How the athlete's body works Part 1: How bikers develop strength and endurance

To move forwards on the bike, your legs have to circle. But which muscles exactly are active? For all those who missed the link to mountain biking in biology lessons, we explain in this article how strength and endurance are created in the body.

Without strength in the legs and endurance in the system, no cyclist can go far and certainly no professional can reach the podium. 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 on average. 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 biker 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 athletes such as former Swiss Epic winner Reto Indergand 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. 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.

"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.

Strong up, stable down

The ability of the nervous system to specifically activate muscles via impulses is called neurological activation. It determines the coordination, speed and efficiency of movements and plays a particularly important role on long uphill rides; the greater the fatigue, the more so. 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, 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 bike. "Muscle activity here is more dependent on external influences such as terrain 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 during downhill riding," 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, for example, on short, steep climbs or when riding over roots. 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 mountain biking. 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

Long tours or marathon races also require a certain level of performance. 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, among other things, of a good VO2max. 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.

Conclusion

Bikers who want to achieve something in their discipline do not need to have studied sport. Nevertheless, it can't hurt to know about your own body. Only those who know the processes in the muscles and the role of the cardiovascular system can work on deficits, organise their training efficiently and improve their performance in a targeted manner. - Jan Timmermann, BIKE editor