There are a number of different methods which allow the sport scientist to measure exercise intensity in athletes, however there is a lack of rigidity here and therefore no one ‘gold standard’ method is particularly encouraged for usage. Whilst many of these measurement techniques of exercise intensity are accompanied by advantages, they all of course have their unique methodical design plus practical application flaws and many individual considerations must be taken in to account such as training history and level of fitness. It is highly important that if coaches and scientists alike, are to devise accurate training programmes then the modalities of measuring exercise intensity, must also be extremely precise as it enables a direct prediction upon athletic performance, moreover, reliability and practicality are fundamental elements of the measurement of exercise intensity so that the athlete and coach can utilise the tools on a regular basis easily. In addition to these specifics, measurements of exercise intensity should allow for inter-test reliability and reproductability if they are to be utilised effectively.
In order to best conclude which particular method of exercise intensity measurement is the most favourable, firstly an evaluation of several different approaches to measuring exercise intensity must be established. It has been recognized by many authors that heart rate, VO2 and Blood lactate plus RPE serve as excellent instruments for the measurement of exercise intensity within the sports setting thus these concepts will be explored further.
Amongst other authors Mercer (2001) proposes that measurements of exercise intensity can be problematic; for example measurements of VO2 and the alternative methods such as Max HR percentages do not replicate the metabolic and perceptual strain within individuals of training. Another consideration is that of the nature of the sport itself and whether these different mechanisms for measuring exercise intensity can be used as a “one size fits” all approach to differing sports situations. In order for tests of exercise intensity exhibit versatility they must be applicable to a number of sporting situations; for example in triathlons it is easier for an athlete to use one measure of exercise intensity so that they can focus on their performance, rather than being confused with the data and criterion of many channels at any one instance in time. In addition it is also important to understand the type of physiological demands of the sport itself in order to devise the correct intensity measurement protocol.
Interestingly, Fontana et al (2009) compared different exercise intensity tests when assessing athletes at maximal lactate steady state until time till exhaustion on heart rate, blood lactate plus RPE scales, and measured the versatility of these methods by comparing the differences between cycling and treadmill running. Fontana et al (2009) found that heart rate, oxygen consumption and ventilation were lower for cycling compared to running, whereas blood lactate concentration was higher for cycling. MLSS is similar for cycling and running, despite absolute differences in heart rate, ventilation, blood lactate concentration, and oxygen consumption. This may be explained by the relatively equal cardio respiratory demand at MLSS. This illustrates the fact that inter-test repeatability and the independent strength of these tests are weaker than one would expect since they are commonly sought be athletes and coaches.
Similarly in a study by Zeni et al (1996) which compared the Relationships among heart rate, lactate concentration, and perceived effort for different types of exercise running cycling and cross country ski machine that there were differences with HR across all 3 activities. However blood lactate and RPE measures were consistent with one another on the bike and the treadmill but not the cross country ski machine. Evidently Heart rates will fluctuate according to the activity level therefore we must ask they question- does this mode of intensity testing justify inter-test reliability and repeatability if there are different results for different activities?
It is important to note that because for example the intensity of running slowly and cycling slowly causes a completely different feel for the athlete; that is as the RPM reduces on a bike it can cause increase in tension within the muscle, therefore there are likely to be marked differences within the results of comparative tests of exercise intensity. In fact, Carter et al (2000) found this exact scenario when comparing Oxygen uptake kinetics in running and cycling. The parameters of the VO2 kinetic response were similar between exercise modes, except for the VO2 slow component, which was significantly (P , 0.05) greater for cycling than for running at 50 and 75%D (334 6 183 and 430 6 159 ml/min vs. 205 6 84 and 302 6 154 ml/min,respectively). In a similar test comparing VO2 at similar severe exercise intensities on the cycle ergometer and treadmill Hill et al (2003) concluded that exercise modality does indeed affect the characteristics of the V̇O2 response at equivalent intensities in the severe domain.
On the contrary Caputo & Denadai (2004) compared time to VO2 in runners, cyclists and triathletes along with a control group (eleven untrained subjects) , performed the following tests on different days on a motorized treadmill and on a cycle ergometer: incremental tests in order to determine the VO2max) and the intensity associated with the achievement of VO2max (IVO2max); and (2) constant work-rate running and cycling exercises to exhaustion at IVO2max to determine the ‘‘effective’’ time constant of the VO2 response (sVO2).
VO2 MAX
Maximum oxygen consumption tests are a phenomenon in the sports world. Helgerud (2007) speculates that VO2 max tests are the most fundamental factor in determining success in aerobic endurance, yet individual activities will acquire particular peak o2 uptakes in the same individual. VO2 tests as measurements of exercise intensity are used extensively and aid the indication of endurance capacity in athletes; furthermore they serve as a useful reference when prescribing ideal exercise intensities for individual athletes. It is widely evident that an increase in endurance capacity is partly related to an increased VO2, another reason why this particular method can be utilised as a direct measuring tool for monitoring exercise intensity, however VO2 is not the single indicator of sustaining exercise and therefore relying on the test as the ‘only way’ to measure endurance intensity would be somewhat narrow minded. As early as 1976 Astrand determined the meaning of VO2 MAX, which reflects the physical capacity of an individual to deliver oxygen into the working muscles so that the individual can utilise ATP to meet the working demand. In fact Astrand (1976) also stated that there is a linear increase in o2 uptake with linear increases in work until a maximal work rate has been reached which is illustrated by a plateau in oxygen uptake (l/min). From these initial values one can predict a specific exercise intensity in which an athlete ideally should be working, in order to achieve an optimum training intensity. The advantages of VO2 are that it is highly reliable test for the measurement of aerobic capacity in athletes; its’ strong correlation directly reflects its popular usage amongst endurance athletes. Wells & Norris found that measuring the maximal volume of oxygen relatable to the capacity of the aerobic capacity, Usag & Kandare (2000) reported that a linear relationship exists between oxygen consumption (Vo2) and exercise intensity is a well established phenomenon observed during incremental exercise.
We must remember that despite its high reliability Vo2 max tests to predict exercise intensity are not the ‘be all and end all’. The advances of the criterion it can not be applied within an ordinary training setting easily. Well & Norris agree that in consideration for the equipment-intensive nature of this area of physiological evaluation, it is best suited to clinical and exercise laboratory situations. Perceived exertion scales and HR training have often been used in compliance with this test in order to measure exercise intensity. Brooks et al (2005) correctly points out that if VO2 max were the only predictor of endurance performance then endurance contests would be decided in the laboratory.
PERCIEVED EXERTION SCALES
An example of a very versatile exercise intensity measurement is rate of perceived exertion. The RPE scale is derived from the original BORG scale in 1972 originally was devised to reflect work rates.
Perceived exertion scales are to this day represent a method used for measuring exercise intensity. ‘Psychophysical’ perceived exertion involve the link between subjective and objective work which is illustrated by the usage of a simple scale such as the RPE scale which was initiated by Borg 1962. (Kumar et al 1994). This particular method has been utilised since the early 1950’s to assess the relation between subjective workload and the successive physiological responses to these workloads. The rates of exertion employ the physiological stresses such as heart rate, respiration rate blood lactate and oxygen uptake. The signals that determine the sensation of effort via perception scales such as RPE during muscular exercise have been considered to be of direct relation to peripheral and central origin (Cafarelli 1977, Zeni et al 1996, Crewe et al 2008)) RPE is a physiologically valid tool for prescribing exercise intensity when the intent is to use Lactate as the criterion for intensity (Zeni et al 1996). Paley (1997) confirms that using RPE is a much more practical method than others for measuring exercise intensity for exercise prescription. It becomes apart upon analysing the data, that though RPE can be easily transferred across many different sports, RPE scale cannot be used as an independent measure of tracking exercise intensity.
Wormald et al (2001) found that within their research of cycling trials in different temperatures RPE rose linearly throughout each trial where the exercise temperature condition increased the rectal temperature also increased with RPE (r = 0.92). This study illustrated heart rate increase in RPE predicts the duration of exercise to exhaustion at constant power output during differing environmental conditions. On the flip side Delattre et al (2006) found that Seven cyclists performed an incremental exercise to exhaustion before and after 14 weeks of training using an incremental test to determine their maximal oxygen uptake (VO2max), the velocity associated with VO2max (VVO2max), and the velocity associated with the ventilatory threshold (vVT). Cyclists completed a training record with the actual content and the perceived exertion of each training session during these 14 weeks. The results showed that cyclists were training at a relatively low intensity and that training rating of perceived exhaustion was weak. Moreover, after 14 weeks of training, VO2max did not change whereas VVO2max and vVT increased significantly. Therefore, a discrepancy may exist between what is perceived during training and the effects of training. Consequently, objective and subjective indices collected from training books provided useful information supplementary to that recorded from the physiological indices alone. Suffice to suggest that this method of measurement is excellent as it is truly versatile. Evidence shows that RPE does in fact reflect the central and peripheral intensity signals however one must question this approach because it requires much training for the athlete to fully understand their training intensity in detail. Failing this, the athlete risks misjudging their exercise intensity and thus will not have the ability to enhance their performance, training progressions therefore will be hindered.
HEART RATE
A percentage of maximum heart rate; a commonly used criterion for measuring exercise intensity in athletes, is one method which can help to prescribe steady state exercise to competitor if we are able to map it against another method such as Blood Lactate and VO2. For example, ACSM guidelines currently state that training at 70, 85 and 92.5% HR max can be used as references tools for 60, 80 and 87.5% of VO2 max. Arguably much evidence such as this, illustrates heart rate cannot function as its own tool for the measurement of exercise intensity; instead it must be used in conjunction with other methods in order to maintain accuracy and reliability for athletes. In addition Swart et al (2009) criticise heart rate to be used for the prescription of exercise because it has the potential to be inaccurate if the conditions under which the training is prescribed are not controlled. Maximum heart rate values are often used to formulate percentages of heart rate to prescribe exercise intensity via a widely used equation (220 –age) have for many years been used to measure exercise intensity.. This is where the story gets really interesting because studies have shown significant differences to what athletes have relied on for their training protocol for sometimes their lifetime. An example of this is a study by analysing data from Roekner et al who studied 7397 subjects (age >= 10 yr; 5044 male, 2353 female) found that when testing HR against the measurement of blood lactate at steady state (LASS), using the simple equation of 220 minus age was simply not accurate enough concluding that more information was required than age alone to predict the optimal heart rate for training at LASS.
A meta -analytic approach was used by Tanaka et al (2001) in 514 subjects, they found that heart rate was strongly related to age (r = -0.90), however a different equation was used In the meta-analysis- 208- 0.7 X age. The regression equation obtained in the laboratory-based study (209 - 0.7 X age) was virtually identical to that obtained from the meta-analysis. The regression line was not different between men and women, nor was it influenced by wide variations in habitual physical activity levels. The study on cardiac patients concluded that the current formula (220-age) underestimates maximum heart rate values. If this is the case for cardiac patients then the difference in calculation for the athlete could also be markedly different.
Upon researching there was a myriad of different protocols (Hoogeveen et al 1999, and equations to best predict HR for training for exercise intensity, in conclusion this can be very confusing, it appears that further research is required in this area for reproductability plus a one size fits all approach needs to be established in order for this modality to become more reliable.
BLOOD LACTATE
Blood lactate is another tactic used to measure exercise intensity; however its’ practicality has been questioned in recent research (Zeni et al 1996). The anaerobic threshold, commonly defined as the exercise intensity, speed or fraction of maximal oxygen uptake (VO2max) at a fixed blood lactate level or at a maximal lactate steady-state (MLSS), has been accepted as a measure of the endurance. The blood lactate threshold, expressed as a fraction of the velocity associated with VO2max, depends on the relationship between velocity and oxygen uptake (VO2). The measurement of the post-competition blood lactate in short events (lasting 1 to 2 minutes) has been found to be related to the performance in events (400 to 800m in running). Blood lactate levels can be used to assist with determining training exercise intensity. However, to interpret the training effect on the blood lactate profile, the athlete's nutritional state and exercise protocol have also to be controlled. Moreover, improvement of fractional utilisation of VO2max at the MLSS has to be considered among all discriminating factors of the performance, such as the velocity associated with VO2max (Billiat, 1996). Blood Lactate Threshold is believed to be a more significant ‘anchor point’ for perception of effort (RPE). In terms of the validity of measuring blood lactate response; this particular method of measuring exercise intensity was great for determining elite cyclists from sub elite cyclists during a predicted time to exhaustion test a determinant of Sassi et al (2006) concluded that the type of test utilising blood lactate valid and practical alternative to incremental tests and direct measures of endurance capacity requiring exhaustive efforts for the evaluation of competitive cyclists. Snyder et al (1994) speculated upon there findings suggesting that blood lactate measures can be utilised as key indicators to quantify lactate steady state exercise intensity they were able to devise correct heart rate training zones for cyclists and runners (76 % and 81 % of work bouts were correctly predicted) who were required to use the steady state zone for their training. When examining the practicality of this method to the everyday setting it is viewed as a very complicated method to use for the athlete to use on the field. You must take blood very frequently which can be interruptive of actually training and furthermore because of its high level of invasiveness can actually hinder training intensity. Whilst it serves as an excellent indices tool, in that data can be extrapolated from this method for usage in other simple interventions to measure intensity of exercise blood lactate interventions cannot be relied on as the single most important measuring tool in sport and training except when used in combination with another technique.
CONCLUSION
In conclusion, there is no one method which is robust and versatile enough to rely on for individual measurement of exercise intensity. Each method has their advantages as well as their flaws. The, majority of the time one method relies on another method to increase its validity and usability of measuring exercise intensity. For example, although methods such as blood lactate have been shown to be an extremely reliable intervention for measurement of exercise intensity it is complicated to used in an every day setting although can be used to prescribe more accurate RPE and HR. It seems that the more sophisticated versions of measuring exercise intensity are complex in nature and are difficult to utilise everyday, where as the simplistic versions cannot be used unaccompanied in order to verify them. In the future we should look to find interventions which are more versatile that is whilst maintaining their high level of accuracy being user friendly (accessible, inexpensive practical) is a must for the future, to have a positive effect upon training intensities within athletes.
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