The endurance training effect on the oxygenation status of an isometrically contracted forearm muscle
The aim of the study was to find the influence of training on the oxygenation status of a forearm muscle during submaximal isometric contraction. Six subjects performed a test of isometric contraction of a forearm muscle by continuous pressing of a handgrip dynamometer with a force of 15 kp, until exhaustion. The continuous measurements of oxygen saturation (%) (OXY), concentration of oxygenated haemoglobin (μM) (OXYHb), deoxygenated haemoglobin (μM) (DEOXYHb) and total haemoglobin (μM) (TOTHb) in blood, which passed through the muscle, were made by the near infrared spectroscope Oxymeter 96208 (ISS, USA). This test was repeated before and after the four weeks training period, which consisted of 5 continuous isometric contractions of 30 s at the beginning and of 1:15 min during the last week. Training did not significantly influence maximal isometric force (55.5 ± 10 kp before, 60.2 ± 9 kp after). On the other hand, the duration of isometric contraction increased from 271 ± 117 s to 388 ± 152 s (P < 0.05). Subjects were substantially different in duration of muscle contraction and also in oxygenation status during the contractions. Therefore, the relationship between these parameters and the training effect was calculated. The training effect was represented as the difference between the duration of muscle contraction before and after the training period. This parameter significantly correlated with relative oxygen saturation (r=-0.88; P < 0.05) and with relative concentration of deoxygenated haemoglobin (r = 0.87; P < 0.05). These results demonstrated the importance of individual training adaptations of forearm muscles. The increase of the duration of submaximal isometric contraction, as a training effect, can be dependent on larger muscle deoxygenation.