Great diversity exists within the strength training world with regards the amount of rest that should be taken between sets. Within bodybuilding circles, it is believed that utilising shorter rest periods will place greater stress on the muscles and induce greater metabolic fatigue, thereby stimulation hypertrophy and muscle gain. Furthermore, a multitude of set-extending techniques, in which minimal rest is taken, are frequently employed by those with physique oriented goals to increase muscle damage. These include ‘dropsets’, ‘supersets’, ‘giant sets’, ‘rest-pause sets’, and more. On the other hand, powerlifters and ‘traditional’ athletes often utilise longer rest periods in order to maintain power output and number of repetitions per set, as well as reducing the risk of injury. Therefore, this article will review the scientific literature in which the effect of rest period duration upon strength, hypertrophy, muscular endurance, and physiological responses to training in both the short and long term.
Firstly, it is apparent that conflicting results have been published in the available scientific literature with regards the effect of rest periods upon strength, defined here as maximal exertion over a short period i.e 1 rep max (1RM). In agreement with general consensus, the majority of these studies have demonstrated that longer rest periods resulted in greater increases in strength compared to shorter rest periods.
Pincivero and colleagues1 examined the isokinetic strength of 15 male subjects divided into two groups, the first utilised 40 second rest periods (2:1 rest to work ratio) and the second utilised 160 second rest periods (8:1 rest to work ratio). Each subject trained one leg three times per week for four weeks, performing four sets of 10 during each session and increased training volume by one set each week. From this study, it was demonstrated that longer rest periods resulted in greater improvements in peak power and torque, particularly of the hamstrings. However, this increased strength when a longer rest is taken did not carry over into an improvement functional performance in the long jump. Furthermore, the participants in this study were untrained or detrained college males that had not participated in resistance exercise within the last 6 months. A larger study in weight trained males, in which participants undertook high volume training for 5 weeks and were divided into 3 groups (3 mins rest, 5 mins rest, 30 second rest), discovered that peak power, total work and 1RM increased in all groups. However, it was determined that 1RM increased in group 1 (7%) to a greater extent than group 3 (2%), although it was proposed that high volume training may not be dependent upon rest intervals in the short term.
More recently, Matuszak et al2 examined the acute responses of 1, 3, and 5 minute rest periods upon back squat 1RM in recreationally strength trained lifters. The authors observed an increased repetition failure rate in the 1 minute rest period group compared to the 3 and 5 minute groups, and that little difference was observed between the 3 and 5 minute groups. However, these trends were found to be non-significant and it was concluded that the duration of rest period had no significant effect upon squat 1RM. It was proposed that, as 1RM squats lasting <6 seconds predominantly utilise the phosphagen system and that phosphocreatine can be replenished within 30 seconds, rapid replenishment of phosphocreatine may have led to low failure rates in all rest period groups. These findings were supported by Buresh and colleagues3 who determined that, over 10 weeks, no difference in strength gains were observed between 1 minute and 2.5 minute rest period groups for both squat and bench press, although a slightly greater increase in longer rest groups were found.
Contrary to the previously described studies, Ahtiainen et al4 compared the effect of 2 minute rest periods and 5 minute rest periods during lower body training upon a number of variables in 13 recreationally trained men. Interestingly, they determined that the shorter rest period groups lifted significantly heavier loads than the longer rest period groups during both the leg press and the squat, and that increased maximal leg extension force was observed in the short rest group. Nonetheless, it was also found that the greatest increases in maximal isometric force occurred when long rest periods were utilised, and that there was no significant difference in unilateral 1RM between groups.
To summarise the findings regarding the effect of rest period duration upon strength, the majority of the data would suggest that longer rest periods are superior to shorter rest periods if maximal strength is the goal. Although conflicting data exists, it is likely that differences in definitions of ‘short’ and ‘long’ rest periods, study duration, sample size, and study design play a significant role in this ambiguity.
With regards muscular endurance, characterised in this article as the number of repetitions performed per set, a lower number of repetitions performed and greater decline in number of repetitions has been demonstrated with shorter rest periods in both the squat and bench press5,6,7. Miranda and colleagues8 have also demonstrated similar findings when subjects performed multiple exercises during a typical ‘Back & Biceps’ workout. However, although it was demonstrated that 3 minute rest periods allowed for the performance of more volume when performing the squat, no significant difference was found between 1 and 2 minute rest periods, which may be due to the greater endurance of lower body muscle groups that are more frequently utilised in daily activity7. Furthermore, these studies also discovered that the decline in repetitions per set continues as rest duration gets shorter up to 1 minute rest periods, after which (30 second rest) no difference in number of achievable repetitions is observed.
After multiple sets, plateaus in the decline in the number of repetitions performed per set have been identified, and this may be due to rapid ATP replenishment via phosphocreatine, although accumulation of hydrogen ions may prevent achievable volume returning to that of early sets5. It is likely that rest intervals taken between sets later in a workout will be longer than earlier in the workout due to fatigue9. Additionally, it is likely that rest periods of 1 minute are insufficient to fully replenish anaerobic energy sources and to fully restore neural drive8. Shorter rest periods may also lead to greater lactate and hydrogen ion accumulation and thus fatigue6, although conflicting data regarding this exists4.
The effect of rest interval duration upon hypertrophy may be difficult to measure, as the majority of the published studies, in which the effect of rest period duration has been examined, are performed over a short time period (5-10 weeks) and therefore significant changes in muscle mass are unlikely to be significant in trained individuals. However, it has been observed that longer rest groups (2.5 mins) produced greater increases in arm and thigh cross-sectional area over ten weeks, a commonly employed measure of hypertrophy3. However, Ahtiainen et al4 observed no significant difference in quadriceps cross-sectional area when either 2 or 5 minute rest intervals are utilised.
Although acute changes in hormonal response to rest period duration in short term studies may not have a significant effect upon performance, strength or hypertrophy, these changes may influence fatigue. Furthermore, if these changes are maintained in the long term, they may significantly affect strength and hypertrophy. Ahtiainen and colleagues4 found increased growth hormone, serum testosterone, free testosterone and cortisol after three months of training with short rest intervals (2 min) compared to longer intervals (5 min). Although the increase in testosterone and growth hormone may suggest that shorter rest periods stimulate greater anabolic signalling, this may be counteracted by the increase in cortisol production. However, although Buresh et al3 identified increased levels of testosterone and cortisol after 1 week of training with short rest intervals (1 min), these differences were not sustained after 5 or 10 weeks, suggesting no change in long-term hormone production, and were significantly affected by inter-individual variation.
To conclude, in theory, short intervals may be beneficial to hypertrophy, by creating significant metabolic fatigue, and local muscular endurance, by increasing mitochondrial and capillary density, increasing buffer capacity, and promoting shifts in muscle fibre composition9. Nonetheless, there is little available data to support these hypotheses. However, one advantage of shorter rest periods, including the use of set-extending methods such as supersets, is that they will typically allow for the more rapid completion of workouts10. From the scientific literature it is apparent that shorter rest periods are detrimental to strength and reduce achievable volume, force and power output. Also, it must be ensured that exercise form and technique does not suffer as a result of fatigue caused when short rest periods are utilised10. The adaptive responses and negative consequences as a result of the frequent use of short rest intervals demonstrate the need for periodisation within training programmes to allow for recovery and to prevent fatigue11.
However, the metabolic stress associated with short rest periods may be counteracted by the reduced strength capacity and performance, and therefore longer rest periods may be required for optimal hypertrophy. The scientific data indicates that longer rest intervals are superior for the maintenance of strength and volume, and may be preferable when larger muscle groups are trained, due to greater fatigue12. Nonetheless, despite the recovery of strength and maximal force production, and the optimisation of mechanical tension with longer rest intervals, metabolic stress is compromised. Therefore, for the purposes of maximal hypertrophy, moderate rest periods (~2 minutes) may be optimal to balance metabolic fatigue and the maintenance of volume and strength. However, it is apparent that the duration of rest intervals between sets will depend upon training intensity, training goals, fitness level and the energy system being utilised9.
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