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ASK PPCC: What is 'gross efficiency' and how do you improve it?

Ever been riding in your local bunch or club race and there’s that one rider who seems to be doing it effortlessly? Maybe you have been left in awe watching a World Tour race through the French alps or Belgian cobbles, where the winner seems to have an infinite amount of watts. 

 

Gross efficiency (GE) is an untapped measure for endurance sport performance, viewing the power output relative to your total energy expenditure for that given moment. Essentially, it shows how much of your expended energy is actually pushing the pedals (1). For road cyclists, GE usually falls between 18-23%. This may seem like a minor metric due to the narrow range of potential improvement of just a few percentage points.


However, let's put this into perspective: an athlete with a GE of 18% could boost their power output by an impressive 28% at the same energy expenditure if they improve their efficiency to 23%. This seemingly small improvement can make a significant difference in performance (2).

 

Whilst this is all nice, exciting and a neat piece of maths, how can we actually achieve this outcome?


Biomechanics - Bike Fit


Whilst cycling is limited in terms of the direction our joints can move, a bike fit can ensure that limited movement is transferring into the pedals. When a cyclist places themselves in a position on their bike that exceeds their range of motion, alternate movement strategies are required to rotate the pedals. Examples of this include rocking at the hips when the saddle is set too high or poor knee tracking when hip flexion range is exceeded.

Studies have investigated crank length and their implications on joint kinematics and GE with results showing that utilising a shorter crank option reduced hip and knee range of motion and had a significant improvement on GE (3).


Utilising both quantitative data such a pedal analysis tool to identify how effective a rider is pedalling whilst using it as an indirect measure of kinematics, coupled with a knowledge base to add in qualitative data provides an optimal platform to get the best fit for you.


 


Muscle Fibre Composition


A very positive correlation lies between Type I muscle fibre percentage and GE, with an athlete with a greater composition of Type I fibres leading to a more efficient athlete (2)(4). These fibres are often referred to as “slow twitch muscle fibres” and have a slower rate of contraction and produce the least amount of force comparison to other muscle fibres, but they have a greater density of mitochondria and capillaries.


Altering muscle fire composition is no easy feat however, with a great importance on a greater training volume, consistency with GE progressively improving over the course of several training and racing blocks(7)(5). In addition to many other benefits, the currently very popular trend of zone 2 training facilitates a great response for recruiting Type I muscle fibres.


Heat Training


So if only around 20% of your energy is converted into watts to move the bike forward where does the rest go?! Well for the most part the rest is converted into heat, we know this all to well when we are riding maximally, our core body temperature rises and we begin to overheat like a car with a broken radiator.


Studies have indicated that riding in temperatures exceeding 30 degrees can have a significant impact in reducing an athletes GE (8) with the likely cause being a shift in energy being required to try and keep the body cool. It would then be logical to suggest that adapting to exercises in the heat and being able to utilise cooling strategies during events in the heat will have a great benefit to sustaining your efficiency during the heat, but I’ll leave this for my partner in crime Jack to talk about in another article.




Training Intensity


Whilst training intensity distribution needs to consider many factors and should be specific to your target goal or periodised appropriately, studies suggest that high intensity training provides a great stimulus to increase efficiency.


Another interesting study looked at training intensity distribution with one group being restricted to low intensity training for 12 weeks whilst the other group having zero intensity restrictions. Interestingly, the latter group showed greater improvement in efficiency in the first 6 weeks with no significant change for the remainder of the 12 week block and the former group requiring the full 12 week block to make a similar improvement to their efficiency. This is likely due to the time required to gain an adaptation to type I muscle fibres as stated earlier, but provides an interesting discussion around needing training intensity to be varied and periodised correctly.



Summing It Up


Whilst there are a lot of moving parts to improving our gross efficiency, focussing on improving this can possibly yield some very large improvements in our performance.


There are a lot of mechanisms involved, with varying training modalities and intensities that need to be periodised effectively. It is worth keeping in mind that this is just one facet of many that improves endurance performance, and training shouldn’t be tunnel visioned into exclusively improving this metric. Training should be tailored towards your own personal endeavours, however gross efficiency may play a role in your performance.


Whilst this is a general overview of this topic there is a lot of emerging science surrounding gross efficiency, and how to improve it. If you would like to know more get in touch!




References


(1) Coyle EF. Integration of the physiological factors determining endurance performance

ability. Exerc Sport Sci Rev. 1995; 23 25-64


(2)Coyle EF, Sidossis LS, Horowitz JF, Beltz JA. Cycling efficiency is related to the percentage oftype I muscle fibers. Med Sci Sports Exerc. 1992; 24 782-788


(3) O’Hara, C.R. et al. (2019) ‘Effects of bicycle crank length on gross efficiency, power, and joint kinematics during cycling ergometry’, Medicine & Science in Sports & Exercise, 51(6S), pp.52–52. doi:10.1249/01.


(4)Hansen, E.A. and Sjøgaard, G. (2006) ‘Relationship between efficiency and pedal rate in cycling: Significance of internal power and muscle fiber type composition’, Scandinavian Journal of Medicine & Science in Sports, 17(4), pp. 408–414.


(5) LUCA, A. et al. (2002) ‘Kinetics of &OV0312;O2 in professional cyclists’, Medicine and Science in Sports and Exercise, 34(2), pp. 320–325.


(6) Hopker J, Coleman D, Passfield L, Wiles J (2010) The effect of training volume and intensity on competitive cyclists’ efficiency. Applied Physiology Nutrition and Metabolism, 35: 17–22.


(7) Hopker J, Coleman D, Passfield L (2009) Changes in cycling efficiency during a competitive season. Medicine and Science in Sports and Exercise, 41: 912–919.


(8) Hettinga, F.J. et al. (2007a) ‘The effect of ambient temperature on Gross-efficiency in cycling’, European Journal of Applied Physiology, 101(4), pp. 465–471.



Author:





Pinnacle Performance Cycling Coaching

Dylan Lindsey

BExSportSc












This article is part of our new casual-science series "ASK PPCC". If you would like to request a topic, or learn more about our covered topics, don't hesitate to get in touch!

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