Physiological Assessment in Cycling
We’ve already seen that elite cyclists can’t afford to guess at their form – they need hard and fast numbers from tests to work out how hard to train, or whether to rest. But how are these tests carried out and how can the results help physiologists and coaches to plan better training programmes? Greg Whyte explains
The sport science support team represents a multi-disciplinary group of subject-specific experts from a wide range of disciplines whose role is to work in an interdisciplinary fashion with other science (and medicine) specialties to enhance cycling performance. The core support team include specialists from the fields of biomechanics, physiology, psychology, nutrition, performance analysis and strength and conditioning. This team interacts directly at the coach-athlete interface to offer expert solutions and knowledge, leading to an enhancement of training and competition performance.
The role of the physiologist as part of the interdisciplinary team is to provide expert solutions and knowledge to a wide range of issues related to training and competition performance, as well as cyclist health (1). One of the key areas of intervention is the identification of the physiological determinants of performance and the assessment of those determinants.
While coaches and cyclists are able to identify overall variations in performance, the physiologist is able to dissect overall performance into its component parts through physiological assessment, allowing a more detailed interrogation of performance.
Physiological assessment is used as an intimate part of the ‘training triad’ consisting of three elements:
1. Profiling – profiling various determinants of performance allows comparison with ‘gold standard’ values;
2. Prescription – prescription of training through identification of strengths and weaknesses from profiling and identification of training intensity zones, often using heart rate or power output, can optimise the training stimulus;
3. Monitoring – monitoring subsequent training adaptations allows continuous evaluation and optimisation of the training stimulus.
Recent debate regarding physiological assessment has focused on the role of laboratory- versus field-based testing. The limitations of laboratory-based testing and the benefits of field-based testing can be largely encapsulated in the concept of specificity – ie it can be very difficult, when using laboratory- based ergometers, to replicate the exact movement patterns and limb velocities that actually occur when cycling on the road or to utilise exactly the same muscle groups.
However, laboratory-based testing also has its advantages. While field-based testing provides information and data that is more ecologically valid, the downside is that it may lack control and therefore often lacks reliability. Unlike laboratory-based testing, field-based testing is subject far more to the vagaries of the weather and to the idiosyncrasies of location and topography and the presence or absence of others. Laboratory-based testing might reduce ecological validity, but it enhances reliability and allows measurements to be taken that would otherwise be impossible in field settings.
In an appropriately equipped exercise physiology laboratory, temperature and airflow can be standardised, and the flow of people controlled to limit the Hawthorne effect (Audience effect). These controls improve confidence in the interpretation of results, reflecting changes in physiology rather than the environment. The optimum physiological assessment programme will, of course, utilise laboratory- and field-based testing (2).
Physiological assessment of a cyclist must take place on a bike or cycle ergometer that very closely replicates that cyclist’s individual cycling position, and any assessments must target the principal energy systems associated with his or her performance – eg to properly test the performance of a sprint cyclist would require tests that target the same type of energy systems (anaerobic) used in sprinting (3,4).
Cycling represents a wide range of disciplines that require the full spectrum of energy systems from track sprint through to multi-day tour events. It is beyond the scope of this article to examine the physiological assessment of all cycling events, therefore we’ll examine appropriate testing for single episode endurance races, ranging from the 10-mile time trial through to single-stage racing (circa six hours).
Key determinants of endurance cycling performance
Understanding the key determinants of endurance cycling performance is fundamental to the physiological assessment of a cyclist (5). The key determinants of endurance cycling performance include the following (6):
– Maximum oxygen consumption – usually abbreviated as VO2max
– Oxygen economy – oxygen consumption at a given power output
– Lactate threshold
– Fractional utilisation – oxygen consumption at lactate threshold
– Maximal lactate steady state – (often termed critical velocity
– Peak power output – (power at VO2max).
Any testing programme used to assess an endurance cyclist needs to reliably measure these determinants.
Measuring each of these physiological factors one by one is impractical, both in terms of time and cost, so tests have been devised that assess a number of them simultaneously:
This test consists of six four-minute stages with each stage performed at 20 watts higher power output than the previous stage. An ear lobe blood sample for subsequent lactate analysis is collected in the final 30s of each stage. Heart rates (using commercially available telemetry systems) and oxygen consumption (using indirect calorimetry) are measured throughout the test.
Establishing the target power for each stage begins with the conversion of a recent best time for a 25-mile time trial to an average power. For example, a cyclist with a best time of 60 minutes for a 25-mile time trial would be set 240 watts as the reference power. The fourth stage is then allocated the 240-watt level and the velocities for stages 1, 2, 3, 5 and 6 are calculated by subtracting or adding 20 watts – ie stage 1 at 180W, stage 2 at 200W, stage 3 at 220W, stage 4 at 240W, stage 5 at 260W and stage 6 at 280W. Following the completion of stage 6, power output is increased by 20W every minute until the cyclist can no longer continue (volitional exhaustion).
Derivation of VO2max and fractional utilisation
VO2max is established from a test lasting between nine and 16 minutes. The type of test described above will take around 25 minutes and hence in this instance maximal oxygen uptake is referred to as ‘VO2peak’. VO2peak has been demonstrated to be within 3% of VO2max. Fractional utilisation is the volume of oxygen consumed at lactate threshold expressed as a percentage of VO2max. It is also sometimes used, however, to describe VO2 as a percentage of VO2max (or VO2peak) at a specified intensity – eg the percentage of VO2max being used at 25-mile time trial pace, or at 280W power output.
Derivation of oxygen economy
Oxygen economy refers to the volume of oxygen taken up by active muscles at a given sub-maximal exercise intensity. During cycling on the ergometer, a standard power output may be used for comparison. Reduced volume of oxygen consumed at this sub-maximal power output is interpreted as an improved oxygen economy and improved efficiency and performance. When it’s not possible to measure oxygen consumption, physiologists can also use heart rate or blood lactate concentration at a given power output to derive an indication of efficiency.
However, giving a single target heart rate value to a cyclist wouldn’t really provide useful training information because he or she would need a range of training intensities to properly target the physiological mechanisms underpinning performance. Instead, giving a heart rate range based on the test information is far more practical.
For training outdoors, we would advise the cyclist to use a 10-beat range – ie 135-145 beats per minute. For training on the rollers or cycle ergometer (where weather and terrain do not change), a 5-beat range of 137-142 beats per minute would be given.
Knowing the heart rate at LT allows the heart rates for other training zones to be calculated. For example, base endurance training (long slow distance, LSD) is calculated at 120-130 beats per minute (ie staying five beats below the LT range). Care is needed when estimating maximum heart rate using the common ‘220 – age’ formula, as this method rarely reflects the cyclist’s true maximum heart rate and can lead to inappropriate training prescription.
However, an incremental test also provides a measured maximal heart rate – very valuable for prescribing precise training intensities. The prescription of training using individual heart rate zones allows specific, targeted training prescription that can have a profoundly beneficial effect on training adaptation.
Following a number of weeks of training, retesting our mythical cyclist would reveal changes in VO2peak, fractional utilisation, oxygen economy and lactate threshold. Improved endurance is characterised by a rightward shift in the work rate-blood lactate/heart rate curve.
If training goes particularly well and the prescribed heart-rate zone proves to be ideal for the cyclist, it may also be possible to simultaneously observe an increase in the intensity at which LT occurs.
The RAMP test represents a gradual and continual increase in workload to maximal volitional exhaustion. RAMP tests are commonly used to establish three main physiological markers: VO2max, maximum heart rate and maximum minute power (MMP). MMP is defined as the average power output sustained for the final minute of exercise, and is closely correlated with shorter time trial performances. Using breath-by-breath gas analysis throughout the test, it is possible to identify anaerobic threshold, a point closely reflecting LT, which can be used to prescribe exercise as detailed above (7).
Field-based testing (ie on the road) is more sports-specific than laboratory-based testing. However, because it is very difficult to standardise the test environment from one occasion to the next, it can lack reliability. In short, it tends to be less objective and far more subjective. The tests outlined above can be adapted for use in a field setting with some degree of success, but the best field-based method of physiological assessment is the time trial. Time trialling over a variety of distances can offer a great deal of useful information regarding the full range of energy systems and technical requirements of an endurance cyclist’s performance (8).
Identifying and testing the determinants of performance is fundamental to the physiological assessment of cyclists. The bad news is that these assessments often require significant expertise and experience, and expensive equipment and facilities. The good news, however, is that a number of these tests can be replicated without fully equipped laboratories, for example RAMP testing and time trialling, from which important information, specific to an individual cyclist, can be gleaned and used in the profiling, prescription and monitoring triad. Ideally, a combination of laboratory- and field-based testing should be employed in the physiological assessment of the endurance cyclist.
1. Whyte G (ed) The Physiology of Training, Elsevier Ltd, Edinburgh, 2006
2. CJ Gore (ed) Australian Sports Commission Physiological Tests for Elite Athletes, Human Kinetics, 2000
3. Jeukendrup A and Martin J, ‘Improving cycling performance, how should we spend our time and money’, Sports Medicine 2001; 31:559-569
4. Paton C and Hopkins W, Tests of cycling performance, Sports Medicine 2001; 31:489-496
5. Gore CJ (ed) Physiological Tests for Elite Athletes, Australian Sports Commission, Human Kinetics, Champaign, IL, 2000
6. Shave R and Franco A, The Physiology of Endurance Training in The Physiology of Training (Whyte G ed), Elsevier, Edinburgh, 2006
7. Wasserman K, Hansen JE, Sue DY, Whipp BJ, Principles of Exercise Testing and Interpretation, Philadelphia: Lea and Febiger, 1987
8. BASES Physiological Testing Guidelines, Bird S and Davison R (eds), 3rd edition 1997