The effect of intermittent running on biomarkers of bone turnover.

Intermittent exercise might be an efficient means of exercise for improving bone strength and quality. The aim of our study was to examine the effect of intermittent running on bone turnover markers using altered exercise-to-rest intervals. Twelve males completed one control (no exercise), and three, 45-min intermittent protocols (5, 20, and 80 s intervals) matched for distance and speed. Fasted venous blood samples were collected at baseline, 1, 2 and 24 h post-exercise. Carboxyterminal crosslinked telopeptide (CTX-I) and procollagen type 1 amino-terminal propeptide (P1NP) were used as markers of bone resorption and formation. After adjustment for baseline, CTX-I concentration at 1 h was higher (very likely to most likely small) for 5 s (30.2%; ±90% confidence limits: 10%), 20 s (2.9.0%; ±10%) and 80 s (32.0%; ±10%) compared to control. The very likely small effect remained for 5 s at 2 h (30.2%; ±15%). The effect for 20 and 80 s was possibly trivial and possibly small/possibly trivial (∼14.5%; ±âˆ¼15%). Differences in P1NP concentrations were likely to very likely trivial (∼7.4%; ±âˆ¼7.6%). Circulating CTX-I concentration is affected acutely by intermittent running with short-interval (5 s) intermittent loading resulting in a prolonged attenuation in circadian rhythm of CTX-I up to 2 h that was not demonstrated as clearly by longer intervals despite matched internal and external training load.

The mechanical loading and muscle activation of four common exercises used in osteoporosis prevention for early postmenopausal women.

High impact exercise can reduce postmenopausal bone loss, however stimulus frequency (loading cycles per second) can affect osteogenesis. We aimed to examine the effect of stimulus frequency on the mechanical loading of four common osteoporosis prevention exercises, measuring body acceleration and muscle activation with accelerometry and electromyography (EMG), respectively. Fourteen early postmenopausal women completed randomised countermovement jumps (CMJ), box-drops (BD), heel-drops (HD) and stamp (STP) exercises for continuous and intermittent stimulus frequencies. Sacrum accelerometry and surface electromyography (EMG) of four muscles were recorded. CMJ (mean ±â€¯SD: 10.7 ±â€¯4.8 g & 10.0 ±â€¯5.0 g), BD (9.6 ±â€¯4.1 g & 9.5 ±â€¯4.0 g) and HD (7.3 ±â€¯3.8 g & 8.6 ±â€¯4.4 g) conditions generated greater peak acceleration than STP (3.5 ±â€¯1.4 g & 3.6 ±â€¯1.7 g) across continuous and intermittent trials. CMJ and BD generated greater acceleration gradients than STP across continuous and intermittent trials. CMJ generated greater rectus femoris EMG than all other exercises, CMJ and BD generated greater semitendinosus and tibialis anterior EMG than HD across continuous and intermittent trials. CMJ and BD provide greater peak acceleration than STP and remain similar during different stimulus frequencies. CMJ, BD and HD may exceed STP in maintaining postmenopausal bone health.

Tibial impacts and muscle activation during walking, jogging and running when performed overground, and on motorised and non-motorised treadmills.

PURPOSE: To examine tibial acceleration and muscle activation during overground (OG), motorised treadmill (MT) and non-motorised treadmill conditions (NMT) when walking, jogging and running at matched velocities. METHODS: An accelerometer recorded acceleration at the mid-tibia and surface EMG electrodes recorded rectus femoris (RF), semitendinosus (ST), tibialis anterior (TA) and soleus (SL) muscle activation during OG, MT and NMT locomotion whilst walking, jogging and running. RESULTS: The NMT produced large reductions in tibial acceleration when compared with OG and MT conditions across walking, jogging and running conditions. RF EMG was small-moderately higher in the NMT condition when compared with the OG and MT conditions across walking, jogging and running conditions. ST EMG showed large and very large increases in the NMT when compared to OG and MT conditions during walking whilst SL EMG found large increases on the NMT when compared to OG and MT conditions during running. The NMT condition generated very large increases in step frequency when compared to OG and MT conditions during walking, with large and very large decreases during jogging and very large decreases during running. CONCLUSIONS: The NMT generates large reductions in tibial acceleration, moderate to very large increases in muscular activation and large to very large decreases in cycle time when compared to OG and MT locomotion. Whilst this may decrease the osteogenic potential of NMT locomotion, there may be uses for NMTs during rehabilitation for lower limb injuries.

The cardiovascular response to underwater pedaling at different intensities: a comparison of 4 different water stationary bikes.

AIM: Among the fitness activities, cycling in water immersion performed with water stationary bikes (WSB) has become very popular. However, there is a lack of information concerning their physiological demand. The aim of the present study was to assess the cardiovascular responses to four WSBs. METHODS: Twenty-two healthy participants underwent a graded exercise test on a cycle ergometer. Sixteen of them, 8 males (age 31.5 + or - 8.2 years) and 8 females (age 31.9 + or - 5.8 years) with the same level of peak oxygen consumption (VO(2peak)) were chosen and submitted, in random order, to four incremental testing sessions performed with four different models of WSB, one with no resistance (WSB1), two with resistance added to the bottom bracket axle (WSB2 and WSB3), one with resistance added to the pedals (WSB4). The VO(2peak) and heart rate peak (HR(peak)) were measured in all five conditions. RESULTS: Since no significant main effect for gender was detected, the data were grouped and analyzed all together. No significant differences were found in VO(2peak) and HR(peak) within the five testing conditions, whilst time to exhaustion (P<0.01) and pedaling frequency (RPM) at volitional exhaustion (P<0.01) were both significantly different across the four WSBs. When pedaling at 70 RPM, the oxygen consumption and heart rate response (as % of VO(2peak) and HR(peak)) were approximately 45% and 60% for WSB1, 60% and 70% for WSB3, 90% and 90% for WSB2 and WSB4, respectively. CONCLUSIONS: The present results provide useful information for instructors and practitioners because they demonstrate that different models of WSBs could elicit very different cardiovascular responses.

The assessment of path linearity in swimming: a pilot study.

The lateral-medial displacement (LF) and the overall drift from a straight path (DT) were quantified and compared in 5 top-level (TLS) and 5 low-level (LLS) crawl swimmers. Sixteen repetitions of 25-m crawl at increasing intensity were performed and videotaped. The performances were divided into 3 intensities (< 80 %, 80 - 90 % and > 90 % of maximal speed). LF was expressed as overlength swum (OLS) and coefficient of variation (CV) of the Z-component movement. OLS revealed a significant main effect for swimmer level (p < 0.01), intensity (p < 0.01) and their interaction (0.48, 0.37, 0.31-m for TLS and 0.47, 0.43, 0.44-m for LLS, p < 0.05). CV was significantly higher in LLS at the lowest (0.69 vs. 0.22, p < 0.05) and highest intensity (0.71 vs. 0.33, p < 0.05). DT, expressed as the slope of the linear regression of position data vs. time, was significantly higher in LLS only at the highest intensity (0.025 vs. 0.013, p < 0.05). The amount of dissipated energy due to LF, quantified by means of discrete Fourier analysis, revealed a difference only when the 0 - 5 Hz and 5 - 10 Hz spectral windows were analysed separately. While LF has a practical significance since it contributes to increase drag, DT is negligible at least for short-distance events.

Rabbit brain glucose-6-phosphate dehydrogenase: biochemical properties and inactivation by free radicals and 4-hydroxy-2-nonenal.

Glucose-6-phosphate dehydrogenase (G6PD) purified from rabbit brain is composed of two identical subunits of 56 kDa. The enzyme exhibits biphasic pH curve, linear Arrhenius plot and elevated susceptibility to inactivation by metal catalyzed oxidation and thiol binding reagents. 4-Hydroxy-2-nonenal (HNE) is able to inactivate the enzyme after only a few minutes of incubation. Since reactive oxygen species and G6PD-HNE adducts form easily in brain under conditions of oxidative stress, these findings have important implications in the loss of active G6PD molecules in vivo, a process which lowers the antioxidant protection and may be critical for neuron survival.