Abstract: This study examined the influence of intensity (%1RM), tonnage (sets x repetitions x load), rate of fatigue (percentage decrement in repetitions from set-to-set), work rate (total tonnage per unit of time), rest interval (time between sets), time under load, and session duration on session rating of perceived exertion (sRPE: Borg CR-10 scale). Here, participants performed a standardised lifting session of five exercises (bench press, leg press, lat pulldown, leg curl and triceps pushdown) as either: A) 3 sets x 8 repetitions x 3 min recovery at 70% 1RM; B) 3 sets x 14 repetitions x 3 min recovery at 40% 1RM; C) 3 sets x MNR (maximum number of repetitions) x 1 min recovery at 70% 1RM; D) 3 sets x MNR x 3 min recovery at 70% 1RM; E) 3 sets x MNR x 1 min recovery at 40% 1RM; or F) 3 sets x MNR x 3 min recovery at 40% 1RM. The sRPE for session A (4 +/- 1) was significantly higher than session B (2.5 +/- 1), despite matched tonnage. Protocols involving MNR showed no significant difference in sRPE. Work rate was the only variable to significantly relate with sRPE (r = 0.45). Additionally, sRPE at 15 min post-exercise (5 +/- 2) was not different to 30 min post-exercise (5 +/- 2). In resistance training with matched tonnage and rest duration between sets, sRPE increases with intensity. In sets to volitional failure, sRPE is likely to be similar, regardless of intensity or rest duration between sets.
Alex’s Notes: When designing resistance training programs, it is important to understand how the different variables affect perceived fatigue. To this end, total tonnage (sets x repetitions x load), intensity (% 1RM), number of repetitions in each set, and the recovery time between sets were manipulated in ten male team-sport athletes with at least 12 months of resistance training experience. Over the course of six uninterrupted weeks, the participants completed six workouts (1 per week @ the same general time of day) with one of the following protocols:
- 3 sets x 8 reps x 3 min recovery @ 70% 1RM
- 3 sets x 14 reps x 3 min recovery @ 40% 1RM (matched tonnage with A)
- 3 sets x maximum number of repetitions (MNR) x 1 min recovery @ 70% 1RM
- 3 sets x MNR x 3 min recovery @ 70% 1RM
- 3 sets x MNR x 1 min recovery @ 40% 1RM
- 3 sets x MNR x 3 min recovery @ 40% 1RM
The MNR means that the subject performs the set to voluntary failure. All the workout sessions included the same five exercises: bench press, leg press, lat pulldown, leg curl, and triceps pushdown. The time under load was kept constant and involved a 2-second concentric phase, 1-second pause, 2-second eccentric phase, and 1-second pause. The participants rated their perceived exertion (RPE) on the Borg CR-10 scale 15 and 30 minutes after each workout.
Which do you think would be most difficult?
I would probably bet that the MNR @ 70% 1RM with 1 minute of rest would be the most challenging. And sure enough I would only be partially correct. All the MNR sessions were significantly more difficult than the matched tonnage sessions (A & B), but they were not significantly difference from one another, suggesting that when training to failure, intensity is not the primary mediator of perceived fatigue. Conversely, during the matched tonnage workouts, the 70% 1RM was significantly more fatiguing than the 40% 1RM workout, suggesting that intensity is the primary mediator of fatigue when tonnage and rest time are held constant. There were also no significant differences between the RPE at 15 or 30 minutes post-workout (in fact they were the exact same).
Session C had the shortest session duration at 42 minutes, compared to 50-70 minutes in the other sessions. This also led to session C having the greatest work rate (tonnage/minute), and this variable was the only one found to be related to the RPE during the MNR sessions. On the other hand, intensity, repetitions, time under load, and session duration had significant associations during the matched tonnage sessions.
When training to failure, fatigue is only dependent on the work rate – how much weight you move in a given time. This does not mean that the physiological response and muscular adaptations would be equivalent; it only means that this variable will affect how difficult the session is perceived to be.
When training with more boundaries, such as when using the double-progressive overload method of progression, a greater intensity increases, while a greater number of repetition, time under load, and session duration reduces perceived exertion. But wait, how can more reps and co. make the workout seem easier? Remember that none of these variables exist in a vacuum; if you increase your repetitions and time under load then your intensity will have to be reduced and vice-versa. Also, for clarification, the double-progressive method basically means that if you were doing 3 sets of 8 reps, you would stop at 8 reps on every set even if you could do more, and once you were able to do 3 sets of 8 with a given weight, you would increase the weight and repeat in future sessions.