Scand J Med Sci Sports 2006: 16: 27–34 Printed in Singapore . All rights reserved DOI: 10.1111/j.1600-0838.2004.00424.x
COPYRIGHT & BLACKWELL MUNKSGAARD 2004
Predictive validity of ventilatory and lactate thresholds for cycling time trial performance Markus Amann1,2, Andrew W. Subudhi1,2, Carl Foster3 1
The Orthopedic Specialty Hospital, Salt Lake City, UT, USA, 2University of Utah, Salt Lake City, UT, USA, 3University of Wisconsin, La Crosse, WI, USA
Corresponding author: Markus Amann, PhD, Room 4245, Medical Sciences Center, 1300 University Avenue, Madison, WI 53706-1532, USA. Tel: 11 608 262 9499, E-mail:
[email protected] Accepted for publication 16 July 2004
Purpose: To determine which laboratory measurement best predicts 40 km cycling time-trial (TT) performance. Methods: Fifteen male cyclists performed lactate-threshold (LT), ventilatory-threshold (VT), 5 km and 40 km TT. Key variables of interest were Watts at thresholds. For VT determination we used: breakpoint of ventilatory equivalent of oxygen (VE/VO2); breakpoint of ventilatory equivalent of carbon dioxide (VE/VCO2); V-slope; respiratory exchange ratio (RER) 5 1 and 0.95. For LT we used Stegmann’s individual anaerobic threshold; the stage preceding the second 0.5 mmol L 1 increase (Baldari); 4 mmol L 1; 1 mmol L 1 increase in 3 min; the stage preceding the first 1 mmol L 1 increase as criterion methods (o1 mmol). Analyses also included peak power during the incremental threshold tests (MaxVTwatts, MaxLTwatts) and 5 km performance (5Kavgwatts). Results: Regression analyses be-
tween VT variables and 40Kavgwatts were significant for V-slope (r2 5 0.63), VE/VO2 (r2 5 0.64), RER0.95 (r2 5 0.53), RER1 (r2 5 0.57), and MaxVTwatts (r2 5 0.65). Regressions between LT variables and 40Kavgwatts were significant for Baldari (r2 5 0.52), 4 mmol L 1 (r2 5 0.36), o1 mmol (r2 5 0.35), Keul (r2 5 0.34), and MaxLTwatts (r2 5 0.51). Regressions between 5K variables and 40Kavgwatts were significant for 5Kavgwatts (r2 5 0.58). Paired t-tests between these variables and the 40Kavgwatts indicated that absolute power outputs at VE/VO2 (P 5 0.33), RER0.95 (P 5 0.93), and 4 mmol L 1 (P 5 0.39) were not significantly different from 40Kavgwatts. Conclusion: We conclude that VT-based variables are generally superior to LT variables relative to predicting 40Kavgwatts, the simplest of several valid measures appears to be VE/VO2.
Although VO2max has traditionally been considered the ‘‘gold standard’’ for evaluation of endurance performance (Costill, 1967; Saltin & Astrand, 1967), recent evidence suggests that a performance threshold (PT) (often imprecisely referred to as ‘‘anaerobic threshold’’) provides a better index of aerobic endurance and therefore may be a better predictor for submaximal endurance performance (Davis, 1985; Londeree, 1997) than VO2max. The term PT is adopted to replace the term ‘‘anaerobic threshold’’ in this study. The PT is commonly determined using either blood lactate (lactate threshold (LT)) or ventilatory gas (ventilatory threshold (VT)) parameters. A wide variety of diagnostic strategies for each threshold have been described in the literature. The assessment of the PT from ventilatory variables (Wasserman & McIlroy, 1964), lactate analyses (Keul et al., 1979), or from a combined analysis of ventilatory and lactate variables (Beaver et al., 1986) has been refined over the years. Nevertheless, controversy continues to persist regarding the relationship between the LT and the VT. Some believe that there is a strong physiological linkage
between VT and LT (Anderson & Rhodes, 1991; Burke et al., 1994) while others believe it is coincidental (Gladden et al., 1985). Regardless, numerous studies have suggested that identifying physiological parameters, such as LT and VT, and associated variables (Watts, HR, VO2, lactate) may be useful predictors of endurance exercise performance. The goal of this study was to identify which of several widely used laboratory-based tests best predicts 40 km cycling time trial (40K) performance. The novel idea was to directly compare and evaluate a variety of different PT identification methods. Methods Subjects Fifteen experienced male road cyclists (Table 1) volunteered for this investigation. Written informed consent was obtained from each participant. The protocol was approved by the institutions’ human subjects committees.
Study protocol For 3 days prior to and during the study, subjects followed a high-carbohydrate diet, and small volume of low-intensity
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Amann et al. Table 1. Anthropometric and training history data (mean SD); N 5 15
Age (years) Body weight (kg) Height (cm) VO2max (mL kg 1 min Years of training Years of racing km year 1 h year 1 USA Cycling Category
1
)
31.5 8.5 70.2 8.2 175.1 5.2 68.6 4.2 9.3 4.4 7.3 3.3 14000 5400 667 182 I–II
training was performed. For the 24 h prior to testing sessions, the subjects were instructed to avoid strenuous physical activity, including high-volume and/or high-intensity training sessions. A practice 40K was performed 1 week prior to the beginning of the study to ensure habituation to the protocol. A series of tests (LT test, VT test and 5 km cycling time trial (5K)), separated by 48 h, was performed by each subject over a 5-day period. The LT and VT tests were performed in random order. The 40K was performed 72 h after the 5K. The 5K was designed to act as a ‘‘peaking’’ workout. All tests were performed on an electrically braked bicycle ergometer (Velotron Electronic Bicycle Ergometer, Elite Model, Racer Mate, Seattle, WA, USA) that was modified with a racing saddle, adjustable stem, and the subject’s pedal system. Velotron is a computer-controlled, electronic bicycle of a proprietary new design (patent pending) with associated interactive Windows PC software. Distance, speed, and workload (considering bodyweight) are calculated electronically. The design uses an electronic (eddy) current to brake a heavy (55 lb), largediameter flywheel with an internal freewheel. Gear shifting is accomplished electronically through the PC control software during the time trial.
2400, Sandy, UT, USA). Peak power output (MaxLTwatts) was computed as follows (Kuipers et al., 1985): Wmax 5 Wf1[(t/ D P)], where Wf was the value of the last completed workload (in Watts), t was the time the last uncompleted workload was maintained (in seconds), D was the duration of each stage (in seconds), and P was the power output difference between workloads.
VT test The VT test began at a power output of 20 W and the workload was increased by 25 W min 1 to exhaustion (Lucia et al., 1998). Such stage durations and workload increments are commonly cited in the VT literature (Beaver et al., 1986; Lucia et al., 1998, 2002). The participants were free to choose any constant pedal cadence between 70 and 120. The test was terminated when the pedal cadence could not be maintained at 70 r.p.m. Heart rate and gas exchange data were collected continuously. VO2max was recorded as the highest VO2 obtained over a 20 s averaging period and the peak power output (MaxVTwatts) was computed using the equation described above.
5 km and 40 km time trials During the 5K, gas exchange data were measured continuously and an arterialized blood sample was collected immediately after exercise. During the 40K, VO2 was measured every 5 km for 2 min, blood samples were collected every 5 km, and the heart rate was recorded continuously. 5K performance variables were time to completion (5Ktime) and mean power output (5Kavgwatts). 40K performance variables were time to completion (40Ktime) and mean power output (40Kavgwatts). In addition, the mean blood lactate concentration during the 40K was calculated.
Warm-up program Two different 30 min warm-up protocols were used in this study. (1) For the VT and LT tests, the subjects performed a 15 min individual (IW: any preferred workload 150 W) immediately followed by a 15 min standardized (SW; at 1.5 W bodyweight in kg) warm-up protocol. (2) For the 5K and the 40K, subjects followed the SW protocol for 10 min, followed by the IW protocol for 15 min. The IW protocol for the time trials included three 1 min sprints (5th, 10th, 15th min) at any preferred power output. The warm-up period for the time trials were concluded with 5 min of SW. Subjects were allowed to cycle at any preferred pedal cadence throughout the warm-up period. There was no resting period between the warm-up protocol and the following test.
LT test The LT test started at a power output of 100 W and workload was increased every 3 min by 50 W until exhaustion (Urhausen et al., 1993) or when pedal cadence dropped below 70 r.p.m. The protocol was adopted based on the minimum stage duration needed for valid lactate data. The participants were free to choose any constant pedal cadence between 70 and 120. Capillary blood samples were taken from the fingertip at the end of each stage and 1, 3, 5, and 10 min after the test, while the subjects cycled at 50 W. Blood samples were analyzed on site using a YSI 1500 Sport Lactate Analyzer (Yellow Springs Inc, Yellow Springs, OH, USA). Heart rate data were measured using radio telemetry (S810, Polar Instruments Inc., Oulu, Finland). Gas exchange data were collected continuously using open circuit spirometry (ParvoMedics, True Max
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LT identification Five common methods were used to identify the LT. The key variables of interest were Watts at thresholds commonly reported in the literature. (1) Determination of the individual anaerobic threshold (IAT) as defined by Stegmann and Kindermann (1982). The IAT is determined according to the changes in lactate concentrations during and after (1, 3, 5, and 10 min post) exercise (Fig. 1). (2) Determination of IAT as defined by Baldari and Guidetti (2000). The IAT corresponds to the power output of the stage antecedent to the second lactate increase of at least 0.5 mmol L 1 above the previous value, where the second increase was greater than (or equal to) the first one (Fig. 2). (3) The power output at a fixed blood lactate concentration of 4 mmol L 1 (Mader et al., 1976) (Fig. 2). (4) Power output at the intersection of a tangent to lactate curve that is parallel to the slope of a 1 mmol L 1 increase in 3 min (Keul et al., 1979) (Fig. 2). (5) The power output that immediately precedes the first 1 mmol L 1 rise that is followed by a similar or larger increase (o1 mmol) (US Olympic Committee protocol) (Fig. 2).
VT identification Five common methods were used to identify the power output at VT. (1) The power output at which the respiratory exchange ratio equalled 1.0 (respiratory exchange ratio (RER) 5 1.0) (Yoshida et al., 1981) and (2) RER 5 0.95 (Wasserman et al., 1994). (3) Ventilatory equivalent method (VE/VO2): the power output corresponding to a systematic increase in the ventilatory equivalent of oxygen (VE/VO2) without a concomitant
Predictors of 40 km time trial performance 9 A
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Fig. 4. Ventilatory threshold identification based on the V-slope method.
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