Consequences of prolonged total thermoneutral immersion on muscle performance and EMG activity

Temporal adaptation of the postural control following a prolonged fin swimming

PURPOSE

Postural control deteriorates following a transition between two environments, highlighting a sensory conflict when returning to natural conditions. Aquatic immersion offers new perspectives for studying postural control adaptation in transitional situations. Our aim is to study immediate and post-task static postural control adaptation on land after a prolonged fin swimming exercise in total immersion.

METHODS

Standing static postural control was assessed in 14 professional or recreational SCUBA divers (11 men, 3 women; 33.21 ± 10.70 years), with eyes open and closed, before, immediately after, and in the following 20 min following a fully-immersed 45-min fin swimming exercise. Centre-of-pressure metrics (COP) including average position, amplitude, velocity, length and 95% ellipse were evaluated in medial-lateral (x-axis) and anterior-posterior (y-axis) directions with a force platform. The Romberg ratio was also assessed for each metric.

RESULTS

A two-way repeated measures analysis of variance revealed a significant effect of the measurement period on COPx vel (p = 0.01), COPy vel (p < 0.01) and Length (p < 0.01), and of the visual condition on COPy vel (p < 0.01) and Length (p < 0.01). Eyes closed measures were systematically higher than eyes open measures despite there being no significant difference in the Romberg ratio in all periods. Post-immersion, the velocity and total trajectory of the centre of pressure remained systematically lower than baseline values in both visual conditions.

CONCLUSION

Post-immersion, COP velocity and length significantly decreased, suggesting a sensory reweighting strategy potentially associated with ankle stiffening.

Impact of a Cold Environment on the Performance of Professional Cyclists: A Pilot Study

The practice of physical activity in a variable climate during the same competition is becoming more and more common due to climate change and increasingly frequent climate disturbances. The main aim of this pilot study was to understand the impact of cold ambient temperature on performance factors during a professional cycling race. Six professional athletes (age = 27 ± 2.7 years; height = 180.86 ± 5.81 cm; weight = 74.09 ± 9.11 kg; % fat mass = 8.01 ± 2.47%; maximum aerobic power (MAP) = 473 ± 26.28 W, undertook ~20 h training each week at the time of the study) participated in the Tour de la Provence under cold environmental conditions (the ambient temperature was 15.6 ± 1.4 °C with a relative humidity of 41 ± 8.5% and the normalized ambient temperature (T_awc) was 7.77 ± 2.04 °C). Body core temperature (T_co) was measured with an ingestible capsule. Heart rate (HR), power, speed, cadence and the elevation gradient were read from the cyclists’ onboard performance monitors. The interaction (multivariate analysis of variance) of the T_awc and the elevation gradient has a significant impact (F(1.5) = 32.2; p < 0.001) on the variables (cadence, power, velocity, core temperature, heart rate) and on each individual. Thus, this pilot study shows that in cold environmental conditions, the athlete’s performance was limited by weather parameters (ambient temperature associated with air velocity) and race characteristics. The interaction of T_awc and elevation gradient significantly influences thermal (T_co), physiological (HR) and performance (power, speed and cadence) factors. Therefore, it is advisable to develop warm-up, hydration and clothing strategies for competitive cycling under cold ambient conditions and to acclimatize to the cold by training in the same conditions to those that may be encountered in competition.

Effect of decompression-induced bubble formation on highly trained divers microvascular function

We previously showed microvascular alteration of both endothelium-dependent and -independent reactivity after a single SCUBA dive. We aimed to study mechanisms involved in this postdive vascular dysfunction. Ten divers each completed three protocols: (1) a SCUBA dive at 400 kPa for 30 min; (2) a 41-min duration of seawater surface head immersed finning exercise to determine the effect of immersion and moderate physical activity; and (3) a simulated 41-min dive breathing 100% oxygen (hyperbaric oxygen [HBO]) at 170 kPa in order to analyze the effect of diving-induced hyperoxia. Bubble grades were monitored with Doppler. Cutaneous microvascular function was assessed by laser Doppler. Endothelium-dependent (acetylcholine, ACh) and -independent (sodium nitroprusside, SNP) reactivity was tested by iontophoresis. Endothelial cell activation was quantified by plasma Von Willebrand factor and nitric oxide (NO). Inactivation of NO by oxidative stress was assessed by plasma nitrotyrosine. Platelet factor 4 (PF4) was assessed in order to determine platelet aggregation. Blood was also analyzed for measurement of platelet count. Cutaneous vascular conductance (CVC) response to ACh delivery was not significantly decreased by the SCUBA protocol (23 ± 9% before vs. 17 ± 7% after; P = 0.122), whereas CVC response to SNP stimulation decreased significantly (23 ± 6% before vs. 10 ± 1% after; P = 0.039). The HBO and immersion protocols did not affect either endothelial-dependent or -independent function. The immersion protocol induced a significant increase in NO (0.07 ± 0.01 vs. 0.12 ± 0.02 μg/mL; P = 0.035). This study highlighted change in microvascular endothelial-independent but not -dependent function in highly trained divers after a single air dive. The results suggest that the effects of decompression on microvascular function may be modified by diving acclimatization.

Decreased foot inversion force and increased plantar surface after maximal incremental running exercise

Formulating the hypothesis that a maximal running exercise could induce fatigue of some foot muscles, we searched for electromyographic (EMG) signs of fatigue in the tibialis anterior (TA), peroneus longus (PL), and gastrocnemius medialis (GM) muscles. We also searched for post-exercise alterations of the stationary upright standing in normal-arched feet subjects. Healthy subjects performed a maximal running exercise. Surface EMGs of the TA, PL, and GM muscles were analysed during maximal dynamic efforts. Before and after the running bout, we measured the evoked compound muscle potential (M-wave) in TA, the maximal force into inversion (MIF), and the repartition of the plantar and barycentre surfaces with a computerised stationary platform. During maximal running exercise, the median frequency of the EMG spectra declined in TA while it remained stable in the PL and GM muscles. After the exercise, MIF decreased, and both the rearfoot plantar surface and the barycentre surface increased. We concluded that a maximal running bout elicits EMG signs of fatigue, though only in the TA muscle. It also elicits post-exercise changes in the foot position during stationary upright standing which indicates a foot eversion. These data solely concern a maximal running test and they can not be extrapolated to walking or running at a low speed.

Analysis of fatigue and tremor during sustained maximal grip contractions using Hilbert-Huang Transformation

The objective of this study was to evaluate muscle fatigue and tremor during a Sustained Maximal Grip Contraction (SMGC) using the Hilbert-Huang Transformation (HHT). Thirty-nine healthy subjects volunteered for the study and performed a 25-s SMGC. Fatigue parameters such as the relative force output (RFO) were calculated from the residual of SMGC after applying Empirical Mode Decomposition (EMD). Using the energy spectrum of the Intrinsic Mode Functions (IMF) obtained using HHT, isometric force tremor was identified from the 4 to 12 Hz region in IMF3 and IMF4. Data were analysed for five consecutive 5-s epochs to identify changes in fatigue and tremor over time. The HHT method was able to identify a greater resistance to fatigue in women compared to men (p≤0.05) and in non-dominant hands compared to dominant hands (p≤0.05). Consistent with the results for fatigue, women had less tremor than men (p≤0.05), while non-dominant hands trembled less than did dominant hands (p≤0.05). Higher levels of tremor were observed for non-fatigue-resistant subjects for both 10-15 s and 15-20 s epochs (p≤0.05). The HHT is an appropriate method to identify both fatigue and tremor during SMGC. It would be of interest to apply this method to the study the elderly or patients with neuromuscular disorders.