Robert Förstemann is a world, European and multiple German champion in track cycling. However, he is better known for his impressive thighs than for his titles. They measure between 74 and 78 centimetres in circumference. That is roughly equivalent to a 100-kilo weight plate - and his legs "have a lot of power", he says. Even if Förstemann is an absolute exception: every cyclist wants strong legs, regardless of the discipline. After all, they do most of the mechanical work in the saddle.
The power cycle
Within the leg muscles, however, not all muscle groups play the same role - or work at the same time. "Electromyography is a very good way of finding out which muscles are involved in the pedalling rotation and when. Accordingly, there are good scientific analyses of muscle activity during the pedalling process," explains Björn Geesmann. The sports scientist heads HYCYS, the largest privately run scientific institute for coaching, performance diagnostics and bike fitting in Germany, which has worked with World Tour teams such as Alpecin-Premier Tech and Red Bull-Bora-Hansgrohe in recent years.
"The greater part of the power is generated in the downward movement," explains the expert. This is the crank position 0 to 180 degrees. This phase, in turn, can be divided into the early pushing phase, in which the quadriceps and rectus femoris thigh muscles do the main work. In the later pushing phase, the gluteus maximus, the large gluteal muscle, is more involved, with support from the hamstrings, the muscles at the back of the thigh. The activity therefore shifts from the front to the back and from the knee to the hip. In the first compression phase, the knee extensor at the front carries more weight than the knee flexor at the back. The lower dead centre that follows the push phase is not so dead: here the hamstrings and the two-headed calf muscle (gastrocnemius) accompany the transition into the pull phase. In this return phase, the hip flexor and the anterior tibialis muscle work more intensively.
The difference between amateur and professional athletes
"That's a bit of a simplification, of course. Muscle activity is not strictly divided into phases, but runs in parallel. The muscles work simultaneously, but with different weighting," says Björn Geesmann, who also knows that the activity of the muscles depends on the level of performance: "Even in well-trained amateur athletes, the gluteus is less involved in the pedal rotation, whereas professional athletes have a very pronounced large gluteal muscle," he explains. One of the reasons for this is probably that this muscle is used in a completely different way with a low sitting position and training times of five, six or more hours per day and professionals often learn to actively control the gluteus over the entire pedalling cycle. Amateur riders, on the other hand, often generate power mainly via the quadriceps.
Uphill with power
The ability of the nervous system to activate muscles in a targeted manner via impulses is called neurological activation. It determines the coordination, speed and efficiency of movements and also plays a role on long uphill rides in particular; the more fatigued you are, the more important it is. This is because if neurological abilities and intramuscular coordination deteriorate, the muscles - in this case primarily the knee and hip extensors - are less controllable and the cadence becomes lower. On climbs, however, the latter is one of the factors that determines performance. Power is the product of strength and cadence. "If you want or have to change the cadence for the same power output, let's say from 90 revolutions per minute to 60, you have to apply a significantly greater amount of force to maintain the same power output because the cadence is lower," summarises Björn Geesmann. More effort means greater muscle strain and faster fatigue, while less effort relieves the muscles and improves blood circulation through their rapid contraction and relaxation cycles.
Downhill with attitude
Downhill, on the other hand, the muscles stabilise rather than actively generate power. In particular, muscles that are primarily active in the return phase, such as the hip flexors, play a subordinate role here. On sloping terrain, the thigh muscles in particular, but also the calves and the muscles around the hips and torso are required. They absorb vibrations and shocks and help to maintain your position on the road bike. "Muscle activity here is more dependent on external influences such as the surface and riding technique. As far as I know, however, there is no scientific work that deals with the exact muscle activity in the upper body when riding downhill," adds sports scientist Geesmann.
Not all power is the same
Within muscular performance, different forms of strength can be distinguished.
- Maximum strength describes the greatest possible force that a muscle can generate, regardless of time. It is required on short, steep climbs, for example. Type II muscle fibres (fast twitch) are mainly active here.
- Speed strength on the other hand, refers to the ability to develop strength as quickly as possible, for example during (target) sprints. Type II fibres are also dominant here.
- Strength endurance is particularly relevant for road cycling. This is the ability to deliver a certain performance over a longer period of time without it dropping significantly. This requires slow-contracting type I muscle fibres (slow twitch).
Capillary capillaries
A certain level of performance is also required for long tours or marathon races. However, this is not defined by the maximum force applied to the pedals. Thick muscles are not the decisive factor here. Rather, a solid endurance performance results from an optimal energy supply - consisting of a good VO2max, among other things. This parameter describes the body's maximum oxygen uptake capacity and defines the maximum amount of oxygen we are able to process in the muscles and convert into propulsive energy.
A central element here is the cardiovascular system. In contrast to the system of an inactive "couch potato", an efficient cardiovascular system is characterised by a high stroke volume of the heart. This means that more blood is transported per heartbeat. The more blood the heart pumps per beat, the more oxygen reaches the working muscles.
At the same time, the capillary density in the muscles is increased in people with a high VO2max. These are the finest blood vessels that supply the muscle tissue. If there are many capillaries, the muscles can process more oxygen and nutrients and remove waste products better. Performance increases. "Adequate fat metabolism and a good energy supply are also necessary for sustained good endurance performance," adds Björn Geesmann.
Fuel for sprints and marathons
This is because muscles cannot work without energy. The main sources of energy during sporting activity are carbohydrates. These are quickly available in the body, but to a limited extent. Fats are also available as an energy source. They are slower to supply, but provide virtually unlimited power. Three different metabolic processes help people to convert this energy into propulsion on the bike. All three are always active, but are utilised to different degrees depending on the duration and intensity of the exertion: the alactacid, lactacid or anaerobic and aerobic systems. They all provide ATP, an energy source that the muscles need to contract. Because without muscle contraction, there is no locomotion.
"The alactacid system utilises high-energy phosphates. It is the most efficient and very fast, but also extremely limited. The phosphates are used up after just a few seconds. More than a short sprint is not possible," explains Björn Geesmann.
Energy systems
The anaerobic system is also comparatively efficient, as it provides energy without oxygen. To do this, it breaks down sugar molecules. However, not completely, which is why less ATP is produced and more lactate accumulates. "The anaerobic or lactacid system is active at high intensities, but is exhausted after a few minutes. The limiting factors here are the carbohydrate consumption associated with prolonged exercise and the possible over-acidification of the muscles if too many anaerobic peaks follow one another or the recovery time is insufficient," says the sports scientist.
The aerobic system therefore does most of the work during prolonged exercise. Here, energy is obtained from carbohydrates and fats using oxygen. This process is slower, but much more efficient and sustainable. However, it is not self-sustaining: In contrast to fat, which is available almost indefinitely even in well-trained athletes and therefore does not need to be replenished during exercise, the situation is different with glycogen. "We need replenishment in the form of carbohydrates in order to have sufficient energy available for muscle contraction over long periods of time," explains Björn Geesmann.
Those who refuel earlier are faster for longer
The stores of glycogen - the storage form of carbohydrates in the muscles and liver - are limited. If you want to avoid running out of fuel, you need to refuel on the way - and early on: "It makes no sense not to eat any carbohydrates in the first few hours of exercise just because you think there are enough in your muscles. The point is to conserve these stores and only nibble at them towards the end, or to help yourself to a mix of exogenous, i.e. externally supplied, and endogenous carbohydrates," explains Björn Geesmann.
He considers between 60 and 90 grams per hour with a 1:2 ratio of fructose to glucose to be a good approach for hobby and amateur athletes that is feasible with a little familiarisation. Fats and their intake only become more important during extremely long periods of exertion, such as an ultra race, as "at some point it is no longer just a question of providing carbohydrates, but of providing energy and avoiding an energy deficit in general. For example, during an exertion lasting several days".
In addition to these macronutrients, some micronutrients are also relevant for performance. Electrolytes such as sodium, potassium and magnesium are crucial for nerve and muscle function. A loss through sweat can impair performance, especially on long or intensive journeys, says Björn Geesmann. He advises: "Minerals such as sodium are important for the ability to absorb water and therefore for thermoregulation and muscle function. It makes sense to replace the loss, for example with a sports drink, if the exercise lasts longer than 90 minutes, is intense or the weather is hot." So feel free to add a little table salt or an electrolyte tablet to the drink in your bike bottle.
