Andrzej Czerwiński

Background: Exercise in the cold is an attractive option for many athletes. Erythrocyte aggregation, as one of the main rheological parameters, constitutes an important indicator of microcirculation and oxygen transport capacity in the human body. Acute exercise and environmental cold may alter erythrocyte aggregation. We compared immediate hematological, aggregation, metabolic, and hormonal responses to progressive shuttle run exercise in a cold chamber and outdoors. Methods: This exploratory parallel-group analysis included 30 young healthy male students allocated to exercise in a climatic chamber at −10 °C (n = 15) or outdoors at 18 °C (n = 15). Blood was collected before and immediately after exercise. Group × time interactions were assessed using repeated-measures ANOVA and within-group comparisons used Bonferroni adjustment. Results: Erythrocyte amplitude of aggregation (AMP) showed a significant group × time interaction (p = 0.0014). In the paired analysis, the between-group difference in AMP change was −3.24 au (pointwise 95% CI −5.12 to −1.36). Lactate showed a nominal interaction (p = 0.016). Within the experimental group, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, aggregation index (AI) and lactate increased, whereas AMP and aggregation half-time (T½) decreased (all p < 0.001). Estimated plasma-volume change did not differ significantly between settings. Conclusions: Exercise in the cold-chamber setting was associated with a greater reduction in the optical aggregation amplitude. Further studies are needed to clarify the contribution of temperature and the physiological significance of these changes.

The study aimed to determine the effect of acute, one-time physical effort performed under different environmental temperature conditions on erythrocyte deformability in healthy young men. This exploratory randomized parallel-group study involved 30 men randomly assigned to an experimental group exercising at −10 °C in a climatic chamber and a control group exercising under thermoneutral outdoor conditions. Erythrocyte deformability was assessed using the elongation index (EI), reflecting erythrocyte elasticity and the ability to pass through microcirculation vessels. Participants performed an incremental 20 m shuttle run test. Venous blood samples were collected before and immediately after exercise, and erythrocyte deformability was analyzed using a Lorrca analyzer across a shear stress range of 0.30–60.00 Pa. A two-factor repeated-measures analysis of variance was applied. An increase in EI after exercise was observed in both groups, predominantly at higher shear stress values, indicating enhanced erythrocyte deformability under conditions of increased shear forces. However, the magnitude of post-exertion changes differed between groups. At lower shear stress levels (0.30 Pa and 0.58 Pa), EI tended to decrease after exercise. These findings indicate that a single bout of physical effort influences erythrocyte deformability, while the potential effects of cold exposure on this response remain uncertain and warrant further investigation.

This paper presents the results of an experimental study of the parametric vibrations of a pulsating tensioned string. At certain amplitudes and frequencies of excitation in the form of a variable axial force, dynamic instability arises in the system, and transverse vibrations are excited. A non-contact measurement system based on high-speed cameras and an image analysis method was used for the measurements. The eigenfrequency values of the system were determined, and the different types of resonant vibrations arising were examined in detail. In each case, the mode shape of the vibrations, motion trajectories, time traces, spectra and phase portraits of the vibrations were studied. Vibrations in single-mode simple resonances with periodic type and in-plane motion, spatial non- -periodic vibrations in combination resonances and also cases of very complex non-periodic vibrations with spatial motion when different types of parametric resonances excite simultaneously were identified.