EXERCISE BIOMECHANICS Biomechanics All-encompassing term joining human anatomy and physiology with movement physics and mathematics to identify the effect of forces on the body Forces are constantly acting on the body; manipulating these forces allows for voluntary movement or maintenance of static positions (posture) Force = Mass x Acceleration These forces can be broken down into internal forces and external forces Internal Forces Forces acting within the body The two types of internal forces are: Tensile Forces: stretching forces, pulling at both ends of a structure along its length (skeletal muscle) Compressive Forces: pushing forces whose direction and point of application would tend to shorten or squeeze an object along the dimension coinciding with the line of action (smooth muscle) The body’s center of mass will stay the same unless external forces act upon it Picture yourself in outer space, contracting your muscles but going nowhere External Forces Forces acting upon the body: ✦ Gravity – non-contact, constant force pulling our body towards the earth’s surface ✦Contact Forces – force between two objects (or an object and a surface) that are in contact with each other; these objects can include wind, water, ground, etc. ✦ ✦ Normal Contact Force – forces acting equally and opposite (pushing down against the ground) Gravity Internal Forces create vertical and horizontal propulsion Frictional Force – forces running parallel to the two surfaces of the objects (between shoe surface and the ground) Normal Contact (Ground) Frictional Contact Balance Static Equilibrium is achieved when all torques and external forces acting on a body are equal Action and Reaction Forces In order to move a given load, the body must contribute an external force beyond the quantity of the resistance During the chest press, the pectoralis major and the force it creates is called the prime mover force Action and Reaction Forces In order to prevent any undesirable actions while exerting forces to accelerate a load, stabilize and neutralizer forces are used The more complex we make the chest press, the greater the need for stabilizer and neutralizer forces; reducing stability usually requires lowering the load Motion When the body is in motion, movements are quantified using space and time Linear motion (translocation) + angular motion (rotary motion) = general motion If the starting position is known motion can be broken down by: ✦ Speed – the time rate of change in position of a body without regard to ✦ ✦ direction Velocity – rate of motion or performance with regard to direction Acceleration – the rate of change in velocity Momentum Linear Momentum = Mass x Linear Velocity If a 20-lb MB is thrown to a 150-lb person at 10 mph, the force needed to stop the MB would be substantially more than the 20-lb weight of the ball To stop the ball the person would need to use internal forces (via muscle contractions) and external forces (ground reaction force and friction) to brace the impact Work Work = Force x Distance Positive Work = when the distance moved is in the direction of the force (e.g., a bar is pressed overhead); muscle contractions are considered concentric Negative Work = when the distance moved is opposite to the direction of the force (e.g., a bar is lowered); muscle contractions are considered eccentric Both negative and positive work contribute to improvements in strength Work • Step-up = positive work (concentric) • Step-down = negative work (eccentric) • Holding dumbbells = no work (isometric) Mechanical Energy Energy = capacity to perform work; mechanical energy takes two forms: Kinetic Energy = energy possessed by a body because of its motion Example: a wrecking ball swung from a crane into a building Potential Energy = energy stored in an object by virtue of its position Example: a weight held off of a top of a building As kinetic energy increases, potential energy proportionally decreases The further a rubber band is stretched, the greater the increase in potential energy When the band shortens, potential energy decreases as it is converted to kinetic energy Stretch-Shortening Cycle • • • • SSC uses potential energy converted into kinetic energy Eccentric to concentric overlap creates a gain in energy Example: easier to start in an eccentric position (RDL vs deadlift) Counter movements or rebounding increase energy potential Power Work can be accomplished in any variable of time; power is used to describe the amount of actual work performed in a given amount of time Power = Work/Time which is often converted into: Power = Force x Velocity Force-Velocity Curve Power activities are based on time of tension Power Velocity of Shortening Maximal power output among humans occurs between 30-60% (depending of the joint) Force Torque In the body, greater torque applied = greater internal forces needed to manage eccentric forces ➢ During an abdominal curl-up, more torque is applied when a weight is held overhead (far from the COM) rather than at chest level ➢ Distance between the fulcrum and point of resistance = resistance arm ➢ Longer resistance arm = greater necessary torque and difficulty managing the movement ➢ Consider the differing loads for a shoulder press and side raise exercise Implications of Torque The amount of force a muscle must overcome depends on the load and the length of the resistance arm The heavier the resistance, or the longer the resistance arm, the more difficult it is for the body to move the resistance Force Coupling Force couples create greater amounts of torque by applying opposing forces about an axis Our body uses the strategy of force coupling in order to increase force production The biceps brachii and brachioradialis both cross the elbow pulling from a different location Resistance Arm Line of Pull Torques created by the body are dependent upon the amount of force created by the muscle and its location; this is called the line of pull To reduce the risk for joint injury, the line of pull (often in the direction of the muscle tendon) should be in direct opposition to the line of resistance Manipulating Resistance Force Exercise difficulty can be manipulated by adjusting factors that contribute to resistive torques or by modifying the mechanical advantage of the lever system Increasing Difficulty • Lengthen the resistance arm • Increase the resistance • Shorten the force arm Decreasing Difficulty • Shorten the resistance arm • Decrease the resistance • Lengthen the force arm Most movement errors or “cheating” occurs to decrease difficulty Examples of Biomechanical Cheating • Hip extension during an incline press • Flexed arms during a side raise • Shoulder flexion during a bicep curl • Flexed hip during machine leg curls Stability Gravity is constantly pulling each object’s COM towards the earth; this position is referred to as the center of gravity (COG) At this point, weight is evenly distributed and balanced Our COG is typically centrally located from side to side, where we are symmetrical We are not symmetrical from front to back or top to bottom Fat patterns, posture, and muscle mass will dictate the precise position of the COG Center of Gravity and Stability We can shift the COG in all directions by moving our joints and/or holding a load The Kinetic Chain The ability of the body to stabilize its segments ultimately determines its performance External force energy must be transferred through the body’s kinetic chain to effectively join with internal forces If energy leaks out of unstable segments in the chain, the application of internal forces will be diminished A person completing the military press may not be able to reach full potential because part of the ground reaction force is lost due to instability in the trunk (energy leakage) Chains and Circuits Open Chain The distal extremity is free in space and not fixed or in contact with the ground Examples: machine-based and seated exercises Closed Chain Distal extremity is in contact with the ground or a fixed object Examples: push-ups, pull-ups, squats, deadlift Open Circuit Movements where the distal extremities do not act upon the same object Example: dumbbell press Closed Chain Movements where the distal extremities act upon the same object Example: barbell press Chains and Circuits Open Chain Closed Circuit Closed Chain Open Circuit Closed Chain Closed Circuit Open Chain Open Circuit Components of Stability Stability depends on the following variables: Mass of the object Height of the COG Line of gravitational pull Base of support Constant Manipulated by the body By managing these variables effectively, less internal and external force is required for stability Height of Center of Mass The lower the center of mass, the greater the stability More Stable Less Stable Line of Gravitational Pull The more central the line of gravity within the base of support, the greater the stability More Stable Less Stable Base of Support The wider the base of support in relation to the external force, the greater the stability More Stable Less Stable Dynamic Stability – Locomotion During locomotive activities (walking or running) the body moves by constantly losing and regaining stability; as we step, the line of gravity moves outside the base of support, essentially causing us to fall forward (under control) Tripping: If the swing leg fails to re-establish a base of support outside of the line of gravity, stability is lost and the runner falls Older adults often lose confidence in their ability to regain stability and take shorter, sideto-side steps in order to maintain the greatest stability Anaerobic Training Neuromuscular coordination * Studies have shown that strength, balance, agility, and jump training prevent functional decline Muscle hypertrophy Potential Benefits * Helps prevent the onset sarcopenia(muscle loss) Increased power and Increased force production Enhanced movement confidence *reducing falls in elders Improved Movement Economy and Sports performance *technique, reduced rate of fatigue, greater power output Improved range of motion * Helps with posture Improves body composition *Has been shown enhance lean mass( increases RMR ) Continued Metabolic enhancements *EPOC( *Improved insulin sensitivity Increased bone density *reducing risk of osteopenia and osteoporosis(BMD) Improved quality of life and function Training for a Desired Outcome Power : *Work must be performed rapidly, usually for relatively short periods of time *High-velocity contractions are employed (ballistic and plyometrics) *Relies heavily on the phosphagen energy system * limited mass gains Hypertrophy: *Training for increase muscle fiber size requires high time under tension while maintaining moderately –high force output in isolated muscle groups *Longer periods of muscular work forces reliance on glycolytic energy pathway *Relatively slow application of force promotes greater fiber recruitment *notable mass gains Training for a Desired Outcome Muscular Endurance: *Higher repetition ranges at lower force outputs *Muscle tissue is forced to become more efficient in the tolerance and removal of hydrogen, and at sustaining contractile force for longer periods of time before fatiguing * helps allows develop baseline muscular fitness and motor patterns * limited mass gains Strength * low to moderate volume , * moderate frequency & high intensity *limited mass gains *compound movements Health Goal Training Systems Priority Systems – performing exercises or activities that represent remedies to the greatest health risks – focus on deficiencies Circuit training systems- utilizes multiple exercises in a string with transitional rest in between sets. – combines benefits of fitness Strength Pyramid system- emphasizes an inverse relationship between weight and repetitions. – neural preparation for heavier loads Complex system- emphasize muscle recruitment and motor patterns – exercise emphasis is placed on a particular muscle group or joint. Negative set – overload the tissue neural demands – exercise is performed with more weight than can be lifted concentrically(eccentric movent) Training Systems Hypertrophy Superset – Two or more exercises sequenced together without rest(commonly agonist/ antagonist) – increase volume of work Drop set – same exercised used without rest between sets while resistance is reduced each new set. – maximizes muscle fiber recruitment Performance Contrast system- a heavy slow speed lift followed by a rapid light lift(plyometric); use same movement. – maximize force at different velocities Lactate tolerance system- Group o exercises performed as quickly as possible until all reps are completed. – maximize glycolytic pathway efficiency. Hypertrophy Volume: 30-40 sets, 3-5 sets per exercise, 8-12 repetitions Intensity: 70-85% 1RM Rest interval: 30-60 seconds (up to 90 sec) Frequency: 4-6x/week Mode/Emphasis: Muscle fiber recruitment, muscle isolation Training system: Supersets, drop sets, pyramid sets Endocrine response: Human growth hormone, testosterone, other anabolic and stressrelated agents Continued…. • Used to increase muscle mass; when abiding by training guidelines, applied stress promotes anabolic activity, assuming adequate energy and recovery is provided • The low blood pH seen with minimal rest is a catalyst for anabolic activity, but many lifters rest too long to provide the optimal stress (use a stopwatch) • Exercises that use larger muscle groups induce a greater hormonal response, benefiting all other muscles • For women concerned that hypertrophy training will make them “bulky” or appear masculine, provide education and modify programming as necessary • Females have much lower levels of testosterone when compared to males, making anabolic effects much harder to attain • Adding 1-2 pounds of muscle with an equal loss of fat will actually make the person look smaller without a change in BW • Slightly higher repetition ranges and lower intensities can be employed Strength Volume: 18-30 sets, 3-5 sets per exercise, 3-5 (nervous) 610(muscle) Intensity: 75-95% 1RM(phosphagen/glycolytic) Rest interval: 2-5 minutes- phosphagen 60-90 seconds glycolytic Frequency: 3-5x/week Mode/ Emphasis: Neural efficiency, compound lifts(cross joint lifts) Training system: Pyramid sets, negative sets Endocrine response: Testosterone, other anabolic and stress agents Continued…. • Strength – the ability to produce maximal force; movements that challenge the maximal capabilities of muscle will yield the greatest adaptations • Maximal force demands rapidly drain the phosphagen system, limiting exercise duration • Primarily associated with nervous system improvements rather than mass gains • Closed-chain, cross-joint lifts commonly employed increase the capabilities of stabilizing musculature (e.g., trunk, rotator cuff, scapular stabilizers) • Inexperienced lifters should initially focus on movement proficiency at relatively lower loads; using too much weight early on can lead to poor biomechanical compensations Anerobic Power Volume: Intensity: 30-50% 1RM(glycolytic) or 60-90% 1RM (CP) Rest interval: 30 sec – 4 minutes Frequency: 2-4x/week Recovery: 2-4 rest days per week Mode/Emphasis: speed development, hip extension and flexion, Olympic lifts, weighted ballistics Training system: Plyometrics, contrast Endocrine response: GH, testosterone, epinephrine Continued…. • Exercises employed use momentum and reflex actions to quickly generate significant force • Places high stress on muscle and connective tissues, largely due to necessary deceleration forces • Two distinct categories Heavy low rate power – performed at near –maximal or maximal velocity – causes rapid fatigue Light high rate power(glycolytic) –very high velocities with lower loads – onset of fatigue is much slower due to lower force/power output • Power training can be adapted for all populations by: o Manipulating the velocity or intensity employed o Focusing on the concentric phase by assisting or negating the eccentric component of the movement o Varying the complexity of movements performed • Example for older adults – rapid chair sit-to-stands Anerobic Endurance Volume: 30-45 sets/day /12-25 reps Intensity: 50-70% 1RM (glycolytic) Rest interval: 30-45 seconds Frequency: 3-5x/week Recovery: 2-4 rest days per week Mode/Emphasis: multiple modality/lactic acid system Training system: circuits/supersets Endocrine response: minimal GH, testosterone, epinephrine Fiber Recruitment Considerations Heavy Loads High Velocity Recruit fast and slow twitch fibers * Strength recruits high fast twitch fibers *Po wer Low velocity low weight recruits slow twitch fibers * Endurance Fiber Type Con siderations Type II X 50 grams of force Per motor unit 5 minute fatigue rate Typ e II A 30 grams of force per motor Unit 6 minute fatigue rate Type I 5 grams of force per motor unit fatigue resistant Endurance training Moderate to low intensity ha limited effect High intensity increases GH Hormone Interaction and Exercise Strength Training Increased Testosterone Moderate increase in GH Body building Increased Testosterone Increased GH – modulates IGF-1 Increased Cortisol Increased IGF Fast speed before Controlled Speed Complexity before Simple High Intensity before Low Intensity Order of Operations Large Muscles before small Muscle Cross joint Movements before single joint movements Multi- planar before Isolated Movements Asymmetrical before symmetrical Dynamic before Static New challenge to the body’s system should be applied once the task or challenge has been consistently met 2-5% increases in difficulty are well tolerated Generally a stimulus should be applied with some level of consistency for 3 weeks for neural patterning Progressions can come from a wide variety of stress beyond simply increasing resistance Progressions Movement Progressions Easy/Simple Bodyweight Movement Forward lunge Resisted Movement Forward Lunge w/Resistance Bodyweight + Mild Instability Forward lunge w/Lateral Reach Added Resistance + Mild Instability Movement Complexity Forward Lunge w/Reach holding Forward Lunge w/Asymmetrical medicine ball Reach to Reverse Lunge Hard /Complex Many factors affect the actual and perceived exertion including: *Resistance used *Speed of movement Exercise Intensity *Rest interval *Work interval *Balance and coordination requirements *Volume of work Resistance lifted correlates closely with repetitions performed. The appropriate resistance for each lift should be premediated from testing. Identifying Proper Intensity 2 repetitions = 95% 1RM 3 rep = 92.5% 4 reps = 90% 5 reps = 87.5% 6 reps = 85% 7 reps = 82.5% 8 reps = 80% 10 reps = 77.5% 11 reps = 75% 12 reps = 70% Effect of Age Decline in strength occurs with advancing age. With most significant rate of decline occurring after the 5th and 7th decade The primary loss is due to reduced fiber protein particularly in Type II Fibers, consequently affecting power output and mass. Elderly populations can make significant gains in strength throughout the later life with resistance training. Strength and power training are extremely important in the maintenance of independence Gender Differences Males experience a nearly 50% greater capacity for force production I the upper body musculature In absolute terms men are also stronger in the lower body by 25-30% Relative to lean mass women are comparable to male in strength Primary difference between genders is quantity of lean body mass Anaerobic programming for males and females is consistent Detraining Peak power declines roughly 10% in the first 3 weeks of training cessation Primary reasons for loss are reduction in lean mass, efficiency changes in the muscle fiber particularly enzymatic, and neuromuscular efficiency. Significant decline occurs after 12 weeks of detraining When volume decrease intensity should increase proportionately to compensate for the decline
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