Energy system contribution to 2000 m rowing ergometry using the accumulate oxygen deficit

Abstract

Exercise scientists and coaches frequently base physical conditioning objectives on the nature and magnitude of the physiological demands imposed by competitive events. Part of this demand may be characterized by the extent and proportion of aerobic and anaerobic energy supply associated with performing an athletic task. Maximum effort rowing imposes severe physiological demands owing to high force application per stroke, extensive skeletal muscle involvement, and repetition of a unique movement pattern, distinguishing it somewhat from other endurance exercise modalities. Rowing ergometry represents a valid and reliable simulation of the biomechanical and physiological demands of on-water rowing, and the 2000 m rowing ergometer time trial has become a standard physical performance test for rowers. However, empirical information regarding proportional aerobic and anaerobic energy supply during maximum effort 2000 m rowing is scarce. Studies which have investigated the theme report a proportional dominance (70-90%) by aerobic energy supply, but the research studies are limited in number and dissimilar in methodology. Further, models of relative energy system contribution popularized in traditional textbooks frequently do not mirror the results of these studies. The accumulated oxygen (O2) deficit (AOD) method, despite limitations, remains a preferred method for differentiating aerobic and anaerobic energy supply during dynamic, whole-body exercise in athletes, yet few AOD measurements have been made on rowers during 2000 m rowing ergometer time trials. Also, while several anthropometric and physiological characteristics have long been shown to be associated with rowing performance, relationships between energy system contributions and performance do not appear to have been investigated to date. The purpose of this study was to quantify the relative energy system contributions during a maximum effort 2000 m rowing ergometer time trial, and to determine the correlations between performance and measures of aerobic and anaerobic energy supply. A quantitative, cross-sectional research study was designed to obtain descriptive and correlational data from a sample of elite oarsmen during a single observation period. Twentyfive national and international level male rowers (mean ± standard deviation [SD] age: 21.0 ± 3.6 years, rowing training history: 5.7 ± 3.4 years, maximum O2 uptake [VO2max]: 4.64 ± 0.54 L·min-1 or 58.9 ± 5.3 ml·kg-1·min-1) from the South African national rowing squad volunteered as participants. In the first of two separate test sessions within a period spanning no more than five days, participants underwent anthropometric assessment (body mass: 78.9 ± 7.6 kg, stature: 185.2 ± 5.5 cm, sum-of-seven skinfolds: 53.6 ± 9.8 mm) and completed a 2000 m time trial (performance time: 405.6 ± 20.5 s, range: 373.0-452.0 s) on a Concept II rowing ergometer. The second session involved an incremental rowing ergometer exercise test including five or six submaximal intensity stages spanning the range 35-85% of time trial average power output, and a maximum effort stage to determine peak power output and VO2max. Pulmonary O2 uptake (VO2) was recorded continuously during exercise via open-circuit spirometry. Aerobic energy supply was determined from accumulated O2 uptake during the time trial, while anaerobic energy supply was calculated from the AOD. Specifically, incremental exercise test data was used to establish the VO2-power output relationship (R2: 0.995 ± 0.004, SEE: 0.061 ± 0.028 L·min-1) for each participant, which was solved for average power output to yield the total equivalent O2 demand of the 2000 m time trial. The difference between accumulated O2 uptake and total equivalent O2 demand represented the AOD. Descriptive statistics were used to report physiological responses and measures of aerobic and anaerobic energy supply, while Spearman rank order correlation coefficients (rho) were calculated to evaluate the relationships between energy system measures and 2000 m time trial performance. The principal finding of this study was in agreement with earlier research reports that aerobic and anaerobic energy supply respectively represented 80-82% (range: 73-93%) and 18-20% (range: 7-27%) of total energy cost during a maximum effort 2000 m rowing ergometer time trial. Notably, relative energy system contribution showed considerable variation among participants which could not be fully explained by differences in exercise duration, since the correlations between time trial performance and energy system fractional contributions, while significant (P < 0.05), were not strong (rho: 0.5-0.6). While significant relationships were also found between 2000 m performance time and age, rowing training history, body mass, stature, accumulated O2 uptake and AOD, only VO2max and peak VO2 (VO2peak) expressed in absolute terms, peak power output, and total equivalent O2 demand demonstrated strong (rho: 0.82-0.96) correlations with 2000 m rowing ergometer performance time. Aerobic energy supply dominates total energy provision during a maximum effort 2000 m rowing ergometer time trial, with VO2 reaching rates exceeding 97% of VO2max. However, AOD values recorded in this study (6.10 L O2 eq or 76.9 ml O2 eq·kg-1) support the argument that 2000 m rowing involves extensive utilization of anaerobic capacity. So while aerobic energy supply dominates proportionally, the absolute values of aerobic and anaerobic energy supply reported here underscore the large cumulative energy demand imposed by a 2000 m rowing ergometer time trial. Significant relationships commonly observed between rowing performance and rower characteristics, including measures of body size and endurance fitness, were corroborated by this study. However, the ability to produce and sustain a high power output during rowing, necessarily supported by the capacity for high absolute rates of both aerobic and anaerobic energy supply regardless of their respective contributions was the bioenergetic capability most strongly related to performance in a 2000 m rowing ergometer time trial in this study. Improved understanding of aerobic and anaerobic energy supply during simulated rowing races such as the 2000 m rowing ergometer time trial has practical utility for exercise scientists and coaches in terms of rower identification and management, as well as in the planning, regulating and monitoring of rowing training programmes. Future investigations should consider assessing seasonal changes in the relative energy system contributions for a 2000 m rowing ergometer time trial, and distribution of aerobic and anaerobic energy supply in relation to the regulation of power output (pacing) during simulated rowing races.