European journal of applied physiology
-
Eur. J. Appl. Physiol. · Mar 2013
Aortic distensibility is reduced during intense lower body negative pressure and is related to low frequency power of systolic blood pressure.
As sympathetic activity approximately doubles during intense lower body negative pressure (LBNP) of -60 mmHg or greater, we examined the relationship between surrogate markers of sympathetic activation and central arterial distensibility during severe LBNP. Eight participants were exposed to progressive 8-min stages of LBNP of increasing intensity (-20, -40, -60, and -80 mmHg), while recording carotid-femoral pulse wave velocity (cPWV), stroke volume (SV), heart rate, and beat-by-beat blood pressure. The spectral power of low frequency oscillations in SBP (SBP(LF)) was used as a surrogate indicator of sympathetically modulated vasomotor modulation. ⋯ The mean correlation (r) between cPWV and SBP(LF) was 0.9 ± 0.03 (95 % CI 0.79-0.99). Severe LBNP increased central stiffness and reduced total arterial compliance. It appears that increased sympathetic vasomotor tone during LBNP is associated with reduced aortic distensibility in the absence of changes in MAP.
-
Eur. J. Appl. Physiol. · Feb 2013
Randomized Controlled TrialThe effects of simulated obstructive apnea and hypopnea on arrhythmic potential in healthy subjects.
Preliminary evidence supports an association between OSA and cardiac dysrhythmias. Negative intrathoracic pressure, as occurring during OSA, may provoke cardiac dysrhythmias. Thus, we aimed to study the acute effects of simulated apnea and hypopnea on arrhythmic potential and measures of cardiac repolarization [QT(C) and T (peak) to T (end) intervals [TpTec]) in humans. ⋯ There were no significant changes of the QT(C) and TpTec intervals during central end-expiratory apnea. These data indicate that simulated obstructive apnea and hypopnea are associated with an increase of premature beats and prolongation of QT(C) and TpTec intervals. Therefore, negative intrathoracic pressure changes may be a contributory mechanism for the association between OSA and cardiac dysrhythmias.
-
Eur. J. Appl. Physiol. · Feb 2013
Muscle gearing during isotonic and isokinetic movements in the ankle plantarflexors.
Muscle-tendon gearing is the ratio of the muscle-tendon unit velocity to the fascicle velocity and can be expressed as the product of the gearing within the muscle belly and the gearing due to tendon stretch. Previous studies have shown that gearing is variable and increases at higher velocities. Changes in the muscle activation levels and force development have been suggested to affect tendon gearing and thus muscle-tendon unit gearing. ⋯ The level of muscle-tendon unit gearing is largely determined by the belly gearing, but its variability is driven by changes in tendon gearing that in turn is a factor of the muscle activation and coordination. The belly thickness of the medial gastrocnemius decreased during contractions, but increased for the lateral gastrocnemius. It is likely that changes to the belly shape and 3-dimensional structure are important to the gearing of the muscle.
-
Eur. J. Appl. Physiol. · Jan 2013
Randomized Controlled TrialRegenerative responses in slow- and fast-twitch muscles following moderate contusion spinal cord injury and locomotor training.
The aim of this study was to use the rat moderate spinal cord contusion model to investigate the effects of incomplete spinal cord injury (SCI) on the muscle regeneration process, comparing regeneration of slow-twitch plantarflexor soleus muscle and fast-twitch dorsiflexor tibialis anterior (TA) muscle. Additionally, we wanted to examine the effect of a week of locomotor training following incomplete SCI on the muscle regeneration process in these muscles and also determine if a week of similar locomotor training is sufficient to initiate muscle regeneration in control, non-injured rats. Thirty-two, adult, female, Sprague-Dawley rats were chosen for the study. ⋯ No significant regenerative process was observed in the fast-twitch TA. Increased muscle regeneration in soleus is suggested by our findings of increased expression of (1) insulin-like growth factor-1, involved in the activation of satellite cells; (2) Pax7, a marker of satellite cell activation; (3) myogenin, a muscle regulatory protein; and (4) embryonic myosin, an indicator of new muscle fiber formation. Locomotor training in control, non-injured animals did not induce similar changes towards the regenerative process.
-
Although placebos have repeatedly been shown to increase physical performance and endurance, much less is known about the effect of their negative counterpart, nocebos. Here, we employ negative suggestions and a sham electrical stimulation as a nocebo conditioning procedure in healthy subjects performing a leg extension exercise to total exhaustion. Using two different protocols, we analyze the contribution of expectation alone or the combination of conditioning and expectation to the nocebo effect evaluated as the change of work performed and rate of perceived exertion. We find that it is possible to negatively modulate the physical performance in both cases, and we argue that this effect can effectively offset the outcome of training programs.