Enhanced Bone Size, Microarchitecture, and Strength in Female Runners with a History of Playing Multidirectional Sports.

PURPOSE: Female runners have high rates of bone stress injuries (BSIs), including stress reactions and fractures. The current study explored multidirectional sports (MDS) played when younger as a potential means of building stronger bones to reduce BSI risk in these athletes. METHODS: Female collegiate-level cross-country runners were recruited into groups: 1) RUN, history of training and/or competing in cross-country, recreational running/jogging, swimming, and/or cycling only, and 2) RUN + MDS, additional history of training and/or competing in soccer or basketball. High-resolution peripheral quantitative computed tomography was used to assess the distal tibia, common BSI sites (diaphysis of the tibia, fibula, and second metatarsal), and high-risk BSI sites (base of the second metatarsal, navicular, and proximal diaphysis of the fifth metatarsal). Scans of the radius were used as control sites. RESULTS: At the distal tibia, RUN + MDS ( n = 18) had enhanced cortical area (+17.1%) and thickness (+15.8%), and greater trabecular bone volume fraction (+14.6%) and thickness (+8.3%) compared with RUN ( n = 14; all P < 0.005). Failure load was 19.5% higher in RUN + MDS ( P < 0.001). The fibula diaphysis in RUN + MDS had an 11.6% greater total area and a 11.1% greater failure load (all P ≤ 0.03). At the second metatarsal diaphysis, total area in RUN + MDS was 10.4% larger with greater cortical area and thickness and 18.6% greater failure load (all P < 0.05). RUN + MDS had greater trabecular thickness at the base of the second metatarsal and navicular and greater cortical area and thickness at the proximal diaphysis of the fifth metatarsal (all P ≤ 0.02). No differences were observed at the tibial diaphysis or radius. CONCLUSIONS: These findings support recommendations that athletes delay specialization in running and play MDS when younger to build a more robust skeleton and potentially prevent BSIs.

Effect of sensory blockade and rate of sensory stimulation on local heating induced axon reflex response in facial skin.

Local neuronal circuits in non-glabrous skin drive the initial increase of the biphasic cutaneous vasodilation response to fast non-noxious heating. Voltage-sensitive Na+ (NaV) channel inhibition blocks the afferent limb of the non-glabrous forearm cutaneous axon reflex. Slow local heating does not engage this response. These mechanisms have not been adequately investigated or extended into areas associated with flushing pathology. We hypothesized that despite regional differences in sensory afferents, both sensory blockade and slowing the heating rate would abate the cutaneous axon reflex-mediated vasodilator responses in facial skin. We measured skin blood flow responses (laser-Doppler flowmetry) of 6 healthy subjects (5 female) to non-noxious forearm, cheek, and forehead local heating, expressed as a percentage of cutaneous vascular conductance at plateau (CVC = flux/mean arterial pressure). We assessed CVC during fast (1 °C/30s) and slow (1 °C/10 min) local heating to 43 °C in both NaV inhibition (topical 2.5% lidocaine/prilocaine) and control conditions. NaV inhibition decreased forearm (control: 84 ± 4, block: 34 ± 9%plateau, p < 0.001) and trended toward decreased forehead (control: 90 ± 3, block: 68 ± 3%plateau, p = 0.057) initial CVC peaks but did not alter cheek responses (control: 90 ± 3, block: 92 ± 13%plateau, p = 0.862) to fast heating. Slow heating eliminated the initial CVC peak incidence for all locations, and we observed similar results with combined slow heating and NaV inhibition. Slower sensory afferent activation rate eliminated the axon reflex response in facial and non-glabrous skin, but topical sensory blockade did not block axon reflex responses in flushing-prone cheek skin. Thus, slower heating protocols are needed to abate facial, particularly cheek, axon reflex responses.