When we talk about power we can also talk about the movements that we can perform to increase our ability to produce force in a given movement. By referring to muscle preload, we refer to the movements that we can perform to activate the muscles before muscle contraction. This preload or countermovement is important because previously activated muscles generate more force than muscles that simply contract.
A clear example of a movement with a preload can be the jump. If we ask an athlete to jump as high as he can, what he is likely to do is a countermovement jump, and not just a leg jump.
The jump with counter movement always wins
Even with an equal force capacity in each leg, more height will be obtained in a jump with countermovement than if we do a jump without countermovement. Athletes can normally jump 3-6cm higher with a counter-motion jump than without a counter-motion jump. Most people know this instinctively, even if they have never studied physiology or biomechanics.
One of the reasons you gain more height with a counter-motion jump is due to a characteristic muscle physiology called the Stretch-Shorten Cycle.
How does the stretch-shortening cycle work
The Stretch-Shorten cycle consists of the combination of an eccentric contraction that immediately follows with a concentric contraction (CC), with which an improvement of the work produced is achieved thanks to the myotatic stretch reflex and the muscular elasticity or capacity of the muscle to store elastic energy during stretching and partially utilize it in a contraction performed immediately afterward. For this reason, the jump with counter movement can generate more height than a jump without counter movement. The participation of these factors entails mechanical efficiency, as a higher height is achieved in a vertical jump preceded by countermovement than in a jump without countermovement (Asmussen, 19741 González and Gorostiaga, 1995; Bobbert et al, 1996) and greater electromyographic activation ( 35%) of the muscles involved (González and Gorostiaga, 1995), without causing a greater energy expenditure (Cavagna, 1965, Cavagna, 1968, cited by González and Gorostiaga, 1995; Gómez, 1997).
Counter-movement in cross-country skiing
Normally, when cross-country skiers talk about a “preload” they are talking about counter movements that pre-activate the muscles of the legs and arms to give them more strength to perform the movement they want to perform and can be applied for both techniques of skiing. background.
For example, the triceps are often preloaded when the poles come into contact with the snow. If the contact of the tip of the poles with the snow is with sufficient force, the arm is flexed at the elbow joint and the body is propelled by extending the triceps just before its contraction during the push of the poles.
Pre-loading or counter-movement of the leg muscles in cross-country skiing
We are going to focus on the preload of the leg muscles during the kick in the classic style (the kick is the push of the leg). In the classic style the leg pushes down and back, in the skater style the push is down and to the side.
When we watch cross-country skiers talk about bearing weight, both in classical technique and in skating technique, they are talking about the push-down action at the start of the leg push. This pre-load or weight-bearing is similar to what happens in the countermovement jump, when you flex abruptly to a crouch, flexing the ankle and knee joints. If we observe the movement of the jump well, we will notice that the leg flexes and then extends during the push phase to give us the impulse of the body upwards. This is also applicable if we observe the movement of the cross-country ski but the objective is to move our body forward.
As we have already mentioned, this load of the weight on the ski pre-activates the muscles of the legs to generate more force. In cross-country skiing, but especially in the classic technique, the load of the weight or pre-load is even more important since it serves to overcome the bridge of the ski on the snow and in this way to be able to achieve a grip on the snow to perform the impulse.
In two of the techniques of the classic style, the alternating step and the double pole with impulse, the pressure on the ski is decisive to be able to propel ourselves. If this counter movement prior to the impulse is correct we will be able to carry out these two steps properly.
Exercises to be more effective in bearing weight
- Straighten the leg while the ski is sliding. One of the things we may have noticed is that cross-country skiers frequently extend their support leg during the glide. This leg extension movement is because the athlete seeks to increase the leg travel and attempt to load the full weight of their body before the push.
- Exaggerate the flexion of the knee and ankle as well as the pressure on the skis. Trying to load our body weight too much and exaggerating the flexion of the joints involved can give us the feeling that we need to experiment to achieve correct technique.
- Jump on the skis. This is an option to be able to correctly transmit the weight in each step, but it does not have to be incorporated as a technical movement.
- Ski without poles. Practice without poles is ideal not only for beginners, even professional athletes of the best level always carry out technical ski work without poles, either to correct technical gestures or to carry out specific training tasks.
In summary:
- The pre-load or countermovement is the first part of the leg push movement.
- A heavy load is required on the ski to be propelled in order to overcome the bow of the ski.
- The correct load of the weight of the body pre-activates the muscles of the legs and gives us the grip on the snow to be able to push ourselves effectively.
- Ankle and knee flexion is essential to achieve a correct pre-load.
- If this weight bearing thing sounds complicated and you wonder if it is something that I will be able to learn, remember this: “Pre-loading your muscles with a counter movement is something you already know how to do, you just have to learn to apply it on skis” .
Bibliographic references
- Eccentric Exercise: Physiology and application in sport and rehabilitation.
- González, J. Gorostiaga, E .; Training basics of the strength. Inde, 1995.
- Bosco, c. “Physiological considerations on strength, blast power, and jumping exercises.” Eurovolley Magazine, 1982 nº1 and 2.
- Bosco, C. Komi, P .; Influence of aging on the mechanical behavior of leg extensor muscles. European Journal of Applied Physiology, 1980, 45, 209-219.
- Bosco, C. Luhtanen, P. Komi, P; A simpled meted for measurement if the mechanical power jumping. European Journal of Applied Physiology, 1983, 50, 273-282.
- González, J. Gorostiaga, E .; Training basics of the strength. Inde, 1995.
- Hakkinen, K .; Muscle cross-sectional area and voluntary force production characteristics in elite strength, and endurance trained and sprinters. European Journal of applied Physiology, 1999, 59, 215-220.
- Komi, P .; Bosco, C .; Utilization of stored elastic energy in leg extensor muscles by men and women. Medicine and Science in Sport, 1978, 10, 261-265.
