The tandava dance involves fast ballistic joint motions and high force generation in the lower extremity muscles. Certain jumps in tandava are used in plyometrics like the tuck jump, heel to butt jump and squat jump. Plyometrics is a type of training to increase power, strength and speed in movement. These jumps are quick powerful movements involving an eccentric contraction immediately followed by a powerful concentric contraction. This sequence is referred to as stretch - shortening cycle (SSC). Muscles have a spring-like property where energy can be stored and transferred. When a muscle is lengthened, energy is released as heat, but some energy is stored in the muscles and tendons to be used in its subsequent contraction. A greater jump height is observed when SSC mechanism is activated (Kurokawa et al, 2003) Eccentric contraction is a lengthening contraction normally active during lowering of a limb whereby control is needed to counter the effects of gravity. Concentric contraction involves shortening of the muscle.

These movements stimulate the body's nervous system. As was mentioned, fast ballistic joint motions are involved and therefore will require a specific fast twitch (FT) muscle to perform the action. And in the body, the muscles used for jumping are predominantly FT type. But not everybody is endowed with the same amount of FT fibers in the same muscle. So does that mean that the person with less FT fiber loses out? Not at all. It all depends on the efficiency of the nervous system as to how fast it can call on all available motor units to contract within the time frame of the ballistic motion. A jump takes 2 seconds while ordinarily an average person can only recruit 50% of the available motor units in 4-6 sec. So if the nervous system is capable of recruiting nearly all of the FT fibers then they will tend to have a superior performance and the more one trains, the efficiency of the nervous system improves. Therefore, tandava dance is indeed invigorating.

                          

            Fig 1                                                               fig 2

Dancer begins with body weight balanced on the toes with arms stretched out to sides reinforcing the balance (fig 1). Standing on balls of the feet will load the plantar flexors isometrically. It will result in better stability of feet on landing and greater reduction in forces in the heels on landing. (Jahnsen, 1996). The paraspinal muscles of the back are contracting isometrically to stabilize the vertebral column. Propulsion is generated from a slight push from the ankles, calves, knees and hips. A push through the surface from the balls of feet will finally propel the dancer into flight. A slight knee bent before take off utilizes the stretch - shortening cycle (SSC) where there is a preliminary downward movement by flexing the knees and hips and then immediately extending the knees and hips again. Knee extensors will fire strongly to stop the downward movement and to start the push off. The elastic energy stored in the tendinous components of these pre stretched muscles will give a considerable amount of energy at take off thereby increasing the force of their subsequent contraction. The muscles that are pre-stretched are the hip extensors, knee extensors, the plantar flexors of the ankles which are situated on the back part of the lower leg. The plantar flexors extend the foot downwards. The plantar flexors are gastrocnemius, soleus, toe flexors, Tibialis

                                                      

                                                      Fig 3 muscles of the lower extremity

Posterior and the peroneii. Hubbley et al (1982) reported that average relative contributions of the ankle, hips and knees muscles were approximately 23%, 28% and 49% respectively during maximal vertical jump motion. At the ankle, almost half the work is done by the gastrocnemius muscle. The stress across the knee joint is about the 24 times the body weight. (Palastanga, Field &Soames, 1994).

While airborne, dancer strongly bends his knees (fig 2), forcefully pressing the heels towards the butt in the air via the concentric contraction of the hamstring muscles. By bending the hips the efficiency of the hamstrings as knee flexors increases due to its pre stretch tension generating properties. There is a co - contraction of the hip extensors and flexors to stabilize the hip joint during this forceful knee bend motion. Now dancer is making preparation to land on the toes into the deep squat position. The knees will have to straighten to bring the feet forward to prepare for landing which is the work of the eccentric contraction of the hamstrings.

At the terminal airborne phase series of neuromuscular activities unfolds. Pre-landing muscle activity plays an important role as it must prepare the muscle tendon complex for a rapid forceful stretch occurring after foot contact and throughout subsequent joint rotations. Many authors concur that there is increased activity in knee extensors and flexors, Tibialis anterior, peroneii and gastrocnemius - soleus complex but more pronounced in the ankle joints as demonstrated by a co-contraction of soleus - Tibialis Anterior (back and front muscles of the ankle joint) at the ankle joints occurring before and after touchdown which is a spinal reflex triggered by ankle joint rotation. This co-contraction mechanism is responsible for increasing ankle joint stiffness to assist with force absorption. As the toes impact the ground, there is simultaneous hip and knee flexion. Landing on toes in the bent hips, knees and ankles position (fig 4) help spread out the impact on landing but muscle work is greater across the hip joint in the deep squat landing position as compared to landing in the erect posture. The landing involves the delicate placement of feet which requires a high degree of kinesthetic awareness of the joints in space. This phase develops balance while making subtle neuromuscular adjustments that prepare the body for its subsequent loads. Marco Santello, an expert on Biomechanics on jump landing and EMG from Arizona State University summarized in his 2005 literature review in Gait & Posture that prior to foot contact, there is co-activation of the muscle fiber motor neuron and muscle spindle which leads to the modulation of the reflex muscle activation throughout the stretch of the muscle-tendon complex (fig 5). It further deduced that in post landing that is after the feet strike the ground that reflex mechanisms possibly overlaps with the greater central control of muscle force during ballistic joint motions. In another study, he inferred how visual, vestibular (a balancing organ) and proprioceptive information is integrated to allow a safe and effective absorption of kinetic energy after touchdown.

                                      

            Fig 4 deep squat                   Fig 5 Muscle reflex action                           

Next, dancer will jump up again from deep squat position almost immediately after landing and bring the knees toward the chest. The predominant feature of jumping from a deep squat position is that there is primarily isometric loading of the knee extensors. This allows for adaptation of the muscle spindles (structure within the muscle belly which is stretch sensitive leading to regulation of muscle tone) during the loading and resulting in increased sensitivity during landing. Consequently the knee muscle will require shorter time to stabilize the knee joint. The biomechanics of the take off has already been discussed except that taking of from a deep squat position does not utilize the SSC. The muscles of the thighs, buttock and plantar flexors are stretched too long that there is very little elastic energy stored in them. Hip and knee extensors and plantar flexors will extend the respective joints followed by a strong concentric contraction of the hip flexor muscles with a simultaneously lengthening of the seat muscle to tuck the knees towards the chest. The antagonist muscle reflex will have to precisely timed to inhibit any seat muscle contraction (fig 5). The abdominal muscles help stabilize the pelvic girdle during this maneuver by counteracting forward tilt of the pelvis as the hip flexors pull onto the lumbar spine. Consequently, a stable pelvis acts as the firm base upon which the hip flexors move the legs explosively at the hip joint. With the hips going into flexion, the hamstrings again become a better knee flexor resulting in the knees to chest position. From this position, dancer will extend the lower limbs and once more prepare to land with knees bent to absorb the impact as feet land flat on the ground. The final posture is erect. 45% of the muscle work is across the knees while 40% is across the hips in a flat feet landing. The foot is now rigid again to withstand the weight bearing forces and Tibialis posterior and soleus muscles will contract to control the feet arches from flattening too much as the impact on loading will certainly jam the  arches flat without any muscular control.

Dancer will then raise alternate bent leg crossing the midline of the body towards the opposite arm pit (fig 6) with a rhythmical opposite flat foot and high leg lift- foot flat-foot spring-flat foot accompanied by opposite high leg lift. These are single leg jumps which means that there is increase force in the muscles of the jumping leg (muscle velocity in the single leg jump will be lower as compared to a double leg jump).Moreover, the body weight is now distributed over one leg so the muscles will have a higher active state of contraction at the start position (Bobbert et al, 2006). Prior to the leg lifts, there is pre-innervation of the core stability muscles provided by the deep abdominals as well as the

 Fig 6

deep back muscles to support the spine and pelvic girdle. The mobilizers of the trunk namely the abdominal obliques will contract isometrically to further stabilize the erect torso thus enabling the leg to forcefully flex as worked by the hip flexor  and adduct (crossing mid line of the body) as worked by the adductor muscle (situated on the inner thigh). All the muscles on the stance leg will work isometrically to hold the body up in space and particularly the lateral hip muscle to avoid an opposite drop of the pelvis. This continues for as long as the sequence continues.

The mechanics of the concluding part of the dance is as previously discussed.