Cycling for high performance, general fitness or weight loss â€" understand energy needs to get your fueling appropriate.
 
Whether you are new to cycling or a seasoned racing snake, understanding energy expenditure can be valuable for weight management, fueling and refueling. It is little understood with many cyclists still using the kilojoule figure from their heart rate monitor.
 
Energy expenditure and fat loss is a positive side effect of cycling, especially for performance in this power to weight sport. Understanding how energy is used when cycling will help you achieve a leaner physique along with increased performance.
 
Interestingly, that doesn’t mean spending all your rides in the mythical fat burning zone, you need to mix it up with high intensity intervals and aim to use as many calories as you can. A program of training including a small dose of hard intervals mixed in with a large dose of lower intensity riding (70%-80% heart rate) increases your aerobic structure and capacity to use fat for fuel.
 
A little science on energy usage on the bike.
The higher your intensity, the greater your overall energy expenditure (fat and glycogen).  Thanks to power meter technology, energy expenditure can be more accurately measured. 1 Joule of energy equals 1 Watt. If riding at 250Watts, there are 250 Joules of energy/second being delivered to the pedals. As a rough guide though, the human body operates at about 23% efficiency, which means for every Joule you deliver to the bike, you have ‘lost’ a little over 3 Joules metabolising fuels and producing heat. Therefore, at 250Watts, you are actually expending over 1000 Joules (1 kilojoule) of energy/second or 3900kj/hr!
 
To give a better indication of energy cost during cycling, below is a table for a 75kg rider with a 10kg bike riding on a smooth tar surface at various gradients. Of course, riding into a strong head wind versus riding with a tailwind will need considerable more energy.
 

Rider + Bike	Gradient %	Speed	Power	Joules/sec from body based on 23% efficiency	kJ/hr from body based on 23% efficiency	kCal/hr from body
85kgs	0%	25km/h	76	329,84	1187,42	284,07
85kgs	1%	25km/h	134	581,56	2093,62	500,87
85kgs	2%	25km/h	192	833,28	2999,81	717,66
85kgs	5%	25km/h	367	1592,78	5734,01	1371,77
85kgs	6%	25km/h	426	1848,84	6655,82	1592,30
85kgs	10%	25km/h	659	2860,06	10296,22	2463,21

 
 
Does heart rate indicate energy use?
No. Take 2 cyclists pedaling side by side at 250watts, they have the same maximum heart rate, same efficiency and therefore expending the same amount of energy of 1kj/second. However, one is a professional cyclist, the other a recreational cyclist. The pro is riding at a heart rate of 120, the recreational rider at 160 and therefore under considerably more stress. A heart rate monitor showing kilojoules would falsely indicate the recreational rider expending far more energy than the professional because it isn’t actually measuring force, it only measures heart beats and heart beats don’t generate watts, your leg muscles do!
 
Your fitness level governs your capacity to burn fat!
Your aerobic and anaerobic energy systems metabolise fat and glycogen to supply energy for your muscles. As you get fitter, a greater amount of fat will be used as fuel at the same relative intensity, and consequently your cycling speed and endurance will be greater. Your increased aerobic engine comes with an increased capacity to mobilise and transport fat to your muscles, and for the mitochondria in your muscles to oxidise that fat for energy.
 
The bottom line.
Greater fitness from a better-developed aerobic structure allows for increased capacity to oxidise more fat.
The intensity of training dictates total energy expenditure of both fat and glycogen.
Take yourself out of the 55%-65% ‘fat burning zone’ and boost your total energy usage, FAT usage and fitness progress with the following training guide:
 
Take your total weekly hours, e.g. 9hrs.
Spend approximately 80%-90% of your time at 70%-80% heart rate, i.e., 7-8hrs
Spend approximately 10%-20% of your time doing high intensity intervals, i.e. 1-2hrs
 
 

MON	TUE	WED	THUR	FRI	SAT	SUN
Rest	1hr High Intensity Intervals	1hr 70%-80% heart rate	1hr High Intensity Intervals	1hr 70%-80% heart rate	3-4hr 70%-80% heart rate.	2hr 70%-80% heart rate