Landfarming

The time taken between sets is referred to as the rest interval, or rest period. Rest intervals can be classified into three broad categories: short (30 seconds or less), moderate (60 to 90 seconds), and long (3 minutes or more) (656). Research demonstrates that rest interval length has distinct effects on the acute response to resistance training, and these responses have been hypothesized to affect chronic hypertrophic adaptations.

Short rest intervals have been shown to markedly increase metabolite accumulation. Ratamess and colleagues (603) found that 30-second rest

intervals reduced training volume by more than 50% over the course of 5 sets at 10RM, and marked decreases in load were seen in each subsequent set. Thus, metabolic enhancement is achieved at the expense of reduced mechanical tension, resulting in the need to progressively reduce the amount of loading over subsequent sets to sustain performance in a given repetition range.

Long rest intervals provide a sustained ability to maintain mechanical tension throughout each successive set. Strength capacity has been shown to be largely preserved over 3 sets with rest intervals of 3 minutes or more (383, 603). However, metabolite accumulation diminishes with increasing rest between sets, particularly with respect to lactic acid buildup (4).

Moderate rest periods are believed to provide an ideal compromise between metabolic stress and mechanical tension. A hypertrophy-type workout in which people rested 90 seconds between sets showed significantly greater increases in blood lactate concentration and reductions in pH compared to a strength- type workout with 5 minutes of rest between sets (527). With respect to the effect on loading, Medeiros and colleagues (485) found that using 60 second rest intervals required a reduction of 5% to 10% in each successive set to allow for the maintenance of 8- to 12RM loads in resistance-trained subjects. Because moderate rest intervals induce a favorable metabolic environment without substantially compromising mechanical forces, a rest interval of 60 to 90 seconds is generally prescribed for maximizing hypertrophy.

Despite the commonly accepted belief that hypertrophy-oriented routines

benefit from moderate rest between sets, only a handful of studies have directly investigated the effect of rest intervals on muscle growth over time. In a

crossover design, Ahtiainen and colleagues (20) assessed the hypertrophic impact in well-trained men of taking 2-minute versus 5-minute rest intervals while performing volume-matched work bouts of lower-body resistance exercise. Training was carried out over two separate 3-month periods, in which subjects rested 2 minutes in one of the periods and 5 minutes in the other. No significant differences in muscle cross-sectional areas were seen between conditions. The study had several strengths including a randomized crossover design (which substantially increases statistical power), the inclusion of trained subjects, and the use of magnetic resonance imaging to measure muscle growth. The primary issue with the study is that the 2-minute rest period is longer than what is generally advised for hypertrophy-type training. Specifically, the impact on metabolic stress diminishes with longer rest periods, and in fact, blood lactate levels were not significantly different between the groups in the study, which may have compromised anabolic signaling.

Buresh and colleagues (108) carried out a study in which 12 untrained people performed their workout with either 1 or 2.5 minutes of rest between sets. This study showed that longer interset rest intervals produced superior hypertrophy in the arms and a trend for greater growth in the legs compared to training with shorter rest intervals. Although the results may seem compelling, it should be noted that muscle cross-sectional area was determined by anthropometric means (i.e., surface measurements), which can be quite unreliable and thus compromise accuracy. Further confounding matters is the small number of subjects (only 6 in each group) and the fact that subjects were not resistance trained.

Key Point

Although rest periods of 60 to 90 seconds induce a favorable metabolic environment for achieving hypertrophy, research indicates that resting at least 2 minutes between sets provides a hypertrophic advantage compared to shorter rest periods because of the ability to maintain greater volume load.

In a novel research design, DeSouza and colleagues (172) randomized 20 resistance-trained men to either a group that used a constant rest interval or a group that used descending rest intervals. All of the men began by performing 3 sets of 10 to 12 repetitions with 2 minutes of rest for the first 2 weeks.

Thereafter, the length of the rest interval progressively decreased to 30

seconds in the descending rest interval group over an ensuing 6-week period, whereas that of the constant rest interval group remained the same. After 8 weeks, both groups had significantly increased hypertrophy of the upper and lower extremities; no significant differences were noted in rest interval

conditions despite a reduction in training volume for the descending group. A follow-up study using essentially the same protocol but with subjects receiving creatine supplementation again found no significant hypertrophic differences between constant and descending rest intervals (715). Interestingly, effect sizes were substantially greater for descending versus constant rest intervals in the cross-sectional area of both the upper arm (2.53 vs. 1.11, respectively) and thigh (3.23 vs. 2.02, respectively).

My lab recently carried out a study investigating the impact of short versus long rest intervals on hypertrophy (651). Subjects were randomized to perform multiple sets of 7 exercises for the major muscle groups of the upper and lower body with either 1 or 3 minutes of rest between sets. After 8 weeks, the longer rest condition produced greater increases in the anterior thigh muscles, and a strong trend for greater increases was noted in the triceps brachii. Beneficial effects of longer rest periods on hypertrophy were attributed to the ability to maintain a higher volume load over the course of the study.

Table 3.6 provides a summary of the research related to rest interval length and muscle hypertrophy.

Rest Interval Length

Practical Applications

Despite a theoretical concept that shorter rest intervals produce superior muscular adaptations, current research does not support such a

contention. In fact, longer interset rest periods may enhance hypertrophy by allowing for maintenance of a greater volume load. Thus, resistance training protocols should generally provide rest periods of at least 2 minutes to maximize the hypertrophic response. That said, consistently training with shorter rest intervals has been shown to promote adaptations that ultimately facilitate the ability to sustain a significantly higher mean percentage of 1RM during training (384). These adaptations include increased capillary and mitochondrial density as well as an improved capacity to buffer hydrogen ions and shuttle them out of muscle, thereby

minimizing performance decrements. Conceivably, this could allow maintenance of volume with greater metabolic stress, ultimately leading to greater muscle protein accretion. It therefore seems prudent to include training cycles that limit rest intervals to 60 to 90 seconds to take

advantage of any additive effects of metabolic stress if they indeed exist. In particular, high-repetition sets may benefit from short rest periods given the reduced need to exert maximal force and the greater potential for realizing the adaptations associated with improved buffering.