METs are commonly used by clinicians, health educators, and researchers to define, recommend, and prescribe physical activity levels. They can be used to:
- describe an individual’s functional capacity or exercise tolerance
- define a repertoire of physical activities in which a person may participate safely
- compare intensity levels for selected exercise protocols
Here are some examples MET values for different activities:
- Resting or sitting – 1 MET
- Walking at a pace of 4 km/h – 2.9 METs
- Brisk walk at 6 km/hour – 4 METs
- Jogging – 6 METs
- Intensive jump rope workout – 10 METs
How Many Calories Does Bicycling Burn?
In this section, we offer energy calculations for regular bicycles without an electric motor. Bicycling is a form of exercise. While exercising, the three main factors that affect calories burned and ‘weight loss’ are:
- Bodyweight (Wb) – the more you weigh, the more you burn, since more energy is used to move a heavier body.
- Choice of the exercise intensity – more intense activities such as HIIT (High-Intensity-Interval-Training) burn calories faster. Recreational biking, mountain racing, and stationary cycling, each practised for the same duration gives different results.
- Exercise duration – calories burned are proportional to the time duration.
Two techniques could be adopted to calculate the calories burned while bicycling. In the first technique, we can work backwards by initially understanding the power requirements of the bicycle based on its weight, aerodynamic drag, rolling resistance, etc. and then later, account for human inefficiencies to find the calories burned.
In the second technique, we pick up the MET value based on the intensity of the bicycling activity and then directly calculate the calories based on it.
Calorie Calculations Based on Rolling Resistances
The power needed for a bicycle ride is equal to the sum of resistances you need to overcome during cycling, multiplied by your speed. Additionally, power losses in chains and derailleur pulleys are also to be considered. We have based our calculations on the model described in the paper ‘What is slowing me down?’.
The bicycling power equation is as follows:
P = (Fg + Fr + Fa) × v/(1 – loss)…………………….. (6)
where:
P — Power that need to be delivered for the ride;
Fg — Resisting force due to gravity;
Fr — Rolling resistance force;
Fa — Aerodynamic drag;
v — Speed in m/s; and
loss — Percentage loss in power.
Let us look at each resisting component of this cycling power equation in more detail.
Force of Gravity Fg
Fg = g × sin(arctan(slope)) × (M + m) …………… (7)
where: g – Gravitational acceleration = 9.80665 m/s2;
slope – slope of the hill, (positive for going uphill, negative for downhill)
M and m — Weight of the cyclist and the bicycle respectively in kg.
Rolling resistance Fr
Fr = g × cos(arctan(slope)) × (M + m) × Crr,…. (8)
where: Crr — Rolling resistance coefficient.
This represents the friction between your tires and the surface. The smoother the road and the slicker your tires, the less the friction or rolling resistance. The Crr — Rolling resistance coefficient with slick tires for concrete is 0.0020, asphalt is 0.0050, off-road is 0.0200. The Crr with knobby tires with tread/grooves is about twenty percent more: for concrete is 0.0025, asphalt is 0.0063, off-road is 0.0253 respectively.
Aerodynamic drag Fa
Fa = 0.5 × Cd × A × r × (v + w)2 ………………… (9)
where: Cd — Drag coefficient; A — Frontal area; r — Air density; v — speed; and w — Wind speed.
The aerodynamic drag is the force of air resistance and is dependent on your speed raised to the second power – the faster you are, the higher the air resistance. The drag coefficient multiplied by frontal area Cd × A for positions Tops is 0.408, Hoods is 0.324, Drops is 0.307 and Aerobars is 0.2914. Tops position is when the hands hold the top straight portion of the handlebars.
Cycling power losses
Not all of the power that you produce when cycling is transferred directly to the wheels. Some of it is lost either due to the resistance of the chain or the derailleur pulleys. We assume a constant 1.5% loss on the pulleys. The losses on the chain are dependent on its condition:
3% for a new, well-oiled chain;
4% for a dry chain (e.g. when oil has been washed away by rain); and
5% for a dry chain that is so old that it became elongated.
While cycling for leisure, at a speed of 20 km/h, you generate less than 100 W; on a normal training ride averaging 35 km/h, you can reach up to 250 W.
We assume the following conditions for our ride:
Rider’s weight = 65 kgs; Bicycle and gear weight
= 27 kgs; Speed = 21 km/h; Riding position: hoods; Tires: slick; Chain: new and well-oiled; Road surface: Asphalt; Wind Speed = 0 km/h; Gradient = 0 degrees; Elevation = 200 m a.s.l.
The power calculator [3] gives the following output: Power = 67.8 W (or 58.34 kcal/h), and Power-to-weight ratio = 1.04 W/kg.
Considering Human Inefficiency
Humans aren’t efficient engines. While riding a bike, a lot of energy is spent on heat generation, balance and other things. Efficiency of cycling is around 24%. We burn 4 joules of energy for each joule delivered to the pedal or wheels.
From Eq (2) we have:
1 kcal = 4184 J = 4184 W·s
1 J = 1 W·s = (1/4184) kcal …………………………. (10)
Now 1 Wh = 1W × 3600s = 3600J = 3.6 kilojoules…(11)
It is important to highlight that this energy equation refers to the energy available at the wheels or pedals:
1 Wh (at pedals) = (3600/4184) kcal = 0.86042 kcal (at pedals)………………………………………………………… (12)
Since human efficiency is only 24% while cycling
1 Wh (at pedals) = 0.86042 × (100 /24) kcal (of rider’s energy burned)
1 Wh (at pedals) = 3.585 kcal (of rider’s energy burned) …………………………………………………………… (13)
0.2789 Wh (at pedals) = 1 kcal (of rider’s energy burned) Substituting, 1 Wh = 3600 J
3.6 kJ (at pedals) = 3.585 kcal (of rider’s energy burned)
1.004 kJ (at pedals) = 1 kcal (of rider’s energy
burned)……………………………………………………………. (14)
Thus, a very interesting observation is that for every kilocalorie of rider’s energy expended, 1.004 kilojoule, or 0.2789 Wh, of energy gets delivered to the bicycle pedals or wheels.
In our example, if we assume the energy delivered to the wheels is 67.8 Wh, then the rider would have burned 3.585 × 67.8 = 243.07 kcal of metabolic energy.
A gram of body fat stores about 7.7 kcal. Hence, simply divide kilocalories by 7.7 to obtain the weight loss in grams. In our example, weight loss = 243.07/7.7 = 31.56 g.
The calories burned biking calculator gives an estimate of the calories to be burned by the rider to deliver the desired power to the bicycle wheels. By feeding the power at the wheels as 67.8 W, and time of activity as one hour, the calculator arrives at the rider’s calories burned = 243.3 kcal (or 1.018 kJ or 282.77 Wh) and weight loss of 0.0316 kg (or 31.6 g) which are same as the above, hence, verified to be correct.
Calorie Calculations Based on MET Value
The second approach is to estimate the calories burned based on the intensity of the bicycling activity. The MET value for bicycling depends on the intensity of the activity:
- Light effort: 14–15 km/h – 4 METs
- Leisure effort: 16–18 km/h – 6 METs
- Moderate effort: 19–22 km/h – 8 METs
- Racing or vigorous effort: 23–26 km/h – 12 METs
- Mountain biking, uphill, vigorous effort – 14 METs
- Stationary cycling, light effort (90W) – 5.5 METs
The MET for light effort is equal to 4, and the value for somebody taking part in a race and cycling over 32 km/hour can be as high as 16. Since the slabs are coarse and not well defined, we can expect the calories obtained using METs to be a close approximation. Let us assume that riding a bicycle with slick tyres weighing 27 kgs over an asphalt road with no gradient at a steady speed of 21 km/hour represents MET = 4.
Based on Eq. (5), if we wish to find the calories burned by a person weighing Wb = 65 kgs,
Calories burned/hour = METs × Wb = 4 × 65 = 260 kcal/hour
The calories burned biking calculator uses the common formula used by exercise trainers that we have described earlier. In its drop-down menu, if we select the activity as ‘Bicycling at < 16 km/h, leisure to work or for pleasure’,
Calories burned/hour = METs × 3.5 × 60 × Wb/ 200 = 4 × 1.05 × 65 = 273 kcal/hour
In comparison to the value obtained using Eq. 5., here we have a +5% error. We will continue to use Eq. 5 (for better accuracy) as they are derived from oxygen (O2) values rather than the biking calculator that uses a formula with a close approximation.
Energy Calculations for a Solar Assisted Bicycle
Having understood the amount of energy burned while riding a normal bicycle, let us now proceed with the energy calculation in the case of a solar bicycle in a solar assisted pedal mode. For this we need to consider a combination of solar and metabolic energies.
Let us consider a ride in the Solar Assisted Pedal (SAP) mode where the Solar Assist (SAP) Level = ⅖ is selected. In this mode and level, the speed is approx. 21 km/hour. To simplify, let us assume that the destination (place of work) is 11.5 kms away and that the rider spends a total of one hour to and fro, covering a total distance of 21 kms per day.
Let us also assume the same conditions for the ride as earlier, namely: Rider’s weight = 65 kgs; Bicycle and gear weight = 27 kgs; Speed = 21 km/h; Riding position: hoods; Tires: slick; Chain: new and well-oiled; Road surface: Asphalt; Wind Speed = 0 km/h; Gradient
= 0 degrees; Elevation = 200 m a.s.l. For this, the power requirement at the wheels = 67.8 W.
In the solar assisted pedalling (SAP) mode with SAP Level = ⅖ selected, we assume that ⅖th of the total energy, delivered to the wheels, is offered by the solar panel. The balance is offered by the rider as metabolic energy.
Hence, the solar energy delivered at the wheels = 67.8 × ⅖ = 27.12 Wh.
Thus, a solar panel of 40 W which generates a maximum of say 36 Watts on a sunny day (after accounting for conversion losses), would deliver 27 watt-hour of energy to the wheels when the rider is pedalling in the SAP ⅖ mode, and stores the excess energy of about 9 watt-hour in the battery, every hour.
Benefits to a Rider in the SAP Mode
In the SAP ⅖ mode, the balance energy ( 1 – ⅖ = ⅗) delivered at the wheels is the metabolic energy = 67.8 × ⅗ = 40.68 Wh.
Accounting for the human inefficiencies, the calories burned by the rider to deliver the said metabolic energy in the SAP mode = 3.585 × 40.68 = 145.84 kcal.
Compare this with the regular bicycling mode where the entire energy of 67.8 Wh (at the wheels) is expended by the rider by burning 3.585 × 67.8 = 243.07 kcal.
By pedalling in the SAP ⅖ mode, the rider saves 97.23 kcal/hour (approx. 100 kcal/h), representing a benefit of 40% in terms of human calories burnt in comparison to a regular bicycling mode.
The 9 Wh of energy (that we had assumed to be stored in the battery every hour), in actual practice, is observed to be consumed easily and quickly during the ride due to different road conditions such as gradients, asphalt vs. off road terrains, wind gusts and various other obstacles such as pedestrians, traffic signals, speed breakers, etc. This 9W of energy acts as a buffer that smoothes out the ride making it effortless and enjoyable regardless of the terrain.
The potential of the 40 W solar panel to generate solar units far exceeds the consumption needs of a user observing good riding practices! (see section below). We have observed the battery to be usually in the fully charged condition at the end of the day (and also at other times). Solar generation is a continuous process regardless of whether the bicycle is in the (solar assisted) ride mode or waiting for a traffic signal or parked in an open parking lot (under the sun).
Weight Loss
To lose weight you need to have a calorie deficit. A person can choose to work out more or eat less. Working out more is a better option due to the numerous benefits (described above) in addition to weight loss.
If the 145.84 kcal per day burned by the rider in the SAP ⅖ mode is not compensated with extra food intake, then over a month it represents a calorie loss of 4375 kcal or burning of 568g of fat/month. Thus the SAP ⅖ mode, is a very elegant mode to achieve weight loss – approx. ½ kg/month – in a slow and controlled manner.
For the more mentally determined, larger weight loss is also possible, either by pedalling in the SAP ⅕ mode instead of ⅖, or by observing the good practices while riding a solar assisted bicycle. You may also choose a different path or road surface that makes the bike ride more challenging and, hence, more effective in burning calories. You also have the option to switch off solar assist completely, particularly during an up-gradient to convert that short ride stretch into an HIIT exercise for maximising calorie burn rate.
Good practices for a Solar Assisted Bicycle
Maintain the correct speed at each Solar Assist Level
After coming to a halt at a traffic signal, it is a good practice, to shift from Solar Assist (SAP) Level = ⅕ or ⅖ down to SAP Level = 0 by repeatedly pressing the ‘down’ button. When the signal turns green, press hard (manually) on the pedals to accelerate and reach a speed of 14 km/hour. At this stage press the ‘up’ button to shift to SAP Level ⅕.
You now have a choice of maintaining a constant speed of 14 km/hour at SAP Level ⅕ by pressing lightly on the pedals, or to accelerate further by once again pressing hard on the pedals. If you choose the latter, then after accelerating to reach a speed of 21 km/hour, press the ‘up’ button once again to shift to SAP Level ⅖. Maintain a steady speed of 21 km/hour for best performance at Level ⅖.
Refer to Table 2 for the recommended speeds at each of the solar assist levels.
Maintain Correct Tire Pressure
Bicycles tires need to be inflated till they are hard (press between thumb and forefinger to get a feel). Since a bicycle tire is slim in comparison to an automobile tyre, the pressure needed is much higher (typically 40 to 50 psi), while the volume is much less. Less volume means that the tires need to be checked more frequently. It is recommended to check the tire pressure before the first ride of the day on a daily basis. Using a manual hand pump to fill air helps burn calories to warm up before a ride.
Oil the Chain
We have seen earlier that a dry chain increases the losses by over 5%. The losses generate heat, due to which a dry chain gets damaged and elongated if left unattended. It is a good practice to oil the chain once a month, and more frequently if the oil gets washed off due to rains.
Keep the Solar Panel Clean, with correct tilt angle
Solar generation decreases considerably if dust accumulates over it. Dirt and stains can be removed easily by wiping the glass with a wet cloth. To ensure that the sun rays fall perpendicular to the solar panel surface, the tilt angle of the panel can also be adjusted depending on the season (more tilt in the winters).
Keep the Lights ON during the day
Safety comes first. Until such a time that we have separate bicycle lanes in India, it is important to observe adequate safety precautions. Always wear a helmet. Wear bright clothing that is visible. Keep the headlight, tail light ON at all times regardless of whether it is day or night. Ride near the edge of the road – close to the curb so as to give way to the faster moving vehicles. Keep glancing at the rear-view mirror frequently to identify fast moving vehicles, behind you, attempting to overtake you.
Benefits of Riding a Solar Assisted Bicycle
- SMART Goals: Riding to work or school with a solar assisted bicycle is an exercise program with SMART – Specific, Measurable, Attainable, Relevant and Time-limited – goals. One of the goals could be to reduce stress in your life. Another goal could be to reduce your fat. Or it could be to build muscles. Performance improvement could be yet another goal.
- Saves Time: Since going to work or school is a regular activity, you do not need to carve out time or schedule it throughout your week. Clubbing the ride with work – solar assisted bicycling becomes more regular than going to a gym.
- Improves Mood, Body & Mind: Riding a solar bicycle is an aerobic exercise that pumps up the production of your brain’s feel-good neurotransmitters, hormones such as serotonin endorphins, oxytocin, dopamine and molecules such as endocannabinoids.
- Serotonin: When you pedal outdoors under bright light, your body releases more tryptophan, the amino acid your brain uses to make serotonin. The boost in serotonin is why many get the feeling of euphoria known as a ‘runner’s high’ after a ride. It boosts your mood. You feel happy and all seems right with the world. It has been observed that solar bicycle owners step outside and pedal more regularly than other cyclists and generally in a happier mood more often.
- ‘Endorphins’ are the body’s natural painkillers. The name comes from the term ‘endogenous morphine’. “Endogenous” because they’re produced in our bodies; morphine refers to the opioid painkiller whose actions they mimic. Released by the hypothalamus and pituitary gland in response to pain or stress, this group of peptide hormones both relieves pain and creates a general feeling of well-being. Solar assisted bicycling permits exercising at a moderately intense pace that seems best for releasing your body’s endorphins in a desired manner.
- Oxytocin, nicknamed ‘love hormone’, also promotes positive feelings. When you ride a solar bicycle along with your partner it boosts oxytocin naturally and this has a positive impact on your social behaviour related to relaxation, trust and psychological stability. Oxytocin production has a positive feedback loop!
- Dopamine helps us feel pleasure as part of the brain’s reward system. Riding a solar bicycle leisurely can trigger a ‘dopamine rush’. Dopamine is also involved in reinforcement (addiction), you might come back for another one (or two, or three) rides. But unlike drugs that lead to addiction (intense feeling of reward), with a solar bicycle since metabolic energy, that gets exhausted, is involved, this is not the case. Increasing your natural dopamine might help stave off early symptoms of Parkinson’s disease. Safer and more effective than medications like levodopa that have side effects. Besides mood, movement, sleep, dopamine also improves learning and attention that is important for children.
- Clinical Endocannabinoid deficiency causes migraine, fibromyalgia, irritable bowel syndrome conditions – often together and all resistant to treatments. Riding a solar bicycle is the missing key to treatment.
- Stress Buster: It also has direct stress-busting benefits. Stress relief leads to positive effects in your body – including your cardiovascular, digestive and immune systems. It can also minimise your risk of developing heart disease.
- Increased Self-confidence: Regular rides can increase self-confidence, improve your mood, help you relax, and lower symptoms of mild depression and anxiety.
- Improves Sleep: Solar Bicycling can also improve your sleep, which is often disrupted by stress, depression and anxiety. Together, these benefits can ease your stress levels and give you a sense of command over your body and your life.
- No Sprains and Strains: A high intensity (HIIT) exercise is not for everyone and your muscles and joints may pay the price through sprains and strains. Unlike HIIT, solar assisted bicycle rides are gentle on your body and a great alternative to maintain your regular exercise routine. You do not need great motivation, nor physical stamina, to go for a solar assisted ride. You do not need to push yourself to the limit and the solar energy assists you while riding the bicycle.
- Safety Features: Without proper lights, a bicyclist’s life could be in grave danger. Since a solar bicycle is equipped with a headlight, tail-light, brake light, horn and bell, it gets easily noticed even by fast moving vehicles and this helps considerably in reducing the accident rates. Particularly in India, with the absence of separate bicycle lanes or even specially demarcated lanes for bicycles on regular roads, bicycles which are not easily visible or noticeable to the fast moving heavy vehicles could be life-threatening.
- Manage Gradients with Ease: You can confidently ride uphill or on an up gradient such as flyovers, bridges, etc. instead of walking along with your bicycle. You can maintain a steady speed of 21 kms/hour in the solar assisted pedalling mode ⅖ regardless of the gradient, nature of road surface, wind velocity, and such other speed reduction situations.
- Reach Destination on Time: If your workplace is 7 kms away, the ability to maintain a steady speed of 21 kms/hour means that you can more confidently reach your destination in 20 minutes. With no traffic jams on bicycle lanes, one can estimate the time of arrival at the destination more accurately.
- Easy Transition to Throttle Mode: In case there is an immediate need to overtake an obstacle at a higher speed, you can twist the throttle lever to momentarily increase speeds to 25 kms/hour. The bicycle has an ability to seamlessly shift from SAP mode to the throttle mode and back to suit the rider’s needs.
- Easy Transition to Unpowered Mode: Simply press the ‘-’ button repeatedly to lower down the solar assist level till you reach SAP level ‘0’. This will cut off solar and battery feed to the motor regardless of throttle position or pedalling state; while maintaining the headlights and tail lights. The unpowered mode is particularly useful if you are low on battery charge or if you are interested in an HIIT to burn more calories by pedalling without assistance.
- Calorie Calculator: From your solar assisted ride, you can calculate the calories burned and learn about your performance, health, and even the state of your body. Not only are calories a common way for people to measure the level of activity they perform, but it also helps you better plan your nutrition. It provides a measure by which you can set goals, be it fat loss, performance improvement, or building muscle.
To be continued…
Vithal Kamat has a Doctorate in Artificial Intelligence from the University of New Brunswick, Canada as a Commonwealth Scholar in 1996. He completed Masters in Control and Instrumentation from IIT Bombay. He is associated with the Centre for Apparent Energy Research, Anand, Gujarat.
