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Ross Armstrong, Christopher Michael Brogden and Matt Greig

.43 and 1.22 times more likely to sustain injuries than midrange scores. 12 In contrast, it has been suggested that performance can be enhanced by JH. 13 To potentially determine the relationship between JH and mechanical loading, a standardized exercise routine is required, and one potential protocol

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Wendy M. Kohrt

The osteogenic response to mechanical stress is blunted with aging. It has been postulated that this decline in responsiveness is related to (a) a limited ability to engender the strain necessary to reach the bone modeling threshold, due to decreased muscle mass and strength, and/or (b) a decline in certain hormones or growth factors that may interact with mechanical signals to change the sensitivity of bone cells to strain. There is reason to believe that both of these factors contribute to the reduced ability to increase bone mass through exercise with advancing age. Weight-bearing endurance exercise and resistance exercise have both been found to increase bone mass in older women and men. However, exercise training studies involving older individuals have generally resulted in increased bone mineral density only when the exercise is quite vigorous. There is also evidence that the osteogenic response to mechanical loading is enhanced by estrogens. Whether age-related changes in other factors (e.g., other hormones, growth factors, cytokines) also contribute to the reduced responsiveness of the aged skeleton to mechanical loading remains to be investigated.

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Ando Pehme, Karin Alev, Priit Kaasik and Teet Seene

The purpose of this study was to investigate the effect of compensatory hypertrophy (CH), heavy-resistance exercise training (HRET), and simultaneous CH and HRET on fast-twitch skeletal-muscle myofibrillar-protein synthesis, myosin heavy-chain (MHC) turnover rate, and MHC-isoform composition in young and old rats. In young animals all treatments intensified myofibrillar-protein synthesis, whereas in old animals with CH protein synthesis remained unchanged. The relative content of MHC I and IID in plantaris muscle increases with age, and the relative content of MHC IIB decreases. HRET and simultaneous CH and HRET decreased the proportion of MHC IIB and IIA and increased that of MHC IID in young rat muscle. In old rat muscle, relative content of MHC IID decreased and that of MHC IIB increased. CH decreased relative content of MHC IIB in both age groups and of MHC IIA in old animals. Relative content of MHC IID increased in both groups, and of MHC IIA, in young animals. MHC in plantaris of young rats turned over much faster in all types of mechanical loading but in old rats only during HRET and its combination with CH.

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Mathieu Lacome, Ben M. Simpson, Yannick Cholley and Martin Buchheit

high mechanical load (MechL; acceleration/deceleration/change of direction) at low speed than distance covered at HS. Therefore, the purpose of this study was to (1) compare the locomotor (HS running and external MechL) and heart rate (HR) responses between floaters and regular players during both

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Niels J. Nedergaard, Mark A. Robinson, Elena Eusterwiemann, Barry Drust, Paulo J. Lisboa and Jos Vanrenterghem

Purpose:

To investigate the relationship between whole-body accelerations and body-worn accelerometry during team-sport movements.

Methods:

Twenty male team-sport players performed forward running and anticipated 45° and 90° side-cuts at approach speeds of 2, 3, 4, and 5 m/s. Whole-body center-of-mass (CoM) accelerations were determined from ground-reaction forces collected from 1 foot–ground contact, and segmental accelerations were measured from a commercial GPS accelerometer unit on the upper trunk. Three higher-specification accelerometers were also positioned on the GPS unit, the dorsal aspect of the pelvis, and the shaft of the tibia. Associations between mechanical load variables (peak acceleration, loading rate, and impulse) calculated from both CoM accelerations and segmental accelerations were explored using regression analysis. In addition, 1-dimensional statistical parametric mapping (SPM) was used to explore the relationships between peak segmental accelerations and CoM-acceleration profiles during the whole foot–ground contact.

Results:

A weak relationship was observed for the investigated mechanical load variables regardless of accelerometer location and task (R 2 values across accelerometer locations and tasks: peak acceleration .08–.55, loading rate .27–.59, and impulse .02–.59). Segmental accelerations generally overestimated whole-body mechanical load. SPM analysis showed that peak segmental accelerations were mostly related to CoM accelerations during the first 40–50% of contact phase.

Conclusions:

While body-worn accelerometry correlates to whole-body loading in team-sport movements and can reveal useful estimates concerning loading, these correlations are not strong. Body-worn accelerometry should therefore be used with caution to monitor whole-body mechanical loading in the field.

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Susan A. Bloomfield

To define the cellular and molecular mechanisms for the osteogenic response of bone to increased loading, several key steps must be defined: sensing of the mechanical signal by cells in bone, transduction of the mechanical signal to a biochemical one, and transmission of that biochemical signal to effector cells. Osteocytes are likely to serve as sensors of loading, probably via interstitial fluid flow produced during loading. Evidence is presented for the role of integrins, the cell’s actin cytoskeleton, G proteins, and various intracellular signaling pathways in transducing that mechanical signal to a biochemical one. Nitric oxide, prostaglandins, and insulin-like growth factors all play important roles in these pathways. There is growing evidence for modulation of these mechanotransduction steps by endocrine factors, particularly parathyroid hormone and estrogen. The efficiency of this process is also impaired in the aged animal, yet what remains undefined is at what step mechanotransduction is affected.

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Ewald M. Hennig and David J. Sanderson

Foot function and possible mechanisms for the etiology of frequently observed forefoot complaints in bicycling were studied. Pedal forces and in-shoe pressure distributions were measured with 29 subjects, who rode on a stationary bicycle with a cadence of 80 rpm at 100, 200, 300, and 400 W. The influence of footwear on foot loading was also investigated by comparing running and bicycling shoes at 400 W. The first metatarsal head and the hallux were identified as the major force-contributing structures of the foot. High pressures under the toes, midfoot, and under the heel showed that all foot areas contribute substantially to the generation of pedal forces. For increasing power outputs, higher peak pressures and relative loads under the medial forefoot were identified. These may cause pressure-related forefoot complaints and accompany increased foot pronation. As compared to the running shoe, the stiff bicycling shoe demonstrated a more evenly distributed load across the whole foot and showed a significantly increased index of effectiveness.

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Belinda R. Beck

osteogenic response to mechanical loading. Indeed longitudinal data indicate that around 30% of adult female spine bone mineral is “accumulated in the 3 years around the onset of puberty” and that physical activity is associated with more rapid mineralization during puberty than before or after ( 77 ). A 6

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Adam Jones, Richard Page, Chris Brogden, Ben Langley and Matt Greig

climatic challenges, and reduced maintenance costs. However, each variation of playing surface will have specific characteristics and mechanical properties, 3 with implications for mechanical loading and subsequent risk of injury. 4 Reviews of the literature have typically reported no difference in

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Matt Greig, Hannah Emmerson and John McCreadie

Global Positioning System (GPS) technology offer potential to quantify mechanical loading during functional rehabilitative tasks. Recently, mediolateral loading imbalances were highlighted in a case study of ankle sprain injury in elite male soccer. 11 However, to enhance the clinical application of GPS