| In both biological and mechanical terms, the bicycle is | | | | running to consume the same amount of energy. |
| extraordinarily efficient. In terms of the amount of | | | | The average "in-shape" man can produce about 3 |
| energy a person must expend to travel a given | | | | watts/kg for more than an hour (e.g., around 200 |
| distance, investigators have calculated it to be the | | | | watts for a 70 kg rider), with top amateurs producing 5 |
| most efficient self-powered means of transportation.1 | | | | watts/kg and elite athletes achieving 6 watts/kg for |
| From a mechanical viewpoint, up to 99% of the | | | | similar lengths of time. Elite track sprinters are able to |
| energy delivered by the rider into the pedals is | | | | attain an instantaneous maximum output of around |
| transmitted to the wheels, although the use of gearing | | | | 2,000 watts, or in excess of 25 watts/kg; elite road |
| mechanisms may reduce this by 10-15% 2 3. In terms | | | | cyclists may produce 1,600 to 1,700 watts as an |
| of the ratio of cargo weight a bicycle can carry to | | | | instantaneous maximum in their burst to the finish line |
| total weight, it is also a most efficient means of cargo | | | | at the end of a five-hour long road race. Even at |
| transportation. | | | | moderate speeds, most cycling energy is spent in |
| A human being travelling on a bicycle at low to | | | | overcoming aerodynamic drag, which increases with |
| medium speeds of around 10-15 mph (16-24 km/h), | | | | the square of speed; therefore, power needs increase |
| using only the energy required to walk, is the most | | | | approximately with the cube of speed. |
| energy-efficient means of transport generally available. | | | | Typical speeds for bicycles are 16 to 32 km/h (10 to |
| Air drag, which increases with the square of speed, | | | | 20 mph). On a fast racing bicycle, a reasonably fit rider |
| requires increasingly higher power outputs relative to | | | | can ride at 50 km/h (30 mph) on flat ground for short |
| speed. A bicycle in which the rider lies in a prone | | | | periods. The highest speed ever officially recorded for |
| position is referred to as a recumbent bicycle or, if | | | | any human-powered vehicle on level ground and with |
| covered in an aerodynamic fairing to achieve very low | | | | calm winds without external aids (such as motor |
| air drag, as a streamliner. | | | | pacing and wind-blocks) is 130.36 km/h (81.00 mph). |
| On firm, flat, ground, a 70 kg man requires about 100 | | | | That record was set in 2002 by Canadian Sam |
| watts to walk at 5 km/h. That same man on a bicycle, | | | | Whittingham with the Varna Diablo II, a highly |
| on the same ground, with the same power output, can | | | | aerodynamic recumbent bicycle. |
| average 25 km/h, so energy expenditure in terms of | | | | There has been major corporate competition to lower |
| kcal/kg/km is roughly one-fifth as much. Generally used | | | | the weight of racing bikes through the use of |
| figures are | | | | advanced materials and components. Additionally, |
| 1.62 kJ/(km•kg) or 0.28 kcal/(mile•lb) for cycling, | | | | advanced wheels are available with low-friction |
| 3.78 kJ/(km•kg) or 0.653 kcal/(mile•lb) for walking | | | | bearings and other features to lower road resistance. |
| running, | | | | In measured tests these components have almost no |
| 16.96 kJ/(km•kg) or 2.93 kcal/(mile•lb) for | | | | effect on cycling performance. For instance, lowering a |
| swimming. | | | | bike's weight by 1 lb, a major effort considering they |
| For many people whose running might be limited by | | | | may weigh less than 15 lb to start with, will have the |
| muscle and knee pain, cycling offers comparable | | | | same effect over a 40 km time trial as removing a |
| outdoor exercise that can be enjoyed by people of a | | | | protrusion into the air the size of a pencil. For this |
| wide range of fitness levels: it is a "no-impact" sport | | | | reason more recent designs have concentrated on |
| that is easy on the body as long as the bike is properly | | | | lowering wind resistance, using aerodynamically |
| "fit." In addition, since bicycling can also provide | | | | shaped tubing, flat spokes on the wheels, and |
| convenient transportation, less self-discipline may be | | | | handlebars that allow the rider to bend over into the |
| required to keep to the activity, since it has a practical | | | | wind. These changes can impact performance |
| purpose. However, because of its efficiency, cycling | | | | dramatically, cutting minutes off a time trial. |
| requires a longer distance, and often greater time, than | | | | |