Applications in Biomechanics

Goals of applied biomechanics: 1. Performance Improvement: focus on the different aspects of a technique and sport training 2. Injury Prevention and Rehabilitation: researched and developed by sports medicine specialists, trainers, and injured athletes

Continued…. 3. Fitness and Personal Training: biomechanical analysis can be applied to both exercise and exercise equipment

Overview…. Performance Improvement: Application 1 – The Pre-Stretch Application 2 – Training: Plyometrics Application 3 – Equipment Design Injury Prevention & Rehabilitation: Application 4 – Injury Risk Assessment Application 5 – Controlling Momentum Application 6 – Lifting an Object Fitness & Personal Training: Application 7 – Gaining Leverage Application 8 – Generating Tensile Force Application 9 – Evaluating Resistance Machines

PERFORMANCE IMPROVEMENT Application 1 – The Pre-Stretch (technique) For many skills (tennis serve, slap shot) the atlete's first action is in the opposite direction Wind-up or preparatory phase Is this a good thing or could it lead to an injury? This phase places the muscles into a stretch prior to using those muscle(s) for the desired action

PERFORMANCE IMPROVEMENT The tension or force generated is dependent on the muscle's ability to contract As the muscle is lengthened “passive” tension is also generated The connective tissue in the muscle offers resistance to the stretch which contributes to the stored elastic energy Think elastic recoil of a stretched rubber band

Performance Improvement The total tension of the muscle includes both active and passive components Therefore the pre-stretch preparatory phase can be very influential in the force output of a muscle If coaches and athletes can improve the pre-stretch, the action can be more effective (harder slap shot, tennis serve, etc)

TRAINING: PLYOMETRICS For an exercise to be plyometric, it must be a movement preceded by an eccentric (lengthening) contraction Eccentric lengthening performed before a rapid concentric contraction produces the greatest force and power capabilities

Training: Plyometrics The faster the muscle is lengthened, the greater the concentric force Therefore, training with pre-stretch prior to an explosive concentric contraction will allow for faster and more powerful change in direction

Equipment Design Example: golf Golf clubs have changed a lot over the years Materials used, length of the club's shaft, etc. Athletes must accommodate the changes in equipment in order to benefit from them

INJURY PREVENTION – INJURY RISK ASSESSMENT From a preventative and rehabilitative perspective, these principles should be followed: Resistance training should be progressive Warm-up should be tailored to the workout All key muscles must be stretched once warm Muscle imbalance needs to be addressed (are there muscles that are heavily used? They may be overly tight or their antagonist may be disproportionately weak)

INJURIES Injuries occur when the muscle is overloaded rapidly, during an eccentric contraction, when it is fatigued, or when used over a long duration Just as you can identify people at risk for heart disease, it is important to identify those who are at risk for muscle or tendon strain

Considerations Are the muscles recovered from previous workouts? Is there an existing injury that could be aggravated? Be aware of compensating for an injury Could make the athlete susceptible to another injury or muscle imbalance Is the athlete fatigued?

Controlling Momentum Muscles that are used to slow a movement are at risk for injury because they are contracted eccentrically The tension of the contraction may not be sufficient to withstand its attempt Example: the hamstrings slowing the hip flexion of a soccer or football kick

Lifting an Object The farther the mass is from the axis, the greater the moment of inertia and the greater the torque needed to cause rotation By positioning the object to be lifted closer to the body, less torque is required to perform the lift

FITNESS AND PERSONAL TRAINING Biomechanical analyses can give advice concerning: Positioning of joints to isolate specific muscles How to align the movement to the muscle How to combine muscles for optimal results Optimal speed Best starting position and range of motion for an exercise How to modify the leverage to gain a greater strength output

GAINING LEVERAGE You can use the lever systems to modify exercises to make them more challenging or to adjust the intensity As the resistance moves closer to the joint, the muscle will have an easier time moving it Moving the resistance further from the joint (fulcrum) increases difficulty

Generating Tensile Force Mechanics of muscle force generation are dependent on the velocity of shortening as well as muscle length The tension of a musculare contraction is the result of the attachment of crossbridges of the myosin to the actin filaments within the sarcomere Tensile force is proportional to the number of crossbridges ant the velocity of contraction Higher tension is developed at slower velocities of shortening

Evaluating Resistance Machines An examination of equipment should consider the following mechanical issues: Type of lever Axis of rotation Path and range of motion Machine resistance matching joint strength