Stress (of a physical or mental nature) can influence homeostasis in a favorable or a negative way. More and more published works in the field of immunology signal the negative effects of physical effort, especially if it is of high or medium intensity, but repeated daily for a long period of time. On the other hand, medical statistics show more and more persisting diseases of the superior respiratory airways, digestive infectious disorders and AIDS occurring in athletes.

    Starting from these aspects, we propose to:

• Evaluate the impact that physical effort has on the human body subjected regularly (through supervised training) to such situations;
• Quantify the relation between the intensity of physical effort and the body’s ability to respond to the stress from training.

  Natural killer (NK) cells, who are involved in cellular-mediated immune processes, have multiple roles, among which: controlling the cellular proliferation, controlling the differentiation of T helper lymphocytes, direct elimination of transformed cellular categories (cancerous or virally infected). Phenotypically, NK cells are large in diameter (15 µ) and represent 5-15% of the population of circulating white blood cells.
   Often, these cells are identified by showing positive results in membrane markers such as CD₅₆, CD₁₆ and by the lack of CD₃ (marker T) on its surface. Some of the NK cells have receptors that react with the Fc fragment of G-immunoglobulin cells, onto which they adhere and thus achieve the antibody-dependent cellular cytotoxicity (ADCC).
   The well-functioning of the NK cells in the body is essential for survival, deficiencies of this population being linked with serious viral and cancerous pathology. The variable susceptibility of the NK function to the modulation from the physical effort, as it appears in literature, can be explained through the variety of types of studies: comparisons between types of sports that are opposing as training types, using uni-directional efforts, observing a certain stage of the practice and not an entire training cycle. Therefore, a category of studies do not show significant modifications of the NK activities when analyzing athletes for variable lengths of time (4-8 weeks) while conducting medium to maximum intensity effort (10). On the other hand, numerous other studies show a significant drop of NK values after high-intensity efforts, suggesting that this immune suppression could be caused mainly by prostaglandin (9) and / or associated with a decrease of glutamine in the plasma (8). The same authors warn that the low levels of LT, IL, NK are not recorded only immediately after effort, but they remain depleted for long periods of time (Nieman DC, Pedersen BK, Shephard RJ). This aspect also forms the basis for the open-window theory, which tries to explain the high risk for infections, developing tumors, self-immune diseases, minimal resistance against HIV that people who practice repeated physical training close to 90-97% intensity can have.
   The study was conducted on 15 judoka, 16 athletes and a control group of 10 students from the Faculty of Physical Education and Sports. The testing was conducted for the duration of 8 months, thus capturing all the stages of training for the same athlete. For each of the subjects, the conditions for the testing were the same: minimum three tests, training after 4 pm, and taking blood samples before training and in the first 5 minutes after training. The analysis of the blood samples was conducted at the Immunology Laboratory of the “Sf. Spiridon” University Clinic Hospital in Iaşi, and the processing of samples respected the standards for radioactive-marked NK cells, attributing to each E/T report an average value calculated according to the formula:
where: lysis % = lithic capacity of the lymphocytes; average CPM E/T = average of the three values obtained in radioactive-marked cellular recovery; SL average = average of values read in the case of spontaneous lysis; TL average = average of values recorded in total lysis. We included in the analysis only those estimates in which the average values of radioactivity, for the triplicate samples, showed a variability coefficient under 15%.
    The comparison of the area of cytotoxicity recorded after the effort (as a result thereof) with the basal cytotoxicity area before training, defines the notion of lithic individual efficiency (DELTA-AUCC), in other words the capacity of NK cells to react (positively or negatively) to stress, in this particular case to physical effort during training.
AUCC defines an area of cytotoxicity of NK lymphocytes (Area Under Cytotoxic Curve).
    Even if the sports included in the study are not similar in terms of training techniques, they quantify physical effort through an intensity index. This was also used by us in the present research, for two reasons: the first being the use, throughout a training session, of notions such as number of repeats, number of series / sets, distances, loads, duration of execution of an exercise (these are all operational elements for competition training), and they all help the coach mould the training better, based on such laboratory results.  The second reason is the mostly theoretical and less practical aspect of determining the maximum VO₂ for athletes and coach. This last test is indisputably useful for sports doctors as a prediction of performance, but we wished it to be an assessment of the reality in the training field. Following the statistical processing of the obtained data, we calculated for each case the AUCC as being the surface under the area of cytotoxicity on the scale 100:1...12,5:1 effectors / targets both before and after the effort. The analysis of data was performed for each of the two sports separately and we have obtained the following results.
   Picture 1 shows the lythic behavior of lymphocytes in judo sportsmen. We notice that the lythic values expressed as percentages DELTA AUCC are situated in the area below 26%. The significantly increased lysis is recorded in the area that corresponds to an effort of moderate intensity. As the training intensity increases, we see a tendency of decrease of the number of lymphocytes and of the lythical capacity of NK cells. This capacity remains positive (10-20%) even at an effort intensity index above 85%, but it seems that this value is insufficient for the body’s defense capacity.

Regarding the physical effort we can point out several aspects:

• Physical effort with an intensity index below 70% seems to have a beneficial effect on the defense capacity (areas 1 and 2 in Picture 1);
• Judo training performed at a rate  of 5 per week are useful to the athletes;
• At intensities of 70-80% the physical effort still has stimulating effects on the individual lysis capacity, but not at the same parameters as in the previous situation;
• Efforts of over 80% intensity index, at least in our cases, have shown a true depression in the nonspecific defense (area 3 in Picture 1);
• The association of physical effort – component of nervous stress is a factor in lowering the individual lysis capacity.

The athletes group was tested both in speed and endurance, the results being sensitively equal for the two sub-groups.
  As opposed to judoka, the values of the immune depression are more significant in their absolute value. In the speed training, negative values of the lythic efficiency were recorded for intensities above 85%, whereas in endurance training this occurred at values above 75%.
  For an index of intensity of the physical effort of 90%, the individual lythic efficiency was around minus 17% for speed tests and minus 10% for endurance.
  If the effort in training exceeds an intensity index of 95%, the values of individual lythic efficiency are observed in the area ranging up to minus 20% for endurance training and minus 27,96 for speed.
  From the data presented, it seems that the body reacts better in terms of adapting to effort if it is of an explosive nature and at an intensity of training of less than 17%.
Picture 4 shows values of the control group, data which is consistent with the one obtained for judoka and athletes.

References

Professor Paula Drosescu, MD. PhD
Faculty of Physical Education and Sports
“Al. I. Cuza” University Iasi
Professor dr.  E. Carasevici,
Assistant dr.  Fl. E.  Zugun
University of Medicine and Pharmacy Iaşi, Department of Clinical Radiology-Oncology