## 4 Discussion  
The aim of this study was to investigate the changes in the quadriceps femoris muscle rate of torque development scaling factor (RTD-SF) following unilateral isometric training. The training intervention included either electrostimulation or voluntary exercises (EMS and VOL, respectively). The main findings regarding our first hypothesis are as follows: (1) both interventions induced similar decrements in RTD-SF (approximately 15%); (2) Intercept was increased following both training modalities (22 and 17% for EMS and VOL, respectively) but due to the high variability the change was significant only following EMS; (3) both interventions increased Tmax by \(\sim\)30%; and (4) comparable increments, although of lower magnitude (14%), were observed for RTDmax. Our second hypothesis was not confirmed because the cross-education effect to the non-trained leg was observed only for the EMS group. As was hypothesized, the applied training interventions had a significant effect on the RTD-SF. In fact, to our surprise, both EMS and VOL induced a decrease in RTD-SF, which could be partly explained by a higher relative increase in Tmax than in RTDmax. Although previous studies revealed that the RTD-SF protocol could be used to discriminate between participants of different ages [14], sexes [13], fatigue or physical activity levels [11; 15], or inter-limb asymmetries [7; 39], currently no published data are available regarding how strength training interventions affect the RTD-SF. The study that investigated changes in RTD-SF following exercise intervention was conducted on active older adults and it involved a 6-week high-intensity interval cycling intervention [12]. Hence, the authors reported a 34% improvement in RTD-SF (i.e., a higher slope) of QF in the exercise group  
Figure 4: Standardized mean differences (90% confidence intervals) for all dependent variables between the EMS and VOL group (ES = EMS mean - VOL mean/SD both). The shaded area represents a trivial difference (ES from -0.20 to 0.20). Tmax—maximum torque; RTDmax—maximum rate of torque development; RTD-SF—rate of torque development scaling factor. but not in controls. This is not surprising since robust improvements in explosive capacities are expected following both high- and low-speed dynamic exercises and ballistic isometric exercises performed against lower load (e.g., <60% of maximum torque) and with the intent of rapid torque production [5]. In the current study, it seems that rapid torque generation was unaffected by training intervention for intensities < 50% MVC (Figure 2). However, a visible decrease in rapid production can be observed for higher intensities (50-80% MVC) that we suspect resulted in lower RTD-SF when compared to pre-test values. Considering that isometric exercises used in this study were not as ballistic as in the RFD-SF assessment protocol, the applied training modalities had a significant negative impact on neuromuscular quickness assessed through RTD-SF. This finding could be of importance for researchers investigating muscle function and for coaches working with speed-trained athletes who may consider using moderate-intensity isometric contractions in their training or rehabilitation routines as well. Intercept is the variable that has mostly stayed unreported or not discussed as it was considered to provide no additional information [1, 2, 6, 12]. A study that investigated how cognitive fatigue affects RFD-SF presented rarely reported results on Intercept that remained unaffected [16]. [PERSON] et al. [2] speculated that a higher Intercept together with the same RFD-SF could indicate superior quickness across the range of contraction intensities, which is only partly the case in our study since Intercept increased while the slope, i.e., RFD-SF, declined. Nevertheless, more studies are needed to answer the question on the physiological and potentially clinical relevance of the Intercept.