# Effects of Introducing Rest Intervals in Functional Fitness Training
## 4 Discussion
(2021) [40] documented mean HR values in two different types of WODs (RFT and AMRAP) of 91.7% and 91.4% HRmax, respectively, and blood lactate concentrations greater than 14 mmol-L\({}^{-1}\). This means that our FFT results were similar in terms of the mean HR of participants (\(\sim\)90% age-predicted HR), and blood lactate levels were slightly higher (13.5-15 mmol-L\({}^{-1}\)). These blood lactate values are considered very high for this type of population, indicating a high anaerobic output and representing an important physiological indicator to determine the best FFT training schedule [40]. Hence, beyond an intensity of 90% age-predicted heart rate sustained over time in this type of FFT protocol characterized by being multimodal and eliciting blood lactate levels above 10 mmol-L\({}^{-1}\), it seems that jump loss values coincide. Furthermore, it seems that having set rest intervals in FFT and FFT workouts, regardless of their length (1 min or 10 s, respectively), reduces jump capacity loss in a similar way, as reflected in different studies, although with no statistical significance. Perhaps another way of looking at this is that in both studies, the work-rest ratio for planned exercise is similar and gives rise to similar effects in terms of jump height loss. In addition, both the standard and adapted FFT workouts gave rise to a similar jump capacity reduction, which coincided with significant reduced perceived exertion 3 min after completing the workouts (\(--\)19% FFTstandard, \(--\)24% FFTadapted). The lower RPE observed in FFTadapted compared to FFTstandard (11.4 \(\pm\) 2.1 vs. 12.6 \(\pm\) 2.4, respectively) could mean the individual perceives a lower effort, as while neither the final HR nor mean HR were significantly affected, the latter was significantly lower in the rest periods. Several studies that have analyzed HR recovery during HIIT have shown HR decreases of \(\sim\)30 bpm [41] and between 39 and 57 bpm [42]. Three minutes after the workouts, blood lactate levels were lower by 1.6 mmol-L\({}^{-1}\) (\(\sim\)11%) in FFTadapted. The 11% lower blood lactate recorded in FFTadapted could evoke a reduced feeling of exertion at the general body level. In both our FFTs, blood lactate concentrations were elevated (\(>\)13 mmol-L\({}^{-1}\)). This is likely the outcome of impaired muscle performance after the two FFT protocols, as the buildup of lactate in the blood or muscle is a suitable indirect marker of intramuscular acidosis [43], which hinders muscle contraction and metabolic processes [44] ([PERSON], 2006). However, we detected significantly higher lactate values in FFTstandard (\(\sim\)11%), possibly because of a greater degree of effort and muscular fatigue. This greater effort could be explained by a lack of recovery of energy systems owing to the lack of preset rest periods. As both FFTs were similar in their duration and number of repetitions of each exercise, and had the same absolute load (kg), this means any differences observed could likely be explained by the different rest intervals and velocity at which repetitions were executed. When participants completed FFTstandard, their objective was to do this in the shortest time possible (rounds for time approach). This approach, used in many FFT protocols, allows subjects to self-regulate their energy expenditure to complete the exercise as quickly as possible. This means that the individual will set the work pace and decide whether or not to take breaks and thus dosify their efforts. Accordingly, the number of breaks taken and time rested varied widely in our FFTstandard group. With the objective to maintain the ecological validity of the study, we opted for the RFT approach to FFTstandard, as commonly used in many fitness centers around the world. Thus, we were able to observe that many participants did not take breaks, or took minimal breaks (a few seconds) between repetitions.