David Paul Sumners

Montmorency Cherry Juice Reduces Muscle Damage Caused by Intensive Strength Exercise

PURPOSE Montmorency cherries contain high levels of polyphenolic compounds including flavonoids and anthocyanins possessing antioxidant and anti-inflammatory effects. We investigated whether the effects of intensive unilateral leg exercise on oxidative damage and muscle function were attenuated by consumption of a Montmorency cherry juice concentrate using a crossover experimental design. METHODS Ten well-trained male overnight-fasted athletes completed two trials of 10 sets of 10 single-leg knee extensions at 80% one-repetition maximum. Trials were separated by 2 wk, and alternate legs were used in each trial. Participants consumed each supplement (CherryActive® (CA) or isoenergetic fruit concentrate (FC)) for 7 d before and 48 h after exercise. Knee extension maximum voluntary contractions (MVC) were performed before, immediately after, and 24 and 48 h after the damaging exercise. Venous blood samples were collected at each time point, and serum was analyzed for creatine kinase (CK) activity, nitrotyrosine, high-sensitivity C-reactive protein, total antioxidant capacity, and protein carbonyls (PC). Two-way repeated-measures ANOVA were used for statistical analysis of the data. RESULTS MVC force recovery was significantly faster (24 h: CA 90.9% ± 4.2% of initial MVC vs FC 84.9% ± 3.4% of initial MVC; 48 h: CA 92.9% ± 3.3% of initial MVC vs FC 88.5% ± 2.9% of initial MVC (mean ± SEM); P < 0.05) after CA than FC consumption. Only serum CK and PC increased significantly from baseline, peaking 24 h after exercise (P < 0.001). The exercise-induced increase in CK activity was not different between trials. However, both the percentage (24 h after: CA 23.8% ± 2.9% vs FC 82.7% ± 11.7%; P = 0.013) and absolute (24 h after: CA 0.31 ± 0.03 nmol·mg(-1) protein vs FC 0.60 ± 0.08 nmol·mg(-1) protein; P = 0.079) increase in PC was lower in CA than FC trials. CONCLUSIONS Montmorency cherry juice consumption improved the recovery of isometric muscle strength after intensive exercise perhaps owing to the attenuation of the oxidative damage induced by the damaging exercise.

Repeated sprint training in normobaric hypoxia

Repeated sprint ability (RSA) is a critical success factor for intermittent sport performance. Repeated sprint training has been shown to improve RSA, we hypothesised that hypoxia would augment these training adaptations. Thirty male well-trained academy rugby union and rugby league players (18.4±1.5 years, 1.83±0.07 m, 88.1±8.9 kg) participated in this single-blind repeated sprint training study. Participants completed 12 sessions of repeated sprint training (10×6 s, 30 s recovery) over 4 weeks in either hypoxia (13% FiO2) or normoxia (21% FiO2). Pretraining and post-training, participants completed sports specific endurance and sprint field tests and a 10×6 s RSA test on a non-motorised treadmill while measuring speed, heart rate, capillary blood lactate, muscle and cerebral deoxygenation and respiratory measures. Yo-Yo Intermittent Recovery Level 1 test performance improved after RS training in both groups, but gains were significantly greater in the hypoxic (33±12%) than the normoxic group (14±10%, p<0.05). During the 10×6 s RS test there was a tendency for greater increases in oxygen consumption in the hypoxic group (hypoxic 6.9±9%, normoxic (−0.3±8.8%, p=0.06) and reductions in cerebral deoxygenation (% changes for both groups, p=0.09) after hypoxic than normoxic training. Twelve RS training sessions in hypoxia resulted in twofold greater improvements in capacity to perform repeated aerobic high intensity workout than an equivalent normoxic training. Performance gains are evident in the short term (4 weeks), a period similar to a preseason training block.

Experimental Evidence of the Tonic Vibration Reflex during Whole-Body Vibration of the Loaded and Unloaded Leg

Increased muscle activation during whole-body vibration (WBV) is mainly ascribed to a complex spinal and supraspinal neurophysiological mechanism termed the tonic vibration reflex (TVR). However, TVR has not been experimentally demonstrated during low-frequency WBV, therefore this investigation aimed to determine the expression of TVR during WBV. Whilst seated, eight healthy males were exposed to either vertical WBV applied to the leg via the plantar-surface of the foot, or Achilles tendon vibration (ATV) at 25Hz and 50Hzfor 70s. Ankle plantar-flexion force, tri-axial accelerations at the shank and vibration source, and surface EMG activity of m. soleus (SOL) and m. tibialis anterior (TA) were recorded from the unloaded and passively loaded leg to simulate body mass supported during standing. Plantar flexion force was similarly augmented by WBV and ATV and increased over time in a load- and frequency dependent fashion. SOL and TA EMG amplitudes increased over time in all conditions independently of vibration mode. 50Hz WBV and ATV resulted in greater muscle activation than 25Hz in SOL when the shank was loaded and in TA when the shank was unloaded despite the greater transmission of vertical acceleration from source to shank with 25Hz and WBV, especially during loading. Low-amplitude WBV of the unloaded and passively loaded leg produced slow tonic muscle contraction and plantar-flexion force increase of similar magnitudes to those induced by Achilles tendon vibration at the same frequencies. This study provides the first experimental evidence supporting the TVR as a plausible mechanism underlying the neuromuscular response to whole-body vibration.

Wide-Pulse Electrical Stimulation to an Intrinsic Foot Muscle Induces Acute Functional Changes in Forefoot–Rearfoot Coupling Behaviour during Walking

Interventions for strengthening intrinsic foot muscles may be beneficial for rehabilitation from overuse injuries. In this study the acute effects of high-frequency, low-intensity wide-pulse electrical stimulation (WPS) over an intrinsic muscle on subsequent foot function during walking was assessed in healthy participants. WPS was delivered to the m. abductor hallucis (m.AH) of the non-dominant foot during relaxed standing. 3-dimensional forefoot (FF)--rearfoot (RF) coordination was quantified with a vector coding technique within separate periods of the stance phase to study WPS functional effects on foot motion. 4 types of coordinative strategies between the FF and RF were interpreted and compared PRE-to-POST-WPS for both the experimental and control feet. Bilateral electromyography (EMG) from m.AH was analysed during the intervention period for evidence of acute neuromuscular adaptation. The results showed that WPS significantly modulated FF-RF coordination during mid-stance, indicative of a more stable foot. Specifically, a statistically significant increase in FF eversion with concomitant RF inversion in the frontal plane and RF-dominated adduction in the transverse plane was observed. Subject-specific increases in post-stimulus m.AH EMG activation were observed but this was not reflected in an overall group effect. It is concluded that the structural integrity of the foot during walking is enhanced following an acute session of WPS and that this mechanical effect is most likely due to stimulation induced post-tetanic potentiation of synaptic transmission.

Increases in inspiratory neural drive in response to rapid oscillating airflow braking forces (vibration).

OBJECTIVE To investigate whether 10 breaths against a vibration stimulus elicits increments of spontaneous and maximal inspiratory mouth pressure (maxMP) and tidal mean inspiratory flow (iV(T)/T(I)) upon stimulus removal. METHODS Twelve healthy subjects (8 female, 4 male; 22-50 years old), recruited from the University student body, completed 3 maximal inspirations before (pre) and after (post) 10 inspirations against resistive loading with a vibration-type stimulus (VIB; youbreathe, Exoscience Ltd., London, UK), pressure-matched resistive loading (RES) or resting breathing (CON; no load). The trials were presented in a random order. maxMP and involuntary tidal breathing were compared pre and post conditioning. RESULTS Inspiratory neural drive increased only after VIB as evidenced by increased tidal and maxMP and mean inspiratory flow (iV(T)/T(I); p < 0.05). There was no effect of either resistance or control breathing on maximal maxMP or tidal responses. CONCLUSIONS Ten conditioning breaths of VIB lead to increased maximal inspiratory mouth pressure and spontaneous mouth pressure and mean inspiratory flow possibly through a common mechanism of increased descending respiratory drive.

Inspiratory high frequency airway oscillation attenuates resistive loaded dyspnea and modulates respiratory function in young healthy individuals

Direct chest-wall percussion can reduce breathlessness in Chronic Obstructive Pulmonary Disease and respiratory function may be improved, in health and disease, by respiratory muscle training (RMT). We tested whether high-frequency airway oscillation (HFAO), a novel form of airflow oscillation generation can modulate induced dyspnoea and respiratory strength and/or patterns following 5 weeks of HFAO training (n = 20) compared to a SHAM-RMT (conventional flow-resistive RMT) device (n = 15) in healthy volunteers (13 males; aged 20–36 yrs). HFAO causes oscillations with peak-to-peak amplitude of 1 cm H2O, whereas the SHAM-RMT device was identical but created no pressure oscillation. Respiratory function, dyspnoea and ventilation during 3 minutes of spontaneous resting ventilation, 1 minute of maximal voluntary hyperventilation and 1 minute breathing against a moderate inspiratory resistance, were compared PRE and POST 5-weeks of training (2×30 breaths at 70% peak flow, 5 days a week). Training significantly reduced NRS dyspnoea scores during resistive loaded ventilation, both in the HFAO (p = 0.003) and SHAM-RMT (p = 0.005) groups. Maximum inspiratory static pressure (cm H2O) was significantly increased by HFAO training (vs. PRE; p<0.001). Maximum inspiratory dynamic pressure was increased by training in both the HFAO (vs. PRE; p<0.001) and SHAM-RMT (vs. PRE; p = 0.021) groups. Peak inspiratory flow rate (L.s−1) achieved during the maximum inspiratory dynamic pressure manoeuvre increased significantly POST (vs. PRE; p = 0.001) in the HFAO group only. HFAO reduced inspiratory resistive loading–induced dyspnoea and augments static and dynamic maximal respiratory manoeuvre performance in excess of flow-resistive IMT (SHAM-RMT) in healthy individuals without the respiratory discomfort associated with RMT.