1. Effects of Exercise on Biological Tissues Chapter 15 KINE 3301 Biomechanics of Human Movement

2. Structure of Bone Osteocytes in cortical bone are encased in lamellar layers. Several layers wrap around each other to form an osteon or Haversian system. The Haversian system in the center of the osteon contains blood vessels and nerve fibers. Volkmann’s canal forms interconnections between adjacent osteons.

3. Osteons in Cortical Bone From: Gardinier JD, et al. In situ permeability measurement of the mammalian lacunar-canalicular system. Bone, 46: 1075-1081. Used with permission from Elsevier.

4. Relation between Load and Structural Alignment Femoral image courtesy of Bartleby.com Inc. The alignment of cortical and cancellous bone tissue is arranged to withstand typical daily loads.

5. Stress – Strain for a Viscoelastic Material

6. From: Stolken JS, Kinney JH. On the importance of geometric nonlinearity in finite-element simulations of trabecular bone failure. Bone, 33: 494-504, 2003. Used with permission from Elsevier

7. Canaliculi Form Intercellular Communication Network From: Tanaka-Kamioka K, et al. In situ permeability measurement of the mammalian lacunar-canalicular system. J Bone Min Res, 13: 1555- 1568, 1988. Used with permission from Blackwell Science, Inc.

8. Stress – Strain for a Viscoelastic Material Osteocytes are embedded in osteons which are arranged around a central Haversian canal. Mechanical loading of bone generates fluid flow in the cannicular space, eliciting biochemical responses from the osteocytes to the imposed loads.

9. Material Testing System Images courtesy of Instron

10. Strain Units & Physiological Strain Microstrain (με) Units% Change in Length 1,000 microstrain1,000 με0.1% 10,000 microstrain10,000 με1.0% 25,000 microstrain25,000 με2.5% Physiological Strain Ranges for Long Bones 400 – 3,000 microstrain 400 – 3,000 με0.04 – 0.3% Seldom above 1,000 microstrain 1,000 με0.1%

11. Comparison of Stress – Strain for Cortical & Cancellous

12. Effects of Rate of Loading on Mechanical Response Viscoelastic tissues are stronger when loaded fast. The increased stiffness is attributed to the resistance of movement of fluid.

13. Relationship between Load and Fracture

15. Objective of Adaptive Bone Remodeling How does a region of bone cells determine the required strength for a region on bone? During walking peak strains are less than 1000 με. Strains in vigorous activities (landing, plyometrics) are 2000 – 3200 με (Fritton, 2000). The objective of adaptive remodeling is to maintain bone cell alignment and structural density so that typical daily loads produce strains of 400 – 1000 με.

16. Osteocytes Osteocytes are thought to inhibit osteoclasts from absorbing bone tissue. When a crack occurs the osteocyte network is no longer able to inhibit osteoclasts

17. What is the Advantage of Curved Bones? A curved bone deforms in a predictable direction. Increasing the magnitude of loading causes an increase in the osteogenic stimulus.

18. Measuring Bone Density with Dual-Energy X-Ray Absorptiometry (DEXA)

19. Example DEXA Measurement

20. Understanding DEXA Results 20 For BMD the DEXA reports T and Z Scores T Score: This number compares the amount of bone you have to a young adult of the same sex with peak bone mass. The T score is used to define osteoporosis: T −1 (T minus 1) or higher is normal T − 2.5 to -1 is considered osteopenia T − 2.5 and below is a diagnosis of osteoporosis The T score can be used to estimate fracture risk: T − 0 means your risk is the same as a normal 40 year old T − 1 means your risk is twice as likely T − 2 means your risk is four times as likely T − 3 means your risk is eight times as likely Z Score This number compares the amount of bone you have to a person in your age group of the same sex and size.

21. T-Score Compares BMD with a 40 Year Old 21

22. Trabecular Bone Thinning with Osteoporosis From Mosekilde L. Age-related changes in bone mass, structure, and strength – effects of loading. Z Rheumatol, 59 (Suppl 1):1-9, 2000. Used with permission from Steinkopff Verlag.

23. Articular Cartilage From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63

25. Impact Loading & Osteoarthritis From Radin EL, et al. Response of joints to impact loading – III. J Biomech, 6:51-57, 1973. Used with permission from Elsevier. The rabbit’s leg was impacted with a force of 1.5 BW that reached a peak in 50 ms. One hour of impacts were delivered each day. In 36 days: Cortical bone on the ends of the bone thickened, cancellous bone became brittle, cartilage was thin or non-existent.

26. 26 Radin’s Sheep Femoral condyle of sheep that walked on concrete Femoral condyle of sheep that walked on compliant wood chips Adult sheep were subjected to prolonged activity on hard surfaces by walking them daily on concrete and housing them on tarmac. Control sheep were walked on compliant wood chip surfaces and pastured. After 9 months the sheep exposed only to concrete walked with a limp. After 2 ½ years significant changes occurred: 1.Articular cartilage thinned or was non-existent. 2.Subchondral cortical bone thickened. 3.Trabecular pattern of cancellous bone was altered. 4.The increased cortical thickness and altered trabecular alignment stiffened the bone. Radin EL, Orr RB, Kelman JL, Igor LP, Rose RM. Effect of prolonged walking on concrete on the knees of sheep. J Biomech. 15:487-492, 1982.

27. Osteoarthritis

28. Knee Arthroscopy

29. Articular Cartilage From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63

30. Subchondral Bone Stiffening From: Herzog et al. The role of muscles in joint degeneration and osteoarthritis J Biomech, 40 S1: S54-S63 Cracks in articular cartilage are one of the first visible signs of the development of osteoarthritis. Radin & coworkers have suggested that subchondral bone stiffening may occur prior to any visible sign of the development of osteoarthritis.

31. Principles of Health Bone Loading for Physical Education Physical educators can optimize the osteogenic effect of exercise by incorporating exercises designed to stimulate healthy bone loading (McKay, et al. 2005). Physical educators should follow these principles to optimize healthy bone loading: 1.Children should perform 120 – 200 jumps / day, for 5 days/week. 2.Different types of jumps should be performed each day or each week. For example: week 1 – jumping rope, week 2 – hopping…., week 3 – shuttle run… 3.Static loads are not as effective as dynamic loads. 4.Spreading the activity over 3 – 5 days is far more effective than doing the jumping/hopping activity all in one day. Adapted from: McKay HA et al. “Bounce at the Bell”: a novel program of short bouts of exercise improves proximal femur bone mass in early pubertal children. Br J Sports Med, 39(8): 521 – 526, 2005.

32. Blood Vessels Invade Articular Cartilage

33. Yield Point for Ligaments & Tendons

34. Effects of Exercise on Ligaments & Tendons

35. Biomechanical Descriptors of the Mechanisms of Injury Minimum time for neuromuscular system to respond to a stimulus. Magnitude of force. Rate of force application. Point of force application. Direction of force application. Number of repetitions of loading. State of training (de-trained, immobilized, over- trained). Critical limits of the tissue (warm-up, previous injury). Magnitude of muscular preactivation.

36. Reflex Responses The minimum time of the neuromuscular system to respond to a stimulus is 80 – 200 ms. What happens when you go down a flight of stairs in the dark and you think you are at the bottom, but there is one more stair? This scenario illustrates the limitations of the neuromuscular system to respond to a stimulus.

37. Reflex Responses The minimum time of the neuromuscular system to respond to a stimulus is 80 – 200 ms. 30-120 ms from sensor (muscle spindle, GTO..) to initiation of muscle tension 50-300 ms for muscle to develop peak tension. Additional time will be necessary to overcome the momentum of the body:

38. 38 [Pope #226] The Role In Muscles In Preventing Injury Does strength training protect joints from injury? Yes, but it depends upon the rate of loading and the magnitude of preactivation of the muscles.

39. 39 Critical Limits of the Tissue The Antero-Talofibular Ligament can withstand approximately 139 N. [Nordin & Frankel, p 247 3Ed]

40. 40

41. 41 Prior to ground contact the knee extensors are pre- activated to prepare for the collision with the ground. Muscular Preactivation

42. EMG activity during landing from a drop height of 0.2 m with and without vision The rectified EMG recordings from the tibialis anterior, soleus, rectus femoris and biceps femoris muscles (TA, SO, RF and BF, respectively) during landings from a 0.2 m drop height are shown for ‘no vision’ and ‘vision’ conditions (left and right column, respectively). The traces are averages of five landings (subject 3). Dashed and continuous lines indicate take-off and touchdown, respectively. Calibration bars, expressed as a percentage of the EMG amplitude recorded during maximal voluntary contraction, apply to both landing conditions. From: Santello et al, Visual and non-visual control of landing movements in humans. J Physiol. 537 (Pt 1): 313-237, 2001.

43. Muscular Preactivation EMG activity during landing from a drop height of 0.8 m with and without vision Rectified EMG recordings from the TA, SO, RF and BF muscles during landings from a 0.8 m drop height are shown for ‘no vision’ and ‘vision’ conditions (left and right column, respectively). The traces are averages of five landings (subject 3). Dashed and continuous lines indicate take-off and touchdown, respectively. Calibration bars, expressed as a percentage of the EMG amplitude recorded during maximal voluntary contraction, apply to both landing conditions. From: Santello et al, Visual and non-visual control of landing movements in humans. J Physiol. 537 (Pt 1): 313-237, 2001.

44. Muscular Preactivaton From: Santello et al, The control of timing and amplitude of EMG activity in landing movements in humans. Exp Physiol. 83: 857-874, 1998. Soleus preactivation 100 ms prior to ground contact. Tibialis anterior preactivation 100 ms prior to ground contact.

45. Effects of Drop Height on Preactivation From: Santello et al., The control of timing and amplitude of EMG activity in landing movements in humans. Exp Physiol. 83: 857-874, 1998.

46. 46 Runner increases muscular preactivation with increasing running speed. Muscular Preactivation in Running

47. Direction & Point of Force Application

48. Magnitude of Force & Repetitions