Exercise Biomechanics Reading Assignment

• Textbooks:– Kreighbaum pp 233-241, Chapter 8 (spinal exercises and resistive exercise

equipment) Hamill pp 202-207, 216-222 (conditioning, stresses, and injury potential of lower extremity)

• Journal article summaries by students– Nicholls et al (2002) Bat kinematics in baseball: Implications for ball extit

velocity and player safety. Journal of Applied Biomechanics, 19:283-294. – Hinterman and Nigg(1998) Pronation in runners: Implications for injuries.

Sports Medicine. 26:169-176.– O’Conner and Hamill (2002) Does running on a cambered road predispose

a runner to injury? Journal of Applied Biomechanics, 18:3-14.

Biomechanical correlates of exercise – areas of interest, endeavor, & contribution

• Design and analysis of fitness programs • Design of fitness exercises

– Which exercises are most effective in meeting program ogjectives?– Which exercises are potentially, or inherently unsafe and to be either avoided or

used with caution?– movements, forces, injury potential

• Analysis of fitness exercises– are exercises being executed properly?

• Design, selection, and analysis of fitness equipment– resistive equipment (e.g., thesis on abdominal ex equip)– aerobic equipment

• Relative merits of different exercise modes (e.g., stairclimber, bicycle, treadmill, rowing machine, elliptical exerciser)

• Running shoes

Methods of Evaluation of Ex Equip• Source: (Jung, A.P. The evaluation of home exercise equipment claims. ACSM’s

Health and Fitness Journal. 4(5): 14-16,30-31.• Check physiological and biomechanical principles and ACSM standards.• Review research, if available

– Critically review research – Are appropriate methods used? Who sponsored it? Where was research reported?

• Ask professors or other experts (Barstow, Harms, Gyurcsik, Estabrooks, Ferguson) • Review product reviews in fitness magazines (Club Industry, Athletic Business,

Fitness Management)• Try it yourself.• Interview professionals who have supervised its use.• Design and conduct your own research.• Note: guidelines for selection are on Federal Trade Commission Website (

http://www.ftc.gov)

Criteria for evaluating aerobic exercises• Degree of overload on cardiorespiratory system• Relevance to fundamental movements and activities of daily

living• Proportion of total body musculature involved• Degree of compressive stress on femoral head and lumbar

vertebral bodies (sites of most osteoporotic fractures)• Compressive stress on patella and knee joint• Range of motion and torque at hip, knee, and lumbar spine• Motivational features (comfort, user friendly, feedback, RPE)• Likelihood of continued usage• Cost• Other?

Biomechanical and anthropometric considerations in selecting and conducting

aerobic exercises• Potential for injury increases with body weight• Airborne activities produce greater forces than non-airborne activities• Fast twisting movements of arm and upper trunk produce lower back reaction forces• Stress is inversely proportional to body surface area exposed• Joint shear stress is minimal if bones are aligned in a straight line• Knee joint stress is minimized it knee is alighted above the foot• Alignment of trunk above pelvis minimizes unbalanced stress of spine• Keep limbs close to trunk for maximum equilibrium• Longer limbs involve greater MOI, thus they are harder to move and accelerate• Joint reaction force increases with speed of angular movement• The taller person needs more time to perform an activity• Safety can be increased or decreased by modifying the intensity of the exercise

Biomechanics of Resistive exercises

• Factors affecting force application– Force-velocity relationship

– Strength-joint position relationship (combination of angle of pull and force/length relationship)

• Should we provide the same degree of overload throughout the movement? If so, how do we do it?

Use of Cams in Ex Equipment:

Pelvic Girdle Balance

Lumbar spinal shear force is directly related to pelvic girdle position

Spinal Flexion Exercises

• Effect of– Anchoring feet?– Bending knees?– Placement of hands and

arms?– Inclined board?

Back Extension Exercises to Avoid:

Good morning exercise:Hyperextended back:

Recommended Extension Exercise

Effect of speed on effects of exercise:Torque = Wd + MOI x ang acc

Effect of posture on lumbar compression force:

Lifting quidelines: (1)bend knees (2)keep weight close to hips

Knee Joint Structure:

25% of Alpine skiing injuries are ligament injuries Peripatellar pain (runner’s knee) caused by imbalance of stress on patella

Lower Extremity Misalignment:

Q angle is larger in females due to Wider hip structure, increasing potential for PFPS (Patellofemoral pain syndrome)

Quadriceps Tendon and Patella Force LinesCompressive force at PFJ is ½ bodywt during normal walking, and over 3 times bw during stair climbingComp force increases as knee flexionAngle increases

Cruciate Ligaments and Shear Stress

Loads on Knee

• Forces at tibiofemoral Joint– Shear stress is greater during open kinetic chain exercises

such as knee extensions and knee flexions– Compressive stress is greater during closed kinetic chain

exercises such as squats and weight bearing exercises.

• Forces at Patellofemoral Joint– With a squat, reaction force is 7.6 times BW on this joint.

• Beneficial to rehab of cruciate ligament or patellofemoral surgery

Movement of subtalar joint

Foot Pronation and Tibial Torsion:

Rearfoot Movement During Running:

Types of running injuries

Example of Double Density Midsole:

Effects of Rear-foot Double Density Midsole on rearfoot position:

Effects of Rearfoot & Forefoot Double Density Midsole on takeoff angle: