Power

With the advent of bicycle-based power-meters such as Cycle Ops Power Tap power-measuring hub, or SRMs power-measuring cranks, coaches and athletes are now able to accurately ascertain actual racing/training power outputs. As power output defines our performance, either as power to mass ratio uphill, or power to aero drag in time trials, it is possible to predict actual performance levels, or specific goal improvements needed to meet race/performance criteria. Why should cyclists train with power output, rather than standard measures of HR, RPE, etc.? Heart rate, RPE, and others are not direct indicators of actual cycling performance, i.e., they are dependent upon the actual intensity (power output) of the exercise. It is also well established that there exists a time lag in metabolic responses to changes in power output, such that HR, RPE, blood lactate, etc., do not respond rapidly enough to accurately gauge the intensity of (e.g.) interval work. Furthermore, during training sessions (of both short and long periods) HR can drift, even when the intensity stays constant. This can cause the cyclist to be unsure as to what training zone they are actually in. Because, power-measuring devices can be used as a direct measure in races, race performance can be directly analysed. This enables the coach/sport scientist/cyclist to ascertain exactly at what point they got dropped (e.g., rider was dropped during a sustained hill effort) or why they were able to ride away from others (e.g., TT ability). This then allows specific SMART goals to be set in training so that weaknesses, and/or strengths can be trained. As more and more athletes begin to train with power output, rather than heart rate, or rate of perceived exertion (RPE), guidelines need to be drawn up by experienced users of power output training, such as Sports Scientists, Coaches, etc. Therefore, this article will define a short, reproducible test protocol, and power output training zones. Training and racing zones will be based solely on the result of the test, and can therefore, replace HR training zones. The test is suitable for a wide variety of riders, and the zones have been used with recreational through to professional cyclists. Over the past 6 years Ive developed and refined this eight-zone training system, and a seven-zone race prediction system, based on a short, demanding, test to exhaustion of generally less than 15 minutes duration. The two zone systems are based on the Power Time Curve (Fig 1.) that exists for all athletes. Fig 1

The Protocol

The zones are defined as percentages of maximal aerobic power output (MAP), which is also known as maximal power output, or max-min power output (see Kingcycle Testing). It is the power associated with maximal oxygen uptake (VO_{2 max}) in a continuous, incremental test to exhaustion. It is important to note that there are slight differences between each power measuring system. Accordingly, the rider should not test with one system and train/race with another. It is also imperative, that each power measuring system is correctly calibrated prior to both testing and training, in accordance with the manufacturers instructions. Testing should be conducted on an indoor trainer/ergometer (not rollers) with appropriate power measuring equipment. Riders will need to be well rested, such that they should have a light training week prior to the test. Two days prior to the test, I normally have my riders have a complete day off, whilst the day before, is an easy ride of 45 90 minutes duration. The ramp rate increment, i.e., the rate at, which the intensity increases, is based on gender and broad fitness levels. Starting power output should begin at an easy level, and the test needs to last between ~ 8 15 minutes. Accordingly, for most competitive cyclists over 18 years of either gender, starting power will usually be 100 W or greater.

• Female riders should use a 15 Wmin^-1 ramp rate
• Elite male riders should use a 20 Wmin^-1 ramp rate
• Non-elite male riders should use a 25 Wmin^-1 ramp rate

Rather than have the power ramp up steeply every minute, I split the ramp into small micro units. For instance, with a 25 Wmin^-1 ramp rate, I have riders increase power output 5 W every 12 seconds.

Prior to the Test

The test is similar to a ramped test to exhaustion/VO_{2 max} test/stress test, and although relatively short in duration, does require the rider to push them self to exhaustion it is, therefore, very demanding. Accordingly, prior to testing you should be certain of the following:

• The rider is not currently suffering from any viral, or bacterial infection, or any other illness
• The rider has not had a viral, or bacterial infection, or any other illness within the last four weeks
• The rider does not have any injuries, or recent injuries

The rider should not undertake the test:

• If they are over 35 years of age, or are overweight without first seeking approval off a qualified medical practitioner
• If they are a smoker (or have given up within the last year)
• If they have been diagnosed with any form of heart disease, or suspect heart or vascular disease
• If they are hypertensive
• If they suffer from an airway obstructive disease, such as bronchitis

If you are in any doubt about the suitability of your rider conducting this, or any other physical exertion test then they should consult with a qualified medical practitioner, such as their family doctor, or a doctor who is treating them for any conditions that they may have. The test pushes the body to the limit do not put the rider at risk. Because of the intensity involved, I would also caution against eating within 2 hours of the test, with most people consuming a high carbohydrate meal ~ 3 hours before the test. In the final 2 hours prior to testing the rider should continue to sip on an energy drink.

The Test

Set the riders bike on the trainer, having previously decided on starting power, and ramp rate. Prior to the test proper, the rider should warm up for 10 20 minutes and include a few brief race efforts at the halfway point to get going. Start the test, and set the interval function on the Power Tap/SRM to record the actual test. Ensure that the rider does not exceed the correct power output as the test progresses. Urge the rider to give their utmost as the test starts to conclude this can often produce a few extra watts. Once underway, there are no rest periods as in some tests; the rider should keep upping the power until they can no longer match the predetermined power output. At this point the rider should be encouraged to really dig in giving a final effort to try to match the correct power. During the test, the rider can change gear, and vary their cadence to suit the effort required. I would, however, advise against standing up, as this may cause the trainer/ergometer to topple over. If, during the test the rider appears unduly stressed, then the test should be terminated. As soon as the test is completed, get the rider to switch to a low gear, and make sure that they ride along at an easy level for 10 15 minutes. Ensure that the rider is okay. Stop the interval function on the power-measuring computer. At the completion of the test get the rider to sip on a high glycaemic energy drink, to help restore muscle, and liver glycogen stores. Carbohydrate needs to be consumed at a rate of ~ 1.0 1.5 grams of carbohydrate per kilogram of body mass within 20 60 minutes of the test, to aid glycogen restoration.

Post Test Analysis

Once the rider has recovered, you should download the power-meter, to a PC, where it can then be analysed. Power Tap data will appear as fig 2., whilst SRM data will appear as fig 3. Having set the test as an interval (Power Tap) or markers inserted (SRM) the actual test should be displayed. From, that point the final 60-seconds of the test should be displayed, see, fig 4, and fig 5 for Power Tap and SRM data respectively. It can be clearly seen in both figures 2 and 3 that the ramp rate steadily increases, with a concomitant increase in HR. It is also possible to ascertain HRmax as well during the final 60-seconds, however, with some riders HRmax occurs after the final 60-seconds. Please note: the two tests shown are on different riders, and are thus for illustrative purposes only. Fig 2.
Fig 3 Fig 4. Fig 5

The Zones

Once the final 60-seconds have been displayed, and mean average power calculated termed Maximal Aerobic Power Output (MAP), you can set about defining training zones based on MAP. There are eight zones that I specifically identify six are non-discrete. Sprint training zones are not identified, as they would need to be based on a peak power output test.

Why are some of the zones non-discrete?

Generally, when riding outdoors power fluctuates, due to both environmental and topographical conditions, such as gradient, cornering, traffic, and intensity. Because power can drop rapidly, mean average power can be distorted, and can sometimes not seem representative of what was happening during training. As it is also impossible to exactly hold a specific power output the zones were overlapped to prevent riders worrying about being in the wrong zone. The non-discrete zones also reflect that physiologically, zones are non-discrete and are in continuum. Furthermore, by examining training/race sessions in the power zone histogram function in the Power Tap Link software, or the statistic function in the SRM software you can see what power the rider was at for the majority of the session. Furthermore, modal average power output can easily be identified, thus showing the difference between mean and modal average power outputs. However, when training indoors (e.g., on a trainer, ergometer) mean and modal average power output agree far better as there are few (if any) descents, or corners to coast around! How do the Zones help you? As with any previous training system, such as heart rate, each zone is specifically aimed at various physiological criteria. Zone Recovery: This zone is designed to be a very light workload, such that it causes no significant adaptations, and also limits the cyclist to an easy session, thus preventing a build up of fatigue, or to help in the return after being ill/injured. Zones 1 3: These zones are primarily designed to help with endurance, allowing high volume, low intensity work to be completed. Zone 2 forms the core of an endurance cyclists training programme. At the lower zone, fat is the predominant fuel source, with carbohydrate usage increasing as intensity increases. Zone 4 5: These zones are increasing in intensity, and somewhat-to-very fatiguing. Time trials, and solo/small group breaks in road races are at this level. Lactate levels are just below to above threshold, and carbohydrates are the main energy supply. Zone 6 7: These zones are maximal, and accordingly, rely solely on carbohydrate as the fuel supply. Before attempting training in these zones, the rider must be fully recovered and mentally up for it. At this intensity, the rider is bridging a small gap, or climbing a moderate hill (e.g., up to 5 mins) at maximal effort. Physiologically, youre at VO_{2 max} or above.
Table displaying benefits and characteristics of each training zone:

Can race performance power be estimated?

Although race performance can be down to mental strength, as much as physical ability, a power time curve exists such that the longer the event, the lower the power output. For endurance-based events, an estimate of the power output that can be achieved for a variety of distances is shown below.

Because events such as road races, and criteriums depend on both drafting ability as well as power to mass ratio, it is a little harder to predict power for these events, but, based on experience, the following ranges cover most races, but do bare in mind that these are only guidelines. However, these are not based on % of MAP, but on body scaling. Road races longer than 90 minutes duration are generally between 11 14 Wkg^0.67, whilst short criteriums are generally between, 14 18 Wkg^0.67. Accordingly, for a 70 kg rider, mean average power output would be between 190 241 W for a road race, and between 241 310 W for a criterium.

Take care!

Richard Stern