David J. Bentley

Incremental Exercise Test Design and Analysis Implications for Performance Diagnostics in Endurance Athletes

Physiological variables, such as maximum work rate or maximal oxygen uptake (V̇O2max), together with other submaximal metabolic inflection points (e.g. the lactate threshold [LT], the onset of blood lactate accumulation and the pulmonary ventilation threshold [VT]), are regularly quantified by sports scientists during an incremental exercise test to exhaustion. These variables have been shown to correlate with endurance performance, have been used to prescribe exercise training loads and are useful to monitor adaptation to training. However, an incremental exercise test can be modified in terms of starting and subsequent work rates, increments and duration of each stage. At the same time, the analysis of the blood lactate/ventilatory response to incremental exercise may vary due to the medium of blood analysed and the treatment (or mathematical modelling) of data following the test to model the metabolic inflection points. Modification of the stage duration during an incremental exercise test may influence the submaximal and maximal physiological variables. In particular, the peak power output is reduced in incremental exercise tests that have stages of longer duration. Furthermore, the VT or LT may also occur at higher absolute exercise work rate in incremental tests comprising shorter stages. These effects may influence the relationship of the variables to endurance performance or potentially influence the sensitivity of these results to endurance training. A difference in maximum work rate with modification of incremental exercise test design may change the validity of using these results for predicting performance, and prescribing or monitoring training. Sports scientists and coaches should consider these factors when conducting incremental exercise testing for the purposes of performance diagnostics.

Specific aspects of contemporary triathlon: Implications for physiological analysis and performance

AbstractTriathlon competitions are performed over markedly different distances and under a variety of technical constraints. In ’standard-distance’ triathlons involving 1.5km swim, 40km cycling and 10km running, a World Cup series as well as a World Championship race is available for ’elite’ competitors. In contrast, ’age-group’ triathletes may compete in 5-year age categories at a World Championship level, but not against the elite competitors. The difference between elite and age-group races is that during the cycle stage elite competitors may ’draft’ or cycle in a sheltered position; age-group athletes complete the cycle stage as an individual time trial. Within triathlons there are a number of specific aspects that make the physiological demands different from the individual sports of swimming, cycling and running. The physiological demands of the cycle stage in elite races may also differ compared with the age-group format. This in turn may influence performance during the cycle leg and subsequent running stage.Wetsuit use and drafting during swimming (in both elite and age-group races) result in improved buoyancy and a reduction in frontal resistance, respectively. Both of these factors will result in improved performance and efficiency relative to normal pool-based swimming efforts. Overall cycling performance after swimming in a triathlon is not typically affected. However, it is possible that during the initial stages of the cycle leg the ability of an athlete to generate the high power outputs necessary for tactical position changes may be impeded. Drafting during cycling results in a reduction in frontal resistance and reduced energy cost at a given submaximal intensity. The reduced energy expenditure during the cycle stage results in an improvement in running, so an athlete may exercise at a higher percentage of maximal oxygen uptake. In elite triathlon races, the cycle courses offer specific physiological demands that may result in different fatigue responses when compared with standard time-trial courses. Furthermore, it is possible that different physical and physiological characteristics may make some athletes more suited to races where the cycle course is either flat or has undulating sections. An athlete’s ability to perform running activity after cycling, during a triathlon, may be influenced by the pedalling frequency and also the physiological demands of the cycle stage. The technical features of elite and age-group triathlons together with the physiological demands of longer distance events should be considered in experimental design, training practice and also performance diagnosis of triathletes.

Physiological differences between cycling and running: lessons from triathletes.

The purpose of this review was to provide a synopsis of the literature concerning the physiological differences between cycling and running. By comparing physiological variables such as maximal oxygen consumption (V̇O2max), anaerobic threshold (AT), heart rate, economy or delta efficiency measured in cycling and running in triathletes, runners or cyclists, this review aims to identify the effects of exercise modality on the underlying mechanisms (ventilatory responses, blood flow,muscle oxidative capacity, peripheral innervation and neuromuscular fatigue) of adaptation. The majority of studies indicate that runners achieve a higher V̇O2max on treadmill whereas cyclists can achieve a V̇O2max value in cycle ergometry similar to that in treadmill running. Hence, V̇O2max is specific to the exercise modality. In addition, the muscles adapt specifically to a given exercise task over a period of time, resulting in an improvement in submaximal physiological variables such as the ventilatory threshold, in some cases without a change in V̇O2max. However, this effect is probably larger in cycling than in running. At the same time, skill influencing motor unit recruitment patterns is an important influence on the anaerobic threshold in cycling. Furthermore, it is likely that there is more physiological training transfer from running to cycling than vice versa. In triathletes, there is generally no difference in V̇O2max measured in cycle ergometry and treadmill running. The data concerning the anaerobic threshold in cycling and running in triathletes are conflicting. This is likely to be due to a combination of actual training load and prior training history in each discipline. The mechanisms surrounding the differences in the AT together with V̇O2max in cycling and running are not largely understood but are probably due to the relative adaptation of cardiac output influencing V̇O2max and also the recruitment of muscle mass in combination with the oxidative capacity of this mass influencing the AT. Several other physiological differences between cycling and running are addressed: heart rate is different between the two activities both for maximal and submaximal intensities. The delta efficiency is higher in running. Ventilation is more impaired in cycling than in running. It has also been shown that pedalling cadence affects the metabolic responses during cycling but also during a subsequent running bout. However, the optimal cadence is still debated. Central fatigue and decrease in maximal strength are more important after prolonged exercise in running than in cycling.

Peak power output, the lactate threshold, and time trial performance in cyclists

PURPOSE To determine the relationship between maximum workload (W(peak)), the workload at the onset of blood lactate accumulation (W(OBLA)), the lactate threshold (W(LTlog)) and the D(max) lactate threshold, and the average power output obtained during a 90-min (W(90-min)) and a 20-min (W(20-min)) time trial (TT) in a group of well-trained cyclists. METHODS Nine male cyclists (.VO(2max) 62.7 +/- 0.8 mL.kg(-1).min(-1)) who were competing regularly in triathlon or cycle TT were recruited for the study. Each cyclist performed four tests on an SRM isokinetic cycle ergometer over a 2-wk period. The tests comprised 1) a continuous incremental ramp test for determination of maximal oxygen uptake (.VO(2max) (L.min(-1) and mL.kg(-1).min(-1)); 2) a continuous incremental lactate test to measure W(peak), W(OBLA), W(LTlog), and the D(max) lactate threshold; and 3) a 20-min TT and 4) a 90-min TT, both to determine the average power output (in watts). RESULTS The average power output during the 90-min TT (W(90-min)) was significantly (P < 0.01) correlated with W(peak) (r = 0.91), W(LTlog) (r = 0.91), and the D(max) lactate threshold (r = 0.77, P < 0.05). In contrast, W(20-min) was significantly (P < 0.05) related to .VO(2max) (L.min(-1)) (r = 0.69) and W(LTlog) (r = 0.67). The D(max) lactate threshold was not significantly correlated to W(20-min) (r = 0.45). Furthermore, W(OBLA) was not correlated to W(90-min) (r = 0.54) or W(20-min) (r = 0.23). In addition, .VO(2max) (mL.kg(-1).min(-1)) was not significantly related to W(90-min) (r = 0.11) or W(20-min) (r = 0.47). CONCLUSION The results of this study demonstrate that in subelite cyclists the relationship between maximum power output and the power output at the lactate threshold, obtained during an incremental exercise test, may change depending on the length of the TT that is completed.

Cortical voluntary activation of the human knee extensors can be reliably estimated using transcranial magnetic stimulation

The objective of this study was to determine if a transcranial magnetic stimulation (TMS) method of quantifying the degree to which the motor cortex drives the muscles during voluntary efforts can be reliably applied to the human knee extensors. Although the technique for estimating “cortical” voluntary activation (VA) is valid and reliable for elbow flexors and wrist extensors, evidence that it can be applied to muscles of the lower limb is necessary if twitch interpolation with TMS is to be widely used in research or clinical practice. Eight subjects completed two identical test sessions involving brief isometric knee extensions at forces ranging from rest to maximal voluntary contraction (MVC). Electromyographic (EMG) responses to TMS of the motor cortex and electrical stimulation of the femoral nerve were recorded from the rectus femoris (RF) and biceps femoris (BF) muscles, and knee extension twitch forces evoked by stimulation were measured. The amplitude of TMS‐evoked twitch forces decreased linearly between 25% and 100% MVC (r2 > 0.9), and produced reliable estimations of resting twitch and VA (ICC2,1 > 0.85). The reliability and size of cortical measures of VA were comparable to those derived from motor nerve stimulation when the resting twitches were estimated on the basis of as few as three TMS trials. Thus, TMS measures of VA may provide a reliable and valid tool in studies investigating central fatigue due to exercise and neurological deficits in neural drive in the lower limbs.

Challenging a Dogma of Exercise Physiology

A widely cited recommendation is that to elicit valid maximal oxygen uptake (V̇O2max) values, incremental exercise tests should last between 8 and 12 minutes. However, this recommendation originated from the findings of a single experimental study conducted by Buchfuhrer et al. in 1983. Although this study is an important contribution to scientific knowledge, it should not be viewed as sufficient evidence to support the recommendation for eliciting valid V̇O2max values.At least eight studies have reported that durations as short as 5 minutes and as long as 26 minutes elicit V̇O2max values similar to those derived from tests of 8–12 minutes’ duration. Two studies reported that the shorter test protocols elicited significantly higher V̇O2max V̇O2max values determined during tests of 8–12 minutes than during more prolonged tests, the prolonged tests were associated with maximal treadmill grades of 20–25%, compared with 6–10% in the shorter tests. Therefore, intolerable treadmill grades, rather than the prolonged test duration, may have limited the ability to elicit V̇O2max.In view of the available evidence, test administrators, reviewers and journal editors should not view 8–12 minutes’ duration for incremental exercise tests as obligatory for valid V̇O2max determination. Current evidence suggests that to elicit valid V̇O2max values, cycle ergometer tests should last between 7 and 26 minutes and treadmill tests between 5 and 26 minutes. This is dependent on the qualification that short tests are preceded by an adequate warm-up and that treadmill grades do not exceed 15%. Current research is too limited to indicate appropriate test duration ranges for discontinuous test protocols, or protocols incorporating high treadmill grades.

Specificity of VO2MAX and the ventilatory threshold in free swimming and cycle ergometry: comparison between triathletes and swimmers.

Objectives: To compare maximal heart rate (HRmax), maximal oxygen consumption (V˙o2max), and the ventilatory threshold (VT; %V˙o2max) during cycle ergometry and free swimming between swimmers and triathletes. Methods: Nine swimmers and ten triathletes completed an incremental swimming and cycling test to exhaustion. Whole body metabolic responses were determined in each test. Results: The swimmers exhibited a significantly higher V˙o2max in swimming than in cycling (58.4 (5.6) v 51.3 (5.1) ml/kg/min), whereas the opposite was found in the triathletes (53.0 (6.7) v 68.2 (6.8) ml/kg/min). HRmax was significantly different in the maximal cycling and swimming tests for the triathletes (188.6 (7.5) v 174.8 (9.0) beats/min). In the maximal swimming test, HRmax was significantly higher in the swimmers than in the triathletes (174.8 (9.0) v 184.6 (9.7) beats/min). No significant differences were found for VT measured in swimming and cycling in the triathletes and swimmers. Conclusion: This study confirms that the exercise testing mode affects the V˙o2max value, and that swimmers have very specific training adaptations even compared with triathletes. This may be a function of acute physiological responses combined with the specialist training status of the different athletes influencing maximal cardiac output or oxygen extraction. In contrast, the different training regimens do not seem to influence the VT, as this variable did not differ between the two testing modes in either group.

Throwing Workload and Injury Risk in Elite Cricketers

Objective To investigate the risk between throwing workload and upper limb injury in elite cricketers. Design Prospective cohort study. Setting Elite Australian cricket. Participants 28 adult male cricketers aged 18–32 years. Assessment of risk factors Daily throwing workload and injury were prospectively monitored over the 2007–2008 cricket season. Risk ratios (RRs) were calculated to describe the association between throwing workload and injury. Main outcome measurement Upper limb injury associated with throwing. Results Seven (25%) players sustained an injury during the season. Injured players threw approximately 40 more throws/week (p=0.004) and 12.5 more throws per throwing day (p=0.061) than uninjured players. Players were at a significantly increased risk of injury if they completed more than 75 throws/week (RR=1.73, 95% CI=1.03 to 2.92), and there was a trend towards an increased risk if they completed more than 40 throws per throwing day (RR=1.41, 95% CI=0.88 to 2.26). Injured players also completed more throws and had more throwing days (and consequently less rest days) in the week before injury, as compared with the rest of their season preceding that point. Conclusion An increased throwing workload is a risk factor for the development of upper limb injury in elite cricketers. Investigation of the kinematics of throwing in elite cricketers would complement this study, and further research is required to develop detailed throwing workload guidelines for cricketers across a range of ages.

Physiological responses during submaximal interval swimming training: Effects of interval duration

The aim of the present study was to determine the time sustained near VO2max in two interval training (IT) swimming sessions comprising 4x400 m (IT(4x400)) or 16x100 (IT(16xl00)). Elite swimmers (Mean+/-SD age 18+/-2 yrs; body mass 66.9+/-6.5 kg: swim VO2max 55.7+/-5.8 ml.kg(-1).min(-1)) completed three experimental sessions at a 50-m indoor pool over a one week period. The first test comprised a 5 x 200-m incremental test to exhaustion for determination of the pulmonary ventilation threshold (VT, m.s(-1)), VO2max, the velocity associated with VO2max (VO2max, m(s(-1)) and maximum heart rate (HR(max), b.min(-1)). The remaining two tests involved the IT(4x400) and IT(16xl00) performed in a randomised order. The two IT sessions where completed at a velocity representing 25% of the difference between the VT and the VO2max (delta25%) and in the same work to rest ratio. During the IT sessions VO2 as well as HR were measured. The duration (s) >90% VO2max, also the duration (s) >90% HR(max), were not significantly different in the IT(16x100) and IT(4x400). However, limits of agreement (LIM(AG)) analysis demonstrated considerable individual variation in the time >90% VO2max (mean difference +/-2SD = 222+/-819 s) and the time >90% HRmax (mean difference +/-2SD = 61+/-758 s) between the two IT sessions. This factor deserves further research to establish the characteristics of those athletes which influence the physiological responses in IT of short or longer duration repetitions.

The Relationship Among Peak Power Output, Lactate Threshold, and Short-Distance Cycling Performance: Effects of Incremental Exercise Test Design

The purpose of this study was to compare the physiological results of 2 incremental graded exercise tests (GXTs) and correlate these results with a short-distance laboratory cycle time trial (TT). Eleven men (age 25 ± 5 years, &OV0312;O2max 62 ± 8 ml·kg−1·min−1) randomly underwent 3 laboratory tests performed on a cycle ergometer. The first 2 tests consisted of a GXT consisting of either 3-minute (GXT3-min) or 5-minute (GXT5-min) workload increments. The third test involved 1 laboratory 30-minute TT. The peak power output, lactate threshold, onset of blood lactate accumulation, and maximum displacement threshold (Dmax) determined from each GXT was not significantly different and in agreement when measured from the GXT3-min or GXT5-min. Furthermore, similar correlation coefficients were found among the results of each GXT and average power output in the 30-minute cycling TT. Hence, the results of either GXT can be used to predict performance or for training prescription.