Forehand

Positioning (open stance vs square stance)
As mentioned in the previous blogs, the importance of balanced stance is in the player’s base of support as it should be wide so the center of mass stays within the limits of the base of support. In any other way, the player is out of balance and the stroke is out of control.
When I’m thinking about the proper positioning for the stroke, I’m always thinking about the square stance. Being at the square stance a player has time for proper loading with the body weight placed at the back toes and right shoulder easily rotated backwards (behind the left). Open stance demands a lot more effort and muscle activity as the rotation of the hip and torso need to be more intense due to the feet positioning. At the contact point the right and left hip should be aligned, but the problem can be that with the open stance a player begins the stroke production from the hip slightly aligned, so this stance would be recommended for the very experienced player that have complete knowledge of biomechanics in tennis. So, the right foot (right handers) should be always behind the left foot as the right foot is the power foot and the left foot is the stability foot. From the right foot, the energy is transferred to the right hip initiating the forward linear rotation through the ball. If the right foot is skipped as the first chain of the energy transfer sequence, the player is losing too much of the free impact force and energy sources from the ground.

Unit turn/Take back
Take back doesn’t include only the rotation of the torso but the whole unit turn. Unit turn begins from the toes and completes with the torso. The point of the take back is to prepare the player for loading or further positioning, if needed.

As soon as player recognizes that the ball is approaching to the forehand side, take back should be done. If the loading is following, the player uses the take back to stretch in full the muscles of the trunk (obliques,  abdiminals, back extensors) while the lower body muscles are loading (gastrocnemius, soleus, quadriceps, gluteals) and create a stretch shortening momentum. If more positioning is needed, the take back should be short having a racquet on the side of the body (not behind) so the player can move efficiently while having upper body ready.
To ensure the complete and powerful take back stretching, both shoulders should be rotated away from the ball which is sometimes not a case. To create the loading of the shoulders, the non dominant arm should be the one taking the racquet to the take back position. There are many benefiting reasons to do so. Firstly by doing this, the non hitting shoulder is definitely rotating away from the ball. Secondly, it makes the hitting arm relaxed as there is no grip pressure. Thirdly, following the shoulder rotation, the muscles of the non dominant side are stretching adding the tension to the whole torso which is needed for the efficient stretch shortening unloading.

Loading
As mentioned in the previous blogs, the sequence of the muscle-joint motions are transferring the energy from the toes to the arm and wrist which is well known as the transfer of energy through the kinetic chain. Kinetic energy and momentum are developed from the legs, hips and trunk muscles and then transferred to the arm and wrist motion. This directs the energy efficiently to the hands, moving the racquet-head with maximum speed to the ball. So the main goal of the loading phase is, after the player has positioned properly towards the ball, to create such a short powerful tension in the big muscles of the body that during the unloading the energy will be distributed from the bigger to smaller muscles and joints creating the stroke. These bigger muscles are the chest (pectoralis), shoulder (deltoids) and abdominal (oblique) muscles at the upper front, serratus anterior, latissimus dorsi and infraspinatus at the upper back. Gluteus and hip extensor muscles as the lower body big muscles (quads and hamstrings as well). The upper body muscles are loaded with the shoulder turn (read about the take back) and lower are loaded by the tilt of the hip, placing the body weight to the rear leg toes.
The body is receiving energy for the kinetic chain from putting the pressure against the ground. It sounds too scientific but it’s something amazing that all the players should be aware of. It’s the free energy that we receive and should be used when walking, running or playing sports. The fact is that this force by the name of IMPACT FORCE is awarding us with free energy every time we get in contact with the ground. So the deal is, the more we apply our body weight to the ground, the ground will reward us back with many times bigger force (when we run is 3-4 times back!). That’s the energy that we should be using when playing tennis and it’s transferred from the toes, leg muscles, hips, torso, arm and wrist muscles. The joints are the ones that are directing that energy and for us to use this amazing amount of energy in the best way possible the joints should be very flexible and injury free (read more about the warm up and stretching!).

Stretch shortening momentum
Loading energy is not the only important aspect of this stage. If the force is loaded too fast, the energy is lost to early. The performance in tennis is based on the elastic energy. The usage of the elastic energy in tennis is based on the fact that the concentric action of the muscle will be higher if the motion begins from the point of muscles being under higher tension than if they were to contract just from a resting state.
For a muscle to begin the powerful motion, it must shorten first through the concentric contraction. So, if the muscle is lengthened (eccentric contraction) just prior to the contraction (not for long) , it will produce greater force using the stored elastic energy. For this to take place, the transition time between eccentric contraction and concentric contraction which is called amortization phase, should be very short. The stored elastic energy needs to be used rapidly, so the concentric contraction must follow the eccentric stretch before the energy disappears.
Rotation of the shoulders greater than the hips (bigger separation angle) during the take back phase in forehand, place oblique, abdominals and serratus anterior muscles on stretch. The separation angle creates the whip effect as during the unloading the hips decelerate but the shoulders accelerate as they uncoil and the shot is released. Therefore the full stretch of the abdominal oblique muscles, chest and shoulder muscles will prepare the upper body part of the player for the faster and more powerful muscle concentric contraction.

Unloading
As loading should be done in a slow manner, the unloading should be done in absolutely explosive manner. As the big muscles are loaded with the force the unloading of that force is directed from the big to small muscles which is pretty logical as we need bigger forces and the small muscles have very limited capacity. Powerful unloading is done in a slingshot manner. What does that mean? It means that that the loaded energy is transferred forwards as the body is rotating forward while the arm and wrist stayed behind. At that moment, influenced by the hip and torso forward rotation, the wrist and arm are at first moving shortly backwards but then with the further forward rotation of the hitting shoulder, the arm starts following (has to, no?) the forward rotation of the whole body. So the short backwards slowing down motion of the arm wrist followed by the forward acceleration through the ball creates this powerful slingshot motion. So going back to the loading- unloading part. The powerful slingshot motion does not exist without the hip and torso rotation, and this rotation is very weak and almost doesn’t exist if it’s not initiated from the toes and legs.
Unloading follows the proper loading and transfer of the stored energy through the kinetic chain. Unloading will not be efficient if the energy is stored for too long in the muscles as the player loses the momentum of unloading and transferring the energy to the ball. Muscles have limited capacity of storing the energy, so loaded player that waits for the ball will lose a lot of free potential energy that the ground is offering.

Finishing
All that tremendous energy that is directed to the ball while unloading has to be controlled as the tennis court is limited in size. Depending on the type of shot and the angle (racquet to the ball) at the impact, the follow through and finishing motion need to follow the initiated motion.
Follow through, no matter of the angle of the shot and amount of spin has to follow the direction of the ball. The body needs to complete the rotation forwards and trying to stop that motion in any unnatural and in untrained way will definitely result in an injury. As the arm is the last body part pulled forwards towards the contact point, following the impact point the player needs to make sure that the trajectory of the ball is followed by the arm and racquet. If you watch the players in slow motion, no matter of angles or body composition, the racquet and the arm are in the straight line right after the impact point. That happens before the elbow starts bending and directing the racquet towards the non hitting shoulder to complete the stroke.
Having the non dominant side of the body fully in control and stable enables the player to complete the follow through in the efficient way.
Having complete control over the biggest joints of the non hitting side will enable the player to transfer the energy forwards, through the ball and towards the target on the other side of the court. Stabilizing the shoulder and elbow and pulling them towards the non hitting hip, the player stabilizes the upper body during the follow through. In this way, the hitting side can rotate and reach forwards in an explosive way. At the time of the directing the racquet to the non dominant shoulder while finishing the shot, those same joints have to loose a bit so the upper body would rotate towards the non hitting shoulder (angular rotation of the upper body from the hip to the shoulder).
Stabilizing the front leg from the hip (stabilized by the elbow and shoulder with the help of the knee) to the knee and foot ankle, make sure that the most powerful transfer of the energy form the ground to the hitting hip is under control. Making sure that the front hip is stabilized is important for many reasons. First reason is that during the contact point, the hips should be aligned. Second reason is that without stabilizing the front hip, the amount of energy transferred from the legs to the upper body part is much less and not directed completely towards the ball. Third reason is that without the stable front hip (with the help of the knee and ankle joint), the defensive and wide shots can not be performed with control and power as the player wouldn’t be able to keep balance. No matter of stance that player chooses to play from, stabilizing the joints of the front leg is a priority for the efficient follow through as without it the player can still create great power but without control.
Depending on the type of stroke, the amount of spin, angle of the stroke or pronation and supination of the forearm the finishing is should be complete when the racquet is at the opposite side of the body. No matter of the type stroke, the racquet shouldn’t be finishing bellow the height of the elbow of the non hitting arm. Modern forehand strokes lately finish bellow the level of the shoulder, rarely over the shoulder as before was taught. The reason is the whip like motion of the strokes having the strokes more aggressive and the follow through trajectory is lower. Finishing with the racquet on the same side (hitting side) brings much more spin to forehand, but to perform this kind of stroke in an injury free manner, the player should be carefully physically prepared as it demands lots of forearm rotation.