Monday, September 16, 2002 - Physiology
Cross Country Ski Specific Core Strength And Stability Program (Part 1 of 4)

- By: Ross McKinnon, PT

There has been much attention to the idea of ‘core strength’ in all sports in the past few years. Pete Saar in 1997 outlined a core strength program for cross country skiers. This article will outline a comprehensive ski specific core stability and strength program based on the latest research and understanding of the core musculature. Core stability and strength are especially important for cross country ski racing as the two techniques require muscles to work in different planes of movement. Core strength should not replace, but enhance, general or ski specific strengthening exercises.

The advantages of a well planned core strength and stability program are numerous:

  • Improved performance by providing a stable base from which the lower and upper extremity muscles can increase power.
  • Maintain technique and balance when fatigued.
  • Reduces existing muscle imbalance and potential injury.
  • Many lower and upper extremity injuries, not just back pain, can be linked to muscle imbalance and poor stability of the core
  • .

    Muscles are broadly divided into stabilizers and mover/power muscles (i.e. rotator cuff and deltoid). Movers are the muscles that provide the power for sport performance. Stabilizers are the muscles that provide the control during these movements. All muscles provide power and stability, however each muscle is designed to be most efficient in one role. Both systems must work together for optimal efficiency. For example; a door hinge needs firm connection to both the frame and door to operate correctly. If the screws connecting the hinge to the frame are loose the hinge will never operate correctly.

    Stabilizers
    • Cross one joint
    • Short lever arm
    • Broad insertion to distribute load
    • Leverage for load maintenance, static holding
      and joint compression
    • Associated with eccentric deceleration
    • Optimally assist with posture holding
    • Greater recruitment of slow twitch fibers
    • Trained with low load exercise
    Movers
    • Cross more than one joint
    • Long lever
    • Unidirectional fibers or insertions to direct force
    • Leverage for range, power and speed (high force production)
    • Associated with rapid and repetitive movement (acceleration)
    • Greater recruitment of fast twitch fibers
    • Trained with high load exercise
    (From Comerford and Mottram 2001)

    REMEMBER that with any muscle action slow twitch muscle fibers will be recruited prior to fast twitch muscle fibers. This is very important as the slow twitch muscle fibers (stabilizers) must work correctly and efficiently to allow optimal recruitment of faster twitch muscles. Poor strength results in weakness and decreased performance. Poor stability results in poor motor control, the development of muscle imbalance and eventual injury. Table 1. Strength and stability comparison.
    (From Comerford, 2001)

    Good Stability Poor Stability
    Good high performance poor performance
    Strength pain free pain

    Traditional strengthening and core strength programs focus on the mover/power muscles. However it is critical that the stability muscle system must first be functioning properly for optimal sport performance and injury prevention. Strength training is crucial to improve ski performance but an athlete must first be able to control movements through correct use of the stability system. THE ABILITY TO CONTROL MOVEMENTS AND THEREFORE OPERATE AT MAXIMAL PERFORMANCE WILL RARELY IMPROVE WITH STRENGTHENING EXERCISES ONLY.

    In summary, emphasis on strength training is not effective to improve performance if there is existing muscle imbalance and poor stability in the musculoskeletal system. Strength exercises target the power/mover muscles. Focusing on strengthening the mover/power muscles will typically not correct muscle imbalance rather it will result in further compensation. While strengthening exercises require a certain degree of stabilization it is commonly the incorrect muscles that try to provide the stability when muscle imbalance exists.

    A strength and stability program should address the following areas.

  • Core stability exercises
  • Core strengthening exercises
  • Flexibility exercises for the core
  • Balance exercises
  • Breathing exercises
  • POSTURE

    The Kendalls (physiotherapists) have documented both ‘ideal’ and three common postural variants: Kyphosis-Lordosis; Swayback; and the Flat back posture. Each postural type is associated with muscle imbalance. The dominant postural pattern is cross-country skiers appears to be varying degrees of the ‘ideal’ to swayback posture.

    Our posture and alignment are primarily the result of the way the body has been used over a prolonged period of time. Prolonged postural holding and/or repetitive activity will result in adaptive changes in muscle length and therefore muscle recruitment. An in depth postural analysis is not required by a coach or an athlete, rather a basic understanding of how postures can affect muscle imbalances. It must be kept in mind that an athlete’s ski posture or technique may not represent the exact static position. However an athlete’s resting posture gives clues as to existing muscle imbalances that can be addressed with proper exercise.

    Typically the power/mover muscles will become tight and short, i.e. the muscles that always feel tight and need to be stretched. In fact they are overworked as they are trying to provide stability and power due to ineffective local stabilization. The power/mover muscles then are less effective to generate force as they have become increasingly used for stability (the ideal length/tension relationship is altered). Stability muscles will lengthen and become weak resulting in ineffective control as well as altered timing and recruitment.

    Ideal Alignment
    A vertical line should pass through:
    • tip of the ear lobe
    • outside tip of the shoulder joint
    • slightly forward of the thoracic vertebrae
    • through the bodies of the lumbar vertebrae
    • slightly behind the hip joint
    • slightly forward of the knee joint and ankle
    Sway back characteristics
    • forward sway of the pelvis ahead of the center of gravity
    • (KEY CHARACTERISTIC)
    • neutral to posterior tilt of the pelvis
    • thoracic kyphosis increase in length
    • lumbar lordosis decrease in length
    • Oblique abdominals long and weak, rectus abdominus – overactive or short
    • Back extensors – long and inhibited through midback
    • Gluts and Iliopsoas –long and inhibited
    • TFL and Hamstrings – short and overactive

    STABILITY EXERCISES

    THE INNER UNIT
    Stability of the trunk or ‘core’ requires two muscle systems to work in unison. The two systems are called the inner and outer units. The inner unit consists of the multifidus, transverse abdominus, diaphragm, psoas major, the pelvic floor and diaphragm. Too isolate the inner unit the following instructions are followed: (this is best taught by a physiotherapist)

    The athlete should lie on their back with their hips and knees bent. The athlete should place both their hands on their stomach approximately 3cm down and in front of the anterior crest of the pelvis. The natural curve of the spine must be maintained. The athlete is instructed to “draw the belly button into the spine”. The front and lateral aspects of the abdominal wall should lead the contraction. There should be no tilting of the spine or pelvis, any upper abdominal tension, any internal oblique bulge, rib cage elevation, or breath holding. The athlete is to maintain this position for 10 seconds 10 times with normal rib cage breathing. This isolation requires <25% effort and is not a maximal effort. See assessment for further details.

    (Redrawn from Lee 1999)
    THE OUTER UNIT

    This stability system consists of 4 groups of muscle slings and the interconnecting soft tissue
    1. Posterior oblique system
    • Latisimus dorsi
    • Gluteus maximus
    • Thoracolumbar fascia

    (Redrawn from Lee 1999)
    2. Deep Longitudinal System
    • Erector spinae
    • Thoracolumbar fascia and pelvic ligaments
    • Hamstrings
    3. Anterior oblique system
    a. External and internal obliques
    b. Opposite side hip adductors
    c. Thoracolumbar fascia
    4. Lateral system
    d. Gluteus medius and minimus
    e. Opposite side hip adductor

    (Redrawn from Lee 1999)

    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 one of his weekly four part series on cross country ski specific core strength and stability.


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