The Validity of External:Internal Training Load Ratios in Rested and Fatigued Soccer Players

Akubat, I., Barrett, S., Lapuente Sagarra, M., Abt, G.

Purpose:
The aim of this study was to investigate the relationship between external:internal training load ratios and fitness, and to assess the impact of fatigue on these ratios.

Method:
Ten soccer players participated in a lactate threshold test followed by two soccer simulations (BEAST90mod) conducted 48 hours apart. Recovery (Total Quality of Recovery, TQR) and muscle soreness (Delayed Onset Muscle Soreness, DOMS) were measured before each trial. Internal Training Load (TL) was assessed using the individualized training impulse (iTRIMP) method, while external load was measured in terms of total distance (TD), high-intensity distance (HID), PlayerLoadTM (PL), mean metabolic power (MMP), and high metabolic power distance (HP). External:internal load ratios were calculated, and their relationships with velocity at lactate threshold (vLT) and velocity at Onset of Blood Lactate Accumulation (vOBLA) were examined in both trials, considering changes in these ratios.

Results:
Significant changes were observed in Total Quality of Recovery and DOMS, indicating notable changes in fatigue levels. There were varying decreases in TL from trial 1 to trial 2. Moderate increases in ratios for TD:iTRIMP, PL:iTRIMP, and MMP:iTRIMP were noted, but only small to trivial changes were observed for HP:iTRIMP and HID:iTRIMP. In rested conditions, all ratios showed significant relationships with vLT and vOBLA. However, under fatigue, the relationships between vLT and HID:iTRIMP, PL:iTRIMP, HP:iTRIMP, as well as between vOBLA and TD:iTRIMP, PL:iTRIMP, and MMP:iTRIMP, became weaker.

Conclusions:
Acute changes in external:internal training load ratios have implications for their use as fitness measures and indicators of fatigue. These findings underscore the importance of considering fatigue levels when interpreting training load ratios.