Direct measurement of physiologic thresholds based on respiratory gas exchange (RGE) or blood lactate [La] responses during incremental exercise is a standard technique with competitive athletes, serving to facilitate performance diagnostics and training prescription (Beneke and von Duvillard, 1996; Billat, 1996; Meyer, 2005). However, for the majority of exercise professionals and coaches working with other than elite athletes, direct measurement of physiologic thresholds is not practical. Less technical approaches, such as the Talk Test (Foster et al., 2008; 2009; 2012; Jeans et al., 2011; Recalde et al., 2002) and the Rating of Perceived Exertion (RPE) have been demonstrated to be of value relative to both performance diagnostics and prescription. There is a convincing body of evidence suggesting that the relative distribution of training intensity is regulated more effectively on the basis of the individual metabolic response to training (Billat et al., 1999; 2001; Esteve-Lanao et al., 2007; Seiler, 2010; Sjodin and Svedenhag, 1985; Steinacker, et al., 1998), than by the percent of maximal oxygen uptake (VO2max) or maximal heart rate (HRmax) concept that has been the dominant model in the fitness-rehabilitation community (Katch et al., 1978; Scharhag-Rosenberger et al., 2010). A variety of simple approaches might be of help in the case where RGE or [La] technology is not available. We have shown that the Talk Test response during incremental exercise testing was useful for prescribing absolute training intensities, both in sedentary (Foster et al., 2009) and well-trained/athletic (Foster et al., 2008; 2012; Jeans et al., 2011; Recalde et al., 2002) individuals. De Koning et al. (2012) observed that ventilatory (VT) and respiratory compensation thresholds (RCT) occurred at ~50 and ~75% of peak cycle power output (PPO), respectively. This finding is similar to observations of the percentages of maximal power output at the gas exchange threshold and critical power made by Burnley, Doust and Vanhatalo (2006) and Vanhatalo, Doust and Burnley (2008). Furthermore, Groslambert et al. (2004) demonstrated that a 30-min perceptive individual time trial allows a partial valid estimation of the power output at the anaerobic threshold in triathletes. These findings, and their implication relative to sustainable exercise, were anticipated a generation ago by Wasserman et al. (1967). Taken together, these findings suggest the question of whether absolute dimensions of exercise intensity (e.g. velocity or power output) available from an incremental exercise test, without RPE, gas exchange or [La] measurement, could be used to predict physiologic markers for guiding exercise training intensity. We already know that peak treadmill running velocity is, like V[O.sub.2]max and threshold measurements, a very good predictor of running performance (Noakes et al., 1985).
Accordingly, the purpose of this study was to determine if simple percentages of maximal incremental running velocity (Vmax), at which VT and RCT occur, could be used to define training intensity criteria. If successful, we would be able to provide, to a broader range of athletes and to professionals responsible for the conditioning of athletes, a simple and inexpensive technique to define desired training intensities based only on Vmax data.
Experimental approach to the problem
This study was conducted in two phases. Phase 1 was designed to evaluate physiologic thresholds (VT and RCT) as percentages of Vmax during an incremental treadmill running test. Afterward Phase 2 was designed to cross-validate the percentages of Vmax suggested based on the results obtained during Phase 1.
The subjects provided written informed consent to the procedures and the protocol was approved by the University human subjects committee. The protocol conformed to the broad principles of the Declaration of Helsinki.
Thirty-one well-trained athletes were recruited to participate in Phase 1. They represented a variety of type and level of athletic accomplishment, including University level runners, soccer players, and basketball players as well as regularly competing recreational runners. Twenty well-trained athletes with similar demographics (Table 1) were recruited to participate in Phase 2. None of the subjects of Phase 1 participated to Phase 2. All subjects were training [greater than or equal to] 5 hrweek-1 at the time of study.
During Phase 1, each subject performed a maximal incremental treadmill test (1% grade, start @ 1.56 m x [s.sup.-1] for 3 min + 0.22 m x [s.sup.-1] every minute), with measurement of respiratory gas exchange using open circuit spirometry (Parvo Medics, TrueOne 2400 Metabolic Measurement System, Sandy, UT). Measurements were made using a mixing chamber based system, with data integration every 30 s. In stages where the last full minute was not completed, Vmax was interpolated based on proportional time in stage. VT and RCT were determined by visual inspection of the v-slope and ventilatory equivalent for each individual test (Foster and Cotter, 2006). Consequently, the running speed at the determined VT and RCT was identified.
During Phase 2, each subject performed the identical treadmill test as in Phase 1 in order to determine Vmax, although without measurement of respiratory gas exchange. They then performed two steady-state sub-maximal running bouts on the treadmill, designed to be 30 min in duration, at intensities (64% and 86% Vmax) which were predicted to require [less than or equal to] VT and [greater than or equal to] RCT (based on the results of Phase 1). [La] was measured at 10...