercise test on a rowing ergometer as well as a semi-recumbent cycle ergometer. The test protocol included a pre-exercise stage followed by incremental exercise until VO2max was reached. The order of exercise modes was randomized and there was a wash-out period between the two tests. Oxygen uptake was obtained via a breath-by-breath metabolic cart (Vmax™ Encore, San Diego, CA). Rowing VO2max was higher than cycling VO2max in both groups (p<0.05). Older subjects had less of an increase in VO2max from cycling to rowing (p<0.05). There was a significant relationship between muscle mass and VO2max for both groups (p<0.05). After correcting for muscle mass, the difference in cycling VO2max between groups disappeared (p>0.05), however, older subjects still demonstrated a lower rowing VO2max relative to younger subjects (p<0.05). Muscle mass is associated with the VO2max obtained, however, it appears that VO2max in older subjects may be less influenced by muscle mass than in younger subjects. Introduction Maximal oxygen consumption (VO2max) is the maximum capacity to transport and utilize oxygen and is often used as a measure of an individual’s aerobic capacity. Generally, VO2max decreases gradually with advancing age, and the rate of decline is approximately 10% per decade after the age of 25 years, and more specifically was suggested to be 15% between the ages of 50 and 75 [1, 2, 3]. In addition, a previous meta-analysis illustrated that age-related declines in VO2max were approximately 0.40, 0.39 and 0.46 ml/kg/min per year for sedentary, PLOS ONE | DOI:10.1371/journal.pone.0160275 August 1, 2016 1 / 11 Skeletal Muscle Mass and Aerobic Capacity active and trained males respectively and 0.35, 0.44, 0.62 ml/kg/min per year for sedentary, active and trained female respectively [4, 5, 6]. Age-related decline in VO2max results from multiple factors: decreased maximal heart rate and stroke volume, reductions in blood volume due to pooling from less effective muscle pump action of the valves in the extremities, and stiffening of both the heart muscle fibers and thickening and stiffening of the arterial walls, reduced peripheral oxygen extraction and maximal A-V O2 difference [7, 8, 9, 10]. Age-related muscle loss (sarcopenia) also appears to play an important role in the decline in VO2max; by the age of 50 about 10% of muscle area is lost and this rate only increases in the decades that follow. In concert with sarcopenia, muscle strength declines by 15% per decade in the 60s and 70s and doubles to 30% after 80 [11]. A previous study by Fleg and Lakatta (1988) demonstrated that whole body lean mass contributed to a decline in VO2max with advancing age in sedentary individuals [12]. Similar results were observed in active individuals [13, 14]. However, active individuals demonstrated a slower rate of decline than sedentary individuals [3, 15]. Thus the influence of muscle mass on VO2max can be influenced by training and possibly type of training (e.g., upper vs lower extremity exercise) as well as other factors, such as how muscle mass is quantified (e.g., only active muscles vs total lean body or skeletal muscle mass) [13]. Rowing is a demanding sport requiring a high aerobic capacity and the ability to sprint; yet it is a common sport amongst older individuals. It is an activity requiring large muscle mass and the ability to distribute blood flow to both upper and lower extremity skeletal muscles simultaneously. Accordingly, rowers exhibit both upper and lower body muscle adaptations, and thus offer a unique population to better understand the effect of muscle mass on VO2max. The purpose of study was to investigate the relationship between active muscle mass and VO2max, and how this relationship might be influenced by age. Two separate exercise modes– recumbent cycling (targeting leg muscles only) and rowing (targeting leg and upper body muscles)–were utilized to differentiate active muscle mass. A mode specific VO2max was quantified based on active muscle for a group of younger and older rowers. Methods For the present study, 22 subjects were recruited from rowing teams in Augusta, Georgia (GA). Eleven older subjects (age = 58±5 yr, 6 males and 5 females) and 11 younger subjects (age = 27±4 yr, 6 males and 5 females) who had at least a one year of competitive rowing experience, a current baseline level of training that included rowing and typical synergistic activities–running, swimming, resistive training and etc. They performed for a minimum of one hr four times a week, and were planning to participate in seasonal rowing competitions– regattas. Subjects who had a body mass index (BMI) >30, a history of cardiovascular or pulmonary disease, an inability to perform repeated volitional level of exercise or females who were pregnant were exc (...truncated)