## 4 Discussion
Intensity levels were classified as very light (12-20 kJ/min), light (20-28 kJ/min), moderate (28-36 kJ/min), exhausting (36-52 kJ/min), and very exhausting (>52 kJ/min) [32]. According to this classification, the EE\({}_{\text{Spiro}}\) during the GBPT was defined as'very exhausting'. This is in line with previous results on perceived exhaustion after performing the GBPT (8.6 \(\pm\) 0.8 on a scale of 1-10, 10 being total exhaustion) [19]. Another study corroborated the exhausting nature of the GBPT by a blood lactate concentration of 9.9 \(\pm\) 1.5 mmol/L for female and 8.7 \(\pm\) 1.6 mmol/L for male elite team-handball players [38]. The agreement in the intensity level of the current EE\({}_{\text{Spiro}}\) with these previous findings supports the accuracy of the current EE\({}_{\text{Spiro}}\). In contrast, the current EE\({}_{\text{LPM}}\) (20.46 \(\pm\) 3.26 kJ/min) was around the threshold between'very light' and 'light', which is comparable with walking. This discrepancy with the simultaneously determined EE\({}_{\text{Spiro}}\), reported blood lactate levels [38], and perceived exhaustion [19] demonstrated that the EE\({}_{\text{LPM}}\) underestimated the EE dramatically. It is highly unlikely that the intensity level during the GBPT, a validated test that reflects the physical demands in team handball competition, performed by experienced athletes, is comparable with EE in walking. It should be considered that the intensity level refers to time-normalized EE and that the GBPT includes breaks (i.e., periods where EE\({}_{\text{LPM}}\) equals 0 kJ, affecting the time-normalized EE) whereas the intensity classification refers to walking without breaks. This may explain the comparability between EE per minute during the GBPT and walking. Expecting that the EE\({}_{\text{LPM}}\) were estimated accurately in walking and running, the findings underline the great energetic contribution of team handball-specific actions (e.g., passing) and vertical displacements (e.g., jumps) to the total EE in team handball. To exclude another potential challenge, the authors point out that the valid range of acceleration values in the metabolic power model [9] for EE\({}_{\text{LPM}}\) estimation is limited to approximately \(\pm\)4.42 m/s\({}^{2}\). Exceeding this range of \(\pm\)4.42 m/s\({}^{2}\) could lead to estimation errors [22]. However, in the present study, the accelerations and decelerations exceeded the valid range only in 0.03 \(\pm\) 0.06% of the total test duration. For all participants in the present study the maximum in deceleration was \(-\)4.84 m/s\({}^{2}\) and in acceleration 5.01 m/s\({}^{2}\). Therefore, we conclude that the acceleration range in the calculation of EE\({}_{\text{LPM}}\) was no limitation. The differences between EE\({}_{\text{Spiro}}\) and EE\({}_{\text{LPM}}\) are in agreement with previous studies in team sports [11; 12; 13]. In the present study, we found a smaller EE of \(-\)66 \(\pm\) 12% in EE\({}_{\text{LPM}}\) compared with gross EE\({}_{\text{Spiro}}\) and \(-\)63 \(\pm\) 12% compared with net EE\({}_{\text{Spiro}}\) (after subtraction of REE). Similarly, EE\({}_{\text{LPM}}\) was \(-\)54 \(\pm\) 9% smaller in soccer using a comparable test design of a soccer-specific circuit test [12]. In test designs with reduced specificity (incremental treadmill running), the underestimation of EE\({}_{\text{LPM}}\) compared to EE\({}_{\text{Spiro}}\) was much smaller (\(-\)13 to \(-\)16%) [8]. Another aspect is the involvement of the ball because it was found that EE\({}_{\text{Spiro}}\) increased by 9% when involving a ball, whereas EE\({}_{\text{LPM}}\) increased only by 1% [7]. We suggest that the difference between EE\({}_{\text{LPM}}\) and EE\({}_{\text{Spiro}}\) increases with more specificity; consequently, the sport-specific actions play a major role in the estimation of EE in team sports. Physical collisions were another explanation for the difference between \(\text{EE}_{\text{LPM}}\) and \(\text{EE}_{\text{Spiro}}\) in collision-based activities in rugby [13].