http://www.shapesense.com/fitness-exercise/muscle-anatomy/ (for above image)
Efficiency is different for everyone. Some people are more efficient with physical activity from being regularly active or even genetics. How efficient you are also relates to the body size. How much energy is used is based on work is being one. For example, a 100 kg rider bikes for half of an hour at a constant speed of 20 km/hr. They will burn a certain amount of energy and from there can determine the power that is being created. A factor that is part of finding the amount of energy expenditure is something known as a MET. A MET is a unit of measurement that determines how much oxygen is needed in 1 kg of body mass per minute (2). 1 MET = 3.5 ml/kg/min which means 3.5 mL of oxygen are used per kilogram of body mass every minute. This number helps find how many Kcals are are consumed every minute. The number MET's for biking at 20km/hr is around 8 (1).
Power produced of a 100kg rider over 30 minute time span
Running at 20 km/hr requires more energy. The number of METs for running at speed of 20km/hr is approximately 12.5 (1).
Therefore, biking will use only 64% of the energy of running at the same speed.
Note: the calculations above are based on theoretical results which may result in partial inaccuracies. This investigation if conducted experimentally would produce different results because of the difference in fatigue to the body between running at biking.
conservation of energy
Biking on uneven surfaces with hills and valleys shows the relationship of kinetic and potential gravitational energy. Assuming that there is no additional forces added to the system and all energy is conserved, then kinetic energy will increase as potential gravitational energy decreases. The same result happens when the potential gravitational energy increases, the kinetic energy decreases. This can be expressed visually of the biker going down a hill and then up an incline. The graph shows the relationship of kinetic and gravitational potential energy:
Calculating the efficiency of above track
Energy transformation diagram
The 14% of the lost energy went to mostly thermal energy and some sound. The efficiency of a bicycle depends on terrain as well. For example, riding over sand will produce a greater rolling coefficient of friction. There is more frictional force involved which explains why there would be significant loss in energy going to thermal. The only way to reduce the amount of energy loss is by moving a smaller load which consists of a rider and bike with less mass. This would produce a smaller normal force, thus a smaller frictional force. The above energy transformation diagram shows that mountain biking begins with chemical energy from the rider. As the rider begins to move, they produce kinetic energy and some thermal energy. When the rider moves and rotates the pedals, the bike begins to move, producing kinetic energy of the bike and thermal energy due to the friction between the tires and the ground.