Introduction and objective:
The study aimed to evaluate the physiological stress response, i.e. internal load to intermittent and continuous exercise performed during the treadmill running in professional female soccer players, and additionally to determine the most appropriate method for assessing load in the athletes.

Material and methods:
Six professional female athletes (age 25.3±1.8 years, height 168.4±2.7 cm, weight 64.8±5.8 kg, maximal oxygen consumption (V˙ O2max) 64±4.1 ml۰kg-1۰min-1, and heart rate (HRmax) 195±1.8 b.p.m.) performed a series of preseason treadmill tests. HR and V˙ O2max were measured in the athletes during intermittent load (increase and decrease of running time and treadmill speed) and an incremental load (gradual increases running time, treadmill speed and a treadmill incline angle). Banister’s, Edwards’, Stagno’s and Lucia’s training impulse (TRIMP) quantification methods were used to assess internal load. The relationships between V˙ O2max and above-mentioned TRIMPs load indicators were calculated using Pearson’s correlation coefficient.

Results:
Large, very large and near perfect correlations between TRIMP and V˙ O2max were observed during intermittent and incremental load (range r = 0.712 – 0.852 and r =563 – 930; p < 0.05, respectively). Correlations between other TRIMPs and V˙ O2max demonstrated moderate, small and negative small relationships.

Conclusions:
Changes in HR and oxygen consumption registered during intermittent or gradually increasing load conditions could be evaluated using the TRIMP method for both types of activities, and this method could potentially be useful for the testing of high-intensity intermittent physical fitness of players before the soccer season.