Ai Chi is known as a relaxation technique. The ICF does not define relaxation in the musculoskeletal domain, but refers to:
- Mobility of joint functions: Functions of the range and ease of movement of a joint.
- Mobility of bone functions: Functions of the range and ease of movement of the scapula, pelvis, carpal and tarsal bones.
- Muscle tone functions: Functions related to the tension present in the resting muscles and the resistance offered when trying to move the muscles passively.
- Sensation of muscle stiffness: Sensation of tightness or stiffness of muscles.
- Sensation of muscle spasm: Sensation of involuntary contraction of a muscle or a group of muscles.
These categories refer to pathological variations in the function of connective tissue (CT): abnormal shortness or diminished mobility, both from a mechanical and from a sensory point of view. The ICF mentions range and ease of movement. Clinically stiffness in an existing range of motion can be altered or the range of motion can be increased in case of a reduction of mobility.
Connective tissue is found in muscles, tendons, aponeuroses, capsules, periarticular fascia, discs and within the nervous system. Important elements of connective tissue are the collagenous fibers and the ground substance. Stiffness in muscles also includes a contractile element and will be included in this paragraph. Lengthening of connective tissue that may be abnormally restraining osteokinematic motion is an important objective in aquatic therapy, also referred to as stretching, elongation or mobilization.37,38 Various techniques exist to address connective tissue of muscles (e.g. PNF stretches39), connective tissue around joints
(e.g. Kaltenborn / Evjent40) or connective tissue of the nervous system (neurodynamics by Butler41 and Shacklock42). One can differentiate between addressing collagenous fibers and it’s cross-links and the visco-elastic behavior of the ground substance. Mobility increase therefore can include9,43,44 :
- breaking (excessive) cross-links between adjacent CT bundles
- achieving plastic deformation of CT fibers through tissue restoration after micro-tears
- stress-relaxation and creep of collagen fibers
- thixotropic decrease of actin-myosin cross-bridge stiffness
- restoring the interstitial fluid component to normal levels
Connective tissue has viscoelastic properties that are affected through length and through the velocity of movements. Connective tissue that is loaded more quickly will behave more stiffly (deform less) than the same tissue when loaded at a slower rate. The viscosity of the ground substance gives resistance at the beginning of an elongation. The ground substance can be altered more easily by slow movements. The ground substance has a property which is called thixotropy. This means that movement can reduce viscous stiffness (like stirring paint). The ground substance consists of a large percentage of water, bound by glycoproteins and acting like a gel. One of the functions of this gel is to stabilize and steer collagenous fibers. Immobilization decreases the amount proteoglycans and deteriorates the function of the collagenous fibres by increasing inter-fiber friction and reducing alignment. Movement therefore is important. With a biological half time of just a few days of repetitive movement function of the ground substance can easily be improved. Repeated movements have measurable effects on stiffness or resistive torque, even decreasing during the first 3 repetitions.45 This reduction in resistance to movement also affects hypertonic muscles in stroke patients and has been attributed to thixotropic effects.45 Immersion is known to create a fluid shift from cellular and interstitial compartments to the vascular space.46
Somato-visceral reflexes can positively influence visceral activity. The sympathetic system originates from the spinal cord segments C8-L2. Afferent (mechano)sensory information through movement without pain in these segments will inhibit efferent sympathetic activity. Ai Chi focuses in trunk movements (in order to stretch meridians) in the thoracic-lumbar area and might therefore inhibit sympathetic activity. Research discussed in Chapter 2 has found a reduction in sympathetic activity during warm water immersion, which may play a role as well.
When an agonist muscle is contracting concentrically, antagonists elongate. Passive mechanical properties of the muscle play a role in the initial stiffness or tension of an elongation, like muscle filament resting tension because of actin-myosin cross-bridges47 and the short range elastic component.48 These properties are temporarily reduced by prior movements, but depend on the velocity of these movements as well. Tension decreases with a decrease of velocity, which is a thixotropic behavior (movement affects viscosity). This means that movements should be slow in order to decrease the force required to overcome musculotendinous stiffness.
Visco-elastic characteristics are a temperature-dependent variable. The higher the temperature, the more pronounced the viscous properties of connective tissue reducing dominance of elastic properties with tension rapidly reducing under lengthening conditions . In vitro experiments by Lehman49 showed progressive reduction in elastic properties as waterbath temperatures increased from 35.6ºC to 45ºC. In vivo research has shown that immersion in 40ºC increases extensibility of the hamstring muscles significantly because of changes in viscoelasticity,50 measured with the straight leg raising test. Also immersion in 32ºC significantly increases ROM and decreases stiffness, measured with the modified Ashworth scale in children with CP compared to immersion in 29ºC.51
The results of effects of immersion and aquatic therapy on stiffness are mixed. Verhagen52 and Bartels53 did not find statistically significant differences in stiffness, measured with the Womac, in their Cochrane reviews on balneotherapy and aquatic exercise of knee and hip osteoarthritis respectively. Verhagen52 reported the same negative outcome in their review on balneotherapy in rheumatoid arthritis.54 Jentoft55 however found significant stiffness changes after aquatic therapy in persons with fibromyalgia.
In order to make a mobilizing and stretching technique like contract / relax antagonist contractions effective, only 20% of the maximal voluntary contraction is necessary.56 The mobilizing effect on connective tissue is supported by the fact that Ai Chi movements are performed with reduced force. Ai Chi includes slow movements such as Uplifting or abduction (in the scapular plane), when an arm covers 180º during a fill breath cycle. When a person is breathing 15 times per minute requires 4 seconds per cycle. This equates to an angular velocity of 45º per second. Muscular activation at these velocities is clearly reduced. Kellyand coworkers compared muscle activation of 6 rotator cuff and shoulder synergists during 3 different speeds of elevation in the scapular plane (30º/s, 45º/s and 90º/s. 57 For all 6 muscles tested, muscle activation during the 30º/s and 45º/s test speeds was significantly less when performed in water versus when performed on land. For example, electromyographic activation of the supraspinatus muscle was 17.46 % of a maximum voluntary contraction (VMC) when elevation was performed at 45º/s on dry land versus 5.71 % when performed in water. Clinical Ai Chi might therefore support early active motion in postsurgical or injured shoulders.
Other kata’s like Gathering include 10 to 12 seconds isometric contraction of shoulder muscles in 1 arm while the other moving (with 3 repetitions). Fujisawa et. al. electromyographically measured 9 parts of 6 shoulder girdle muscles in 9 positions and found that almost all muscle activity in water decreased remarkably in water compared to land.58 For example, during an isometric supraspinatus activity in 90º of abduction, a remarkable reduction of electromyographic activation could be measured from 22.3% of the VMC on land to to 3.9% of the VMC in water. Although the activity of the infraspinatus muscle decreased, the authors suggested that careful attention must be paid to maximal external rotation in early rehabilitation of shoulder surgery or injury because of the relatively high resultant percentage of activity.