| Summary: | Bone strength plays an important role in reducing fracture risk. Osteoporosis is a condition as a result of low bone strength and is characterized by deterioration of bone tissue and loss of bone mass, leading to increased fracture risk (Osteoporosis Canada, 2009). Impact loading through exercise has been well established as an activity to maintain and improve bone health (Schwab & Klein, 2008), with high impact activities eliciting a larger response in bone adaptation over low impact activities (Daly, 2007; Guadalupe-Grau, Fuentes, Guerra & Calbet, 2009). The high impact loading of brick breaking within martial arts should be of sufficient magnitude to elicit bone adaptation. PURPOSE: The overall purpose of this study was to examine if the bones of the loaded arm among martial artists with brick breaking experience appear to have adapted to the high impact loading of brick breaking. In order to address this the specific objectives are (1) determine if brick breakers have a larger percent side-to-side difference over age and size matched controls in bone strength index (BSIc) at the 4% radius and 6% ulna, SSIp at the 65% ulna and 50% humerus, and grip strength. (2) Determine if the total number of lifetime brick breaks is correlated with percent side-to-side difference in strength strain index (SSIp), a measure of torsional strength, at the 50% humerus. (3) Confirm the load experienced during the brick break can be considered high impact (>4 X body weight). METHODS: Male brick breakers (N=13, mean age 31.1 (SD 10.5) yrs) and their age and size matched controls (N=13, mean age 31.7 (10.8) yrs) had measurements of SSIp on both arms mid-humeri using pQCT (Stratec XCT2000). Brick breaking history was obtained by questionnaire. SSIp between arms in both groups was assessed by dependant t-tests and percent side-to-side difference (bilateral asymmetry)
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between groups was assessed by independent t-test. Brick breaking force was assessed with 9 black belt participants performing a total of 13 brick break attempts by striking a standard stack of 8 patio blocks on a force platform. RESULTS: Dominant humerus SSIp was 7.7% (124 mm3, p<0.001) greater in brick breakers and 5.3% (96 mm3, p=0.023) greater in controls. Side-to-side differences did not differ between the groups (mean difference of 2.4%, p=0.333). Brick breaking history of total breaks was moderately correlated (r=0.73, p=0.002) with torsional bone strength side-to-side difference. Peak vertical forces ranged from 2075 N to 4496 N (mean: 2960 N). CONCLUSION: Brick breakers bone strength in the loaded arm seemed to have not adapted to high impact forces. However, the association between total number of breaks (impacts) and side-to-side strength difference suggests that a minimum number of loading sessions may be required before significant strength adaptation occurs. The forces experienced during a brick breaking strike approach forces that are considered high impact in lower body activities.
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