The workout with higher rep lower load sets (30FAIL) was equally effective in stimulating muscle (myofibrillar) protein synthesis as a workout with low rep high load sets (90FAIL) 1. But more notably, the high-rep low load workout (30FAIL) resulted in a more prolonged muscle protein synthetic response and a greater elevation of muscle protein synthesis rates than the low rep high load workout (90FAIL) 24h after exercise, and also induced a greater stimulation of anabolic signalling pathways 1.

However, this study was an acute study with measurements taken for only 24 hours after one single workout bout. This doesn’t tell us whether higher rep sets would lead to long term increases in muscle mass, which is what we are ultimately interested in. Well, the same research group just published an actual 10 week training study 2 to find the answer to this nerve-itching question….

Training program

The subjects in this study were healthy young men (21 years old, 5ft 7in tall, 162 lb), who were recreationally active with no formal weight-lifting experience or regular weight-lifting activity over the last year.

The training program consisted of unilateral knee extension training performed 3 times per week for 10 weeks. Each leg was randomly assigned to one of three workouts:

1) one set performed to failure at 80% of 1RM (80%-1) – 8-12 reps

2) three sets performed to failure at 80% of 1RM (80%-3) – 8-12 reps

3) three sets performed to failure at 30% of 1RM (30%-3) – 20-30 reps

While the previous single workout study used an intensity of 90% of 1RM 1, in this training study the researchers chose 80% of 1RM, because this is touted as being optimal for muscle grown. Also, training at 90% of 1RM non-stop for 10 weeks would be pretty though and not representative of a typical muscle growth training program.

Each participant trained both legs and was therefore assigned to two of the three possible training conditions. Immediately after each training session subjects consumed a high quality protein (PowerBar Protein Plus, 360 kcal, 3.5g leucine 30g protein, 33g carbohydrate, 11g fat; Nestle Nutrition) in conjunction with 300ml of water to standardize the post-exercise meal and maximize training adaptations.

Before and after the training program, whole muscle volume was measured (using magnetic resonance imaging) and changes in muscle fiber area were determined. Knee extension performance was measured by 1RM, maximal voluntary isometric contraction (MVC), rate of isometric force development (RFD) and peak power. Changes in anabolic signaling were also measured.

Results

Muscle growth

After 10 weeks of training, the quadriceps muscle volume (indicating muscle growth) increased significantly in all groups. The increase in the 30%-3 and 80%-3 condition was similar, and about twice as large as the increase seen in the 80%-1 condition.

Type I and type II muscle fiber area increased with all training conditions, with no significant between group differences.

Muscle function

After the training period, all conditions significantly increased 1RM strength. However, the increase in 1RM strength was greater in the 80%-1 and 80%-3 conditions compared to the 30%-3 condition.

MVC (maximal voluntary isometric contraction) force, knee extension maximal power output and RFD (rate of isometric force development) increased in all conditions with no between condition differences. The total work that could be completed at 30% of the subject’s 1RM also increased, with no differences between conditions.

The total work that could be completed at 80% of the subject’s 1RM increased in all groups. The magnitude of the increase was significantly less in the 30%-3 condition compared to the other conditions.

The number of repetitions that could be performed with 80% of current 1RM increased in all groups, with no between condition differences in the magnitude of the increase:

Pre-training

30%-3: 10 reps

80%-1: 10 reps

80%-3: 11 reps

Post-training

30%-3: 12 reps

80%-1: 13 reps

80%-3: 12 reps

Not surprisingly, muscle endurance (indicated by the number of repetitions that could be performed with 30% of 1RM) increased only in the 30%-3 condition.

It was also found that anabolic signaling (p70S6K activation) was activated 1 hour post-workout in the 80%-3 and 80%-1 conditions, but not in the 30%-3. However, the previous single workout study showed that the 30%-3 did activate anabolic signaling 4 hour post-workout (no 4 hour measurement was done in this training study).

Conclusions

So what’s the take home from this groundbreaking study and its predecessor?

First, it refutes the traditional recommendation that heavier loading, in the range of 6-11 reps to failure is the optimal (and only!) way to maximize muscle hypertrophy 3, 4. In a heavily cited study, eight weeks of training in a 20-28 repetition range did not elicit muscle growth despite increases in the number of repetitions that could be completed with 60% of 1RM 4. However, in a subsequent study which employed the same training method, equivalent muscle growth was found in high and low load training groups 5. It is often claimed 3, 4 that high training loads are necessary to induce muscle growth because they cause full muscle fiber recruitment and activation of type II muscle fibers, which have potential to increase in size more than type I muscle fibers 6. However, this statement is only accurate during a single repetition, since the well known size principle of motor unit activation states that motor units are recruited in an orderly fashion from smallest to largest with increasing requirement for force generation 7, 8. Thus, it is true that one single contraction performed at 30% 1RM will recruit less muscle than a single contraction preformed at 80% of 1RM. However, when a sub-maximal contraction is sustained, motor units that were initially recruited will fatigue (produce less force) or cease firing completely, necessitating the recruitment of additional motor units to sustain force generation 9. In this way, as repetitions at lighter loads are repeated to failure, near maximal motor unit recruitment will be achieved 10. Thus, lighter loads lifted to the point of failure would result in a similar amount of muscle fiber activation as compared to heavier loads lifted to failure 7, 11.

Second, although training load did not impact the magnitude of the hypertrophic response (nor maximal voluntary contraction strength, maximal instantaneous power output, and rate of force development), it did have a clear impact on max strength gains. Both the 80%-1 and 80%-3 conditions resulted in a larger increase in 1RM strength compared to the 30%-3. Thus, training with heavy loads (and lower reps) is still necessary to maximize gains in 1RM strength, because strength gains are due not only to muscle growth but also neural adaptations that are only induced by heavy lifting 12. This is important to remember if you are a power or weight lifter, but not directly relevant for bodybuilders or folks who lift weights with the goal to gain muscle.

Finally, it shows that heavy and light relative loads lifted until the point of failure result in a different time course of anabolic signaling, with p70S6K activation occurring later after exercise with light compared to heavy relative loads. It is possible that a training program that elicits increases in anabolic signaling at different time points, might induce a larger muscle growth response than a training program that constantly activate anabolic signaling either early or late post-workout. There are also many other anabolic signaling pathways that are possibly responsive to different weight lifting loads 5. How different training program manipulations affect these molecular level anabolic mechanisms is unknown and certainly warrants further study.

So bottom line; if you are looking to build muscle, don’t get stuck in the 6-10 rep range. Break out of your ego’s comfort zone. Just because you’re lifting lighter doesn’t mean you are “weaker”. So my advice is to spice your traditional 6-10 or 6-12 rep ranges with pump and burn sensation inducing higher rep ranges. In addition to avoiding injuries (which is common with constant heavy lifting), training with strict form in rep ranges in the range 20-30 to failure will nicely shock your muscles and make for a nice workout variety. And as we all know, workout variety and training periodization is essential for performance progress and continued muscle growth 13, 14.

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