Power output: Outdoors v Indoors


We have all been there. A training session on the road like any other exacted with strength and clinical precision. Data uploaded, protein drink at the ready as you drool over your numbers with sheer pride in your work. You cruise into the office showing your feathers like the Peacock of Power. Life is good.

The following week, you repeat the same session indoors, and it is an apparent disaster. You're not even within touching distance of the

numbers you produced outdoors.

Questions begin to run around your head:

Is my form gone? Is my training wrong? Am I getting sick? You’ll be glad to know however, it is most likely none of these. Instead it is a result of a combination of factors which include the environmental conditions around you, physics, and your psychological perception.

The Body and Efficiency

Primarily, it rests with how efficient we are, and how that is impacted when we compare the two scenarios in question. Of the energy we consume when riding a bike, roughly 22% of that goes into putting power through the pedals. The remainder is lost to other bodily processes such as temperature regulation (sweating and shivering), digestion, respiration and excretion among others.

Never mind the Biology lesson

Heat is one of the primary culprits of such a drop in efficiency. In a study conducted by the International Journal of Sports Physiology and Performance in 2011, nine highly trained cyclists completed four 40km time trials in an environmental chamber at 17, 22, 27 and 32 degrees respectively. The findings were not unsurprising, but stark nonetheless. On average, power had dropped 20w between the 17C and 32C effort. The temperature was the only variable here, and it accounted for, on average, a 6% drop in power output.

It therefore goes without saying that addressing this issue if you have not already done so, will go a long way in bridging much of the gap between your output on the road and the turbo trainer. A bigger and better fan and training in the garage or on the porch rather than the living room are two easy solutions.

Remember: The puddle of sweat below you should not represent how hard you worked, but instead how much harder you could have worked. (And don’t forget the same rules apply to regular riding – over or under dressing on training rides will have the same effect)

Inertia “Inertia is the resistance of any physical object to change in its state of motion”. Put simply, when riding a bike outdoors, we have the inertial load of ourselves and a bike moving forward at a given speed, but on the turbo trainer, we do not. Instead, it is only the rear wheel and/or a weighted flywheel. The mass of this is less significant when contrasted with the total weight of ourselves and a bike: 5-15kgs vs. 70+ kgs.

This is what brings about the all too common feeling similar to that of riding through mud, when on an indoor trainer. The reduction in inertial load exaggerates the dead spot in the pedal stroke and as a result power output will fall.

The best solution to this issue is choosing the best weight and size of the flywheel when purchasing your next indoor trainer. New direct-drive turbo trainers have come a long way in developing a road-like ‘feel’, with flywheels of up to 15kgs making a big difference in power output indoors and go some way to bridging the gap. Mentality We all know it can be mentally tough taking on an indoor session. Boredom, increased perceived effort, temperature control and missing the road. Having a clearly outlined objective for the indoor sessions, adding comfort with a good fan and using music will go a long go a long way towards your experience being a pleasurable one.

Embrace the technology Software such as Zwift, TrainerRoad and Garmin IQ are excellent additions in terms of user stimulation and also give you the ability to upload your own workouts to them. Anything that can maintain the quality of your training and even enhance it with the mental stimulation the virtual environment provides must be a good thing.

Embrace the technology and use your coaching and planning effectively to get everything possible from your effort regardless of the weather.

Should I alter my training zones? We are often asked whether having two sets of training zones is a good idea if you struggle with a much-reduced power output indoors. Generally, it is advised against, as it would require testing too often if you were to carry out an FTP test on the road and indoor trainer every four weeks.

Instead, aim to set your training zones based on where you will do the majority of your training. Be realistic when you set out to do a session indoors, if you are using zones set from data collected outdoors. A good coach regularly connecting with his athlete will alter to the needs of the conditions regularly.

If you find for example that you are generally 20w down when riding indoors, do not belligerently set out to hit the numbers you would on the road, and subsequently fail to complete the training session set. Instead look to revise the targets for respective efforts downward by 5-10% when riding indoors. If you are using Zwift with a customised .ZWO file as Elevation Coaching provides you can make use of the FTP bias button to adjust your workout up to +/- 10% on the fly, allowing a one click adjustment to move from outdoors to indoors. A note of caution using heart rate should be taken. Heart rate is impacted by variables directly impacted by indoor conditions, heat being a primary example. In this case, use your perceived rate of exertion as well as heart rate. Conclusion

Ensure that the training sessions that you do indoors are best suited to that scenario. For example, sprint sessions or long endurance rides, are less suited as you may not be able to attain the peak power outputs or duration required for these sessions.

Instead, plan in advance, be flexible with your training, and communicate with your coach to adapt to the indoors to ensure you are training to the maximum.

Key Points

  • Heat dramatically hinders performance

  • Less inertia exaggerates the dead spot

  • Mental preparation combined with training aids will enhance the experience

  • Adapt your goals and alter your training zones with the help of your coach to get the most from the indoors

References: Peiffer, J., & Abbiss, C. (2011). Influence of Environmental Temperature on 40 km Cycling Time-Trial Performance. International Journal of Sports Physiology and Performance, 6(2), 208-220. http://ro.ecu.edu.au/cgi/viewcontent.cgi?article=1179&context=ecuworks2011


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