# Effects of Introducing Rest Intervals in Functional Fitness Training
## 4 Discussion
Several studies have shown that for a given absolute load (kg), subjects can show different velocities, meaning that this load can represent a different relative intensity (%) depending on the velocity reached by each subject in each exercise [13; 14; 15; 16]. Thus, it could be that when the participants executed FFTstandard, because of the scarce rest intervals taken, execution velocities were reduced. This gives rise to a greater extent of fatigue, making the subject apply less force (N) on that load and thereby reducing the net force value. However, subjects taking three 1 min breaks could attain greater execution velocities with the same load, reducing fatigue and allowing the recovery of neuromuscular capacity to apply more force, and were thus able to complete the same number of repetitions in less time. This would be due to the recovery of over 70% of phosphocreatine levels in each minute of rest [21]), thereby reducing metabolic acidosis due to a lower glycolytic rate. This reasoning is what probably led to significantly reduced blood lactate levels when completing FFTadapted (FFTadapted = 13.5, FFTstandard = 15 mmol\(\cdot\)L\({}^{-1}\)). In this way, the duration of FFTadapted could be similar to that of FFTstandard. According to these findings, we would have to ask ourselves whether executing a FFT without controlling rest interval duration really has any benefits, or whether the greater effort and fatigue could modify the biomechanics of movement leading to injury [23]. Many of the FFT exercises are technically demanding, generating tension and overloading of the shoulder and lumbar region [22]. In the present study, the durations of both FFTs were almost identical, meaning that the velocity of exercise execution was faster in FFTadapted. This indicates that exercises such as the power clean or snatch, which require high power levels [45], are probably executed with greater technical efficacy. Hence, the introduction of pre-established, controlled rest intervals could be recommended to guarantee an adequate intensity level, less fatigue during exercise performance, and reduced risk of injury. High blood lactate levels (>16 mmol\(\cdot\)L\({}^{-1}\)) [28; 46] have been described after completing FFT workouts, which has been linked to situations of extreme fatigue. Many studies have identified situations of rhabdomyis related to this type of high-intensity effort [47; 48; 49]. Hence, it is likely that all-out training through FFT tactics such as AMRAP, RFT, or EMON (every minute on the minute) could have adverse health impacts [11]. In a recent study, [PERSON] et al. (2019) [46] tried to determine whether self-regulation of training intensity based on RPE is a reliable method to control work intensity during metabolic conditioning sessions of FFT. To this end, a session was completed based on AMRAP under two different conditions: (1) all-out or (2) self-regulation of intensity based on an RPE of 6 (hard) on the Borg CR-scale. Their findings indicated significantly reduced RPE and blood lactate levels at all time points when exercise intensity was self-regulated [46]. More work is needed to address the impacts of incorporating pre-established recovery times in these types of methods (RFT, AMRAP, EMON) to ensure an adequate balance between intensity and fatigue that will reduce the risk of injury. Furthermore, to address a limitation of this work, it would be interesting to be able to measure systolic and diastolic blood pressure before and after the FFT session in this type of study. In addition, due to the high intensity of exercise in this type of FFT session, an exercise tolerance test to rule out cardiovascular abnormalities and a previous blood profile of each participant would be interesting to perform to properly categorize the sample.