Interval Training With Power

Once upon a time, in the post war years, road cycling was as much a pastime as a sport. Large groups of men would get together on Sunday for a so called "club run", a half or even whole day endeavour, probably a great opportunity for a picnic and, dare we escape the wife. As time went on people became richer and the world became more interesting cycling club memberships dwindled but for a committed few, the typical reader of this website who is predisposed to racing, the club run never went away, it just got faster. It is perhaps though an unwelcome artefact of the traditional club run that there are still large numbers of riders, mostly of the older school, who believe that "long, slow, distance training" or LSD is the root of all fitness. We say unwelcome because there is little evidence to suggest that this is indeed essential.

When in 2009 Chris Carmichael released his book The Time Crunched Cyclist (and later The Time Crunched Triathlete) as training regimen for busy riders it wasnt so much a revolution as a formalisation of what we had all been thinking..."I dont have 20 hours a week, I dont need the endurance to race stage races or the spring classics, I just want to be fast enough for a 1 hour race or a sprint triathlon on 6 hours a week". Of course nowadays the "time crunched" cyclist is the norm rather than the exception and coaches are measured more on their ability to deliver training programmes that are both effective and time efficient rather than gruesome and time consuming.

Why Intervals?

When you reduce the volume to create a time efficient training programme you have to increase the concentration of intensity to maintain an adequate training stimulus. You have to compress moments of high intensity riding that would be very manageable physiologically and psycologically if interspersed with hours of lower intensity riding into a tighter, more demanding schedule. More often that not this means interval training sessions because intervals offer a well defined and achievable way to package high intensity training into sessions of minimal length.

Intervals should be embraced because they work but also because they offer great race simulation and, for the rider who trains with power, they offer an opportunity to "chase numbers" which we regard as a positive motivational tactic rather than a practise to be avoided. But the number of different interval workouts that can be identified or proposed is massive. Possible sources of variation are:
  • Intensity
  • Interval length
  • Lengh of recovery periods
  • Number of repetitions
Not to mention the frequency with which the session is to be repeated or the way in which these sessions may be linked and packaged into blocks. Coaches will normally use these sources of variation to:
  • Add variety
  • Simulate race demands
  • Bring on form
  • Try to get athletes over a plateau
  • To create a plethora of complexity that keeps their client on the books. (Beware - Not all coaches are good ones!)

Categorisation of Intervals

To help navigate the potentially complex landscape of interval training we present a categorisation. In terms of each category we explain how the sessions may be designed, we look at their objectives - why you would want to do them, how they work - in terms of the energy system(s) targeted, and where it may not be clear we hypothesise how repeated execution may affect a riders power output.

1) Threshold

Threshold intervals are all about taking the highest intensity we can ride at for an hour, more-or-less equivalent to our 25 mile (40 km) time trial pace, and packaging it into more manageable, repeatable chunks that are less daunting to ride on a regular basis.

A very popular threshold focussed session is the "2x20" or two, twenty minute intervals at the said power output, packaged into a 1 hour session with 10 or more minutes warmup and 10 minutes "easy" in between. Variations on the 2x20 include the 1x20 (equivalent to practising a fast 10 mile time trial) and for more highly trained athletes a 3x20 or 4x20. Arrangements such as 4x15 or 2x30 can work also.

The aim of threshold intervals is to work at or around anaerobic threshold, improving our tolerance to riding at this intensity and ultimately increasing the level of this threshold which can be thought of in terms of a sustainable percentage of HRmax and, accordingly, a sustainable percentage of VO2max. More about that now...

2) VO2max

Recall that a riders VO2max is is the maximum rate at which he can use oxygen to convert food energy into other forms of energy within the body. The actual power he can sustain depends on his threshold (what percentage of VO2max can he sustain) and his efficiency (what percentage of the energy yield from oxygen makes it to the pedals as physical energy, Joules or Wattage (Joules/Time). Accordingly wattage is always some function of VO2max and a higher VO2max should always lead to a higher sustainable power output, even if threshold (%HRmax) and efficiency (%) remain exactly the same. We illustrate this relationship at some length in the our HR-VO2-Power Relationship Model

VO2max intervals are hard efforts of typically 3-5 minutes duration which are ridden at intensities above anaerobic threshold, around 10-25% above threshold power or FTP. The aim of a VO2max interval is to ride at an intensity that will raise the riders rate of oxygen consumption upto VO2max as quickly as possible, perhaps within 1-2 minutes, and then to hold this intensity for a further couple of minutes, thus logging a little more time at VO2max with each interval. In a typical session of 5x4minute intervals with 4 minutes recovery between each a rider might achieve and therefore benefit from training at VO2max for 10 minutes. It is normal to achieve VO2max a little more quickly after the first 1 or 2 intervals (So called "O2 dynamics" dictate this) and a tactic to try and spend more time at VO2max is to reduce the length of recoveries.

Before becoming too ambitious with VO2max intervals, think about the following: The best indication of having reached VO2max is a heart rate at or just below maximum. VO2max intervals will typically finish with the riders Heart Rate at100% of maximum. An so they hurt...a lot! Not all riders have the phsycological strength to execute real VO2max intervals but those that do often achieve rapid enhancements in form.

A variation on VO2max intervals is the Tabata high intensity interval protocol. Ths is a series of 7-8 repetions of 20 seconds ridden at close to 2x FTP with just 10 second recoveries. If anything this is a harder session to complete but the "bang for buck" in terms of physiological returns for time invested can be impressive.

3) Anaerobic

A rider who delivers more power than his threshold output or FTP for any non-trivial amount of time, such as in the last mile of a race or covering a break, is relying on anaerobic energy systems to create more power than is available aerobically. The size of a riders anaerobic engine is known as his anaerobic work capacity (AWC) which can be tested with a power meter and measured in terms of joules. Recall that 1 joule = 1 watt for 1 second and so a certain AWC in joules can be spent as power over any duration. As an example 12,000 joules delivered as 200 joules per second for 1 minute would give a rider 1 minute of riding at 200 watts above his threshold power, alternatively he might spend the same AWC at 400 joules a second giving him 30 seconds at 400 watts above threshold power.

The main aim of anaerobic interval designs is simply to increase anaerobic work capacity via repetitions of intervals in the 30 seconds - 2 minute duration. These intervals can be taxing, and it can take a long time to absorb and build up the benefits, so most coaches program them in a sparse manner. Typical strategies include matching the interval length with the kinds of efforts the rider envisages executing in a race situation, or else simply tailoring the interval length to a local hill, the rider aiming to spend and therefore stretch his full AWC by the top of the hill.

4) Neuromuscular

This is a category of intervals designed to improve a riders ability to deliver power at levels significantly above those that can be met by the anaerobic energy systmem, typically applicable to sprint-like durations, or else to demand particularly high pedal forces with the aim of stimulating neuromuscular adaptations. We could split this category into 3 types:


Most riders are very clear what a sprint is... aproximately 5-10 seconds of all out power. Sprint intervals can be casually inserted a few at a time into longer and lower intensity training rides, or they can be bundled into specific sessions that may include as many as 10-20 sprints with generous recovery. Sprint intervals may be done in big gears (the big ring) to work on muscle force, or else in lower gears (the small ring) to work on leg speed. In both cases the interval ends at exhaustion of the apropriate power output, or on achieving a flat-out leg speed well above typical riding RPM. Sprint intervals may be deliberately executed uphill, downhill, with or into wind.


There are several ways a sprinter can achieve advantage over his rivals: a stronger kick (or jump), faster peak speed, or superior maintenance of a high speed. One only has to reflect on the hype around Mark Cavendish's sprinting dominance to understand the importance of the kick or jump, context-specific words for acceleration. But the ability to accelerate violently is not only important to sprinters, criterium riders may value the ability to acellerate hard out of corners and attacking riders are always looking for more brutal ways to launch a breakaway.

We have seen a couple of different interval workouts designed specifically to improve acceleration in big gears, one emphasising in-saddle accelerations, the other out-of-saddle accelerations. The emphasis here is on improvisation to match event demands.

Big Gears

Some coaches beleive that periods of riding in big gears at low cadence stimulate muscular adaptations, a technique otherwise known as "on the bike resistance training". There is little evidence to suggest that such high force pedalling is required in forms of racing other than track sprinting and we would question the merits of such routines on this basis.

5) Event Simulation

Post race analysis of power meter files can be an extremely valuable source of training ideas because studying the important moments of a race tends to reveal, via identifiable patterns, why some cyclists have the capability to win and why others do not. Equally just thinking about how a race might play out ahead of time, or else studying the demands of the course profile, can be rich sources of ideas for race specific, event simulated interval training sessions.

For Road Racing

A common pattern of power delivery required to win a race is the breakaway. A successful breakaway is initiated with a high burst of power, perhaps 30 seconds of effort at 2 x FTP required to ride clear of a field and then some minutes maintaining a high but maintainable pace, often right on or just above the riders threshold power. Aspiring race winners could do worse than to practise this sort of routine, repetitively, in the style of an interval session.

For Time Trialling

Only a pan-flat, windless course would allow a time-triallist or triathlete to acellerate upto threshold power exactly and then hold that number perfectly until the finish line. The reality is that a well paced time trial see's the riders effort oscillating over and under threshold power depending on the terrain and wind related demands of the course. Reflecting this pattern of power demand is the concept of the "over and under" interval session. Simply put, the rider may elect to complete a certain duration of effort, eg 20 minutes, "around threshold" and then alternate 3 or 5 minute segments at intensities over and under threshold, perhaps 5% of FTP or 10 watts. We feel that the logic behind this session design, which is a clear enabler of intelligent pacing strategies, is so compelling as to be an essential inclusion in the training of time triallists and triathletes.

Micro-Analysis of Race Demands

The technique of "Quadrant Analysis" allows a rider or coach to transform ride data (in particular matched power and cadence data) into a distribution of "Average Effective Pedal Force" and "Circumferential Pedal Velocity" such that clear sectors of power generation can be identified encompassing high versus low force, high versus low pedal velocity, and the 4 combinations thereof. The aim of this type of analysis is to reveal the muscular demands of an event at a very low level, and then to use such analysis to better match (interval) training sessions to race demands. This is a thought-provoking area of analysis and the interested reader may wish to google "quadrant analysis".

Tips for Interval Training

We close this article with 5 common suggestions relevant to best execution of interval training sessions:
  1. A rider should only do intervals when motivated. Just going through the motions at insufficient power outputs is more likely to cause fatigue than improvement.
  2. As soon as a rider fails to hit the target interval insensity, assuming that is well specified, he should abort the session.
  3. Choose the ride environment wisely. Threshold or VO2max intervals may be more easily or more effectively executed on a steady hill. Alternatively threshold and VO2max efforts may be best done under the smooth, controlled resistance of a turbo trainer. Conversely anerobic and sprint intervals are normally better done outdoors because most turbo trainers fail to simulate well the sensation of on-road acceleration and becasue bike control is a complimentary skill.
  4. The very hardest intervals should be done close to home, minimising any tendency to conserve energy for what could be an unpleasant ride home.
  5. Ideally an interval training session occurs on a day when the rider is fresh, often following a recovery day. If intervals must be chained into blocks of consecutive days training work downwards in intensity, eg on day 1 schedule a VO2max interval session, on day 2 a threshold interval session, and on day 3 a lower intensity road ride.