Monday, September 23, 2002 - Physiology
Cross Country Ski Specific Core Strength Training (Part 2 of 4)

- By: Ross McKinnon

Part 1

Myths and misconceptions
  • It is not appropriate to eliminate the hip flexors or TFL in trying to isolate the abdominal muscles. There is no biomechanical basis for the isolation of rectus abdominus in core exercises.
  • Bent leg sit ups do not inhibit the hip flexors. Touching the toes together does not inhibit tensor fascia lata (TFL). Instead this makes them work harder in an inner range position. This results in overactivation and shortening. The only advantage of bending the hips is that the hip flexors cannot pull the pelvis into an anterior tilt.
  • Digging the heels in to activate the hip extensors will not inhibit the hip flexors, as well this is non functional and may result in shortened hamstrings.
  • Holding the feet down shifts the role of the exercise away from the abdominals to the hip flexors, again resulting in over activation.
  • Straight leg sit ups if done correctly are safer than bent knee sit ups. If done incorrectly they are potentially damaging to the lower back. Bent knee sit ups produce more flexion strain to the lower back than straight leg sit-ups. Fast crunches are not better. If sit up type exercises are to be done performing them slowly will result in better muscle control and endurance.
  • Sit ups with rotation are not the best way to train the oblique abdominals. A better way to strengthen the obliques and reinforce their role in stability is the lateral abdominal and side trunk raising progressions outlined in the exercise section. These exercises are more functionally related to the role of the abdominal muscles and challenge the muscles in a neutral spine position.
  • Core strengthening exercises are traditionally performed with the lower back flattened to the floor (lumbar flexion), the muscles are therefore strengthened in that position. This is probably not ideal as this position is not ideal for both classic and skating techniques. The core stability exercises should be performed in the neutral spine position.
  • Core stabilization is best emphasized in exercises that involve a rotational challenge.
  • (Adapted from Sahtmann 1999, Comerford 2001, Kendall 1993, Axler and McGIll 1997)

    BALANCED SKIING

    Working to improve balance is often neglected in both dry land and on snow training. The reasons to improve balance are simple; better balance allows the skier to balance on a flat ski more efficiently and improves maneuverability on the ski course, whether it is a flat, a corner or a downhill. Good balance becomes particularly important when fatigued. The ability to weight shift onto a flat ski is necessary as 'edge drag' or a skier's balance adjustments from side to side decreases ski glide.

    We rely on four systems for balance:
    Vestibular system- the vestibular system is a series of canals and chambers in the inner ear that provides information on deceleration and acceleration of the head.
    Visual system- we rely on the information on provided by our edges for spatial orientation and depth perception. We rely heavily on this system for all balance.
    Cutaneous system-The skin contact against our ski boots (especially the sole) provides constant information to the brain on pressure distribution, which in turn helps us balance. Properly fitting ski boot are imperative. If any substantial biomechanical problems exist in the foot and ankle orthotics may be of great benefit.
    Proprioceptive system- Nerve endings in our muscles, tendons and joints provide information on their position which our brain utilizes to analyze balance.
    These four systems provide constant information to our brain. This system is adaptable and can be trained to improve regardless of our ability or age!

    FLEXIBILITY

    The current concepts involving stability and flexibility are as follows:

    The body will take the path of least resistance during movement. Inappropriate motion may be transferred to the site of greatest relative flexibility. This area will show relatively more 'give' than adjacent areas. This may result in cumulative microtrauma and subsequent injury. For example, when we bend forward to touch our toes both the lumbar spine and hamstrings should allow us to bend forward. If the hamstrings are shortened then the lumbar spine will be forced to contribute more to the bending. The lumbar spine then becomes the area of greatest 'give' whereas the hamstrings are restricting movement. A further example is that when we kick during diagonal stride our leg should extend behind the body. If our hip flexors or TFL are short or 'restricted' to achieve the motion we must 'give' in another region, most likely by hyperextending the lower back.

    Habitual movement patterns and postures will result in muscle imbalances. The power/mover muscles will shorten and tighten, whereas the stability muscles will lengthen and become weak and inhibited. For example, if an athlete demonstrates a swayback posture the hamstring muscles will shorten while the gluteal muscles will lengthen and become inhibited. A traditional program of hamstring stretching will do little to change muscle length (the hamstring will continue to support the athlete in standing). Instead retraining the gluteal muscles to assist with standing posture and alignment will allow the hamstrings to lengthen naturally. Furthermore this will improve the skier's performance as the previously inhibited gluteal muscles will increase the ability to generate force. To improve muscular efficiency and balance a proper program of muscle activation and lengthening must be undertaken.

    The first step in attaining stability of the 'give' is achieved by stabilizing the core. The second step is to then lengthen the tight and short power/mover muscles while maintaining control of the 'give'. If the 'give' is not first stabilized, trying to stretch tight and short muscles is ineffective. The body will move though the 'give' prior to the area that truly need lengthening. It is presently thought that lengthening exercises be performed as actively as possible to achieve relaxation of the muscle being lengthened. As you can see this may cause us to rethink traditional stretching exercises.

    Presently there is no information in the sports medicine/physiotherapy literature concerning stretching during adolescent growth spurts. During a growth spurt bones grow faster than muscles. In this case a general stretching program may be of benefit to reduce potential muscle imbalances.

    BREATHING

    The diaphragm is a dome shaped slow twitch skeletal muscle which forms the bottom of the thorax. The diaphragm has a central tendon which is attached to the ribs and vertebrae of the spine. The lungs are roughly divided into the superior, the middle and the lower lobe. As air is drawn into the lungs an increased volume is required. The dome of the diaphragm flattens and is lowered roughly 2cm. At the same time the ribs will expand outward and elevate to increase the lung volume.

    There are three common breathing pattern:
    1) Upper lung breathing uses the neck muscles as primary muscles of respiration which leads to muscle imbalance around the neck and shoulders.
    2) Abdominal breathing the abdominal muscles bulge outward with inspiration. The abdominal muscles are required for posture and stability. This breathing pattern is usually due to posture (increased lumbar flexion), a tight ribcage and thoracic spine. This is often mistakenly called diaphragmatic breathing and is commonly used in relaxation techniques.
    3) Rib cage breathing this is the ideal. This pattern allows the abdominal muscles to provide a stability role allowing for maximal expansion of the lower lobes. Remember that as the diaphragm can only lower 2-3cm. Improving rib expansion will allow more oxygen to enter the lungs (especially the lower lobes where the most oxygen exchange takes place). Posture is extremely important for correct breathing as a flexed or bent posture makes it very difficult for the diaphragm to work correctly. Imagine the diaphragm as a piston; the straighter the shaft the more efficient the piston.

    Ross McKinnon is a former ski racer now working as a physiotherapist at Rutland Physical Therapy in Kelowna, BC. His interests include improving an athletes performance through the use of exercise (both injured and non injured). For further questions he can be contacted at or at . This article is part two of his weekly four part series on cross country ski specific core strength and stability.


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