Most strength and conditioning professionals believe that training with heavier relative loads leads to improved strength gains in comparison with lighter relative loads. But how good is the evidence for this contention? Does training with heavier relative loads in fact lead to greater strength gains than training with lighter relative loads? Here is a review of the literature…
What is the background?
When developing guidance for resistance-training programs, strength and conditioning coaches and sports science researchers generally refer to three different bands of relative load, typically described as heavy (1 – 5RM), moderate (6 – 15RM) and light (15RM+, which corresponds with <65% of 1RM).
While the division between heavy and moderate relative loads is somewhat arbitrary, it is thought that the division between moderate and light loads represents a fundamental dividing line. Previous researchers and coaches have generally assumed that training with light loads of <65% of 1RM is less effective for both strength and hypertrophy gains than training with heavy loads, even in beginners.
When I reviewed the literature comparing heavy and light loads for the purposes of hypertrophy in a previous blog post, it was interesting to see the studies were not conclusive. It was not clear that heavier relative loads were any different in their ability to produce hypertrophy.
However, as we will see in this review, the evidence for heavy loads (here defined as heavier than 15RM) being superior for strength gains in comparison with lighter loads (here defined as lighter than 15RM) is actually much stronger.
Do heavy loads lead to greater strength gains than light loads?
The following studies have assessed the differences in strength gains resulting from using heavy (1 – 5RM) vs. light (15RM+) loads in untrained populations. To my knowledge, no studies have been performed in trained populations.
Campos (2002) – the researchers recruited 32 untrained males for an 8-week resistance-training program and allocated them into a low-rep group (3 – 5RM for 4 sets of each exercise with 3 minutes of rest between sets and exercises), an intermediate-rep group (9 – 11RM for 3 sets with 2 minutes of rest), a high-rep group (20 – 28RM for 2 sets with 1 minutes rest), and a control group. The subjects performed the leg press, squat, and knee extension 2 days per week for the first 4 weeks and 3 days per week for the second 4 weeks. The researchers found significant increases in 1RM strength for all three exercises in all three training groups. These strength gains were significantly greater in the low-rep group compared to the high-rep group.
Holm (2008) – the researchers recruited 11 sedentary males for a 12-week intervention in which each subject trained 3 times per week, with one leg at 70% of 1RM (heavy load) and the other leg at 15.5% of 1RM (light load). The researchers tested 1RM knee extension, isokinetic and isometric strength For 1RM knee extension, the researchers found that the strength gain was significantly higher following the heavy load condition (36 ± 5%) than following the light load condition (19 ± 2%). Similarly, the researchers found that the heavy load condition improved concentric isokinetic strength by 13 ± 5%, eccentric isokinetic strength by 18 ± 5% and isometric strength by 15 ± 4% but the light load condition did not change any of these measures significantly.
Van Roie (2013) – the researchers compared the effects of high- and low-load resistance-training on muscle volume in 56 older adults performing an intervention of 12 weeks of leg press and leg extension training at either high (2 × 10 – 15 reps at 80% of 1RM, low (1 × 80 – 100 reps at 20% of 1RM), or low+ (1 × 60 reps at 20% of 1RM followed by 1 × 10 – 20 reps at 40% of 1RM) relative loads. The researchers reported that each of the training groups significantly increase both leg press and leg extension 1RM post-intervention. For the leg press, the high and low+ groups increased significantly more than the low group (46.2 ± 32.3% and 39.2 ± 20.7% vs. 23.1 ± 20.7%). For the knee extension, the high and low+ groups increased significantly more than the low group (30.0 ± 11.5% and 29.7 ± 19.8% vs. 19.2 ± 5.3%).
Tanimoto (2008) – the researchers recruited 36 healthy but untrained young males who performed whole-body resistance training 2 times per week for 13 weeks using 3 sets each of the squat, chest press, lat-pull-down, abdominal bend, and back extension. The subjects were allocated into 3 groups: light-slow (55 – 60% of 1RM with 3-second eccentric and concentric actions), heavy (80 – 90% of 1RM with 1-second concentric and eccentric actions and a 1-second pause) and a control. The researchers observed no significant differences between the groups in respect of 1RM strength. However, there was a non-significant trend for the light-slow group to increase to a lesser extent than the heavy group (33.0 ± 8.8% vs. 41.2 ± 7.8%). Also, the increase in 1RM strength for the back extension exercise was significantly greater in the heavy group than in the light-slow group.
Tanimoto (2006) – the researchers recruited 24 healthy but untrained young males who performed whole-body resistance training 3 times per week for 12 weeks with 3 sets of knee extension exercise. The subjects were allocated into 3 groups: light-slow (50% of 1RM with 3-second eccentric and concentric actions), light-normal (50% of 1RM with 1-second eccentric and concentric actions and a 1-second pause), and heavy (80% of 1RM with 1-second concentric and eccentric actions and a 1-second pause). The researchers measured 1RM knee extension, isometric and isokinetic strength at 90, 200 and 300 degrees/s. There were no significant differences between isokinetic or 1RM strength gains between the groups. However, the heavy-load group increased isometric strength by significantly more than the light groups.
Mitchell (2012) – the researchers recruited 18 healthy but untrained young males for a 10-week study in which they performed single-leg resistance-training 3 times per week. The researchers randomly allocated each of the subjects’ legs to 1 of 3 different training protocols that differed by volume and by relative load, as follows: 30% of 1RM x 3 sets, 80% of 1RM x 1 set, and 80% of 1RM x 3 sets. The researchers found that all training protocols led to significant increases in 1RM but the increase in 1RM was greater in the 80% of 1RM x 1 set and 80% of 1RM x 3 set conditions than in the 30% of 1RM x 3 sets condition. The researchers also reported that isometric strength increased in all conditions but there were no significant differences between conditions.
Ogasawara (2013) – the researchers recruited 9 young, untrained males for a 6-week, high-load-resistance-training program for the bench press using 75% of 1RM for 3 sets, 3 times per week, followed by a 12-month detraining period, followed by a 6-week, low-load-resistance-training program using 30% of 1RM for 4 sets, 3 times per week. The researchers found that post-intervention, 1RM and isometric strength both increased significantly in both groups. However, they found that the increase in the heavy-load group was significantly greater than that in the light-load group for both (1RM 21.0 ± 5.9% vs. 8.6 ± 2.9%) and isometric (13.9 ± 7.5% vs. 6.5 ± 4.9%) strength measures.
Moss (1997) – the researchers recruited 30 physical education students and randomly allocated them into 1 of 3 groups, who trained with loads of either 90%, 35%, or 15% of IRM. The groups trained using 3 – 5 sets, 3 times per week for 9 weeks. The 90% group trained using 2 reps, the 35% group using 7 reps and the 15% group using 10 reps. The researchers reported that 1RM increased by 15.2 ± 4.5%, 10.1 ± 5.9% and 6.6% in each of the 90%, 35% and 15% groups, respectively. The researchers found that the increase in the 90% group was significantly greater than the increase in the 15% group.
Anderson (1982) – the researchers assessed the effects on strength gains of 3 different resistance training programs: high resistance-low repetition, medium resistance-medium repetition, and low resistance-high repetition. The researchers found that the high resistance-low repetition training condition led to significantly greater strength gains than the other two conditions.
Aagaard (1996) – the researchers compared the effects of strength training using high loads and slow speeds (4 sets of 8 reps with 8RM loading) and low loads and high speeds (4 sets of 24 reps with 24RM loading) in 22 elite soccer players. Before and after the trial, the researchers tested isokinetic concentric and eccentric knee extension and flexion torques at 30, 120, 240 degrees/s. The researchers found that isokinetic knee strength did not increase significantly in the low load group. On the other hand, concentric torque increased significantly in the high load group for both knee extension and flexion at 30 degrees/s and eccentric torque increased significantly at 30, 120 and 240 degrees/s.
Weiss (1999) – the researchers compared the effects of three resistance-training protocols with either high, moderate or low loads in 38 untrained males. The subjects trained 3 times per week for 7 weeks with 4 sets of squats using a 3 – 5RM, 13 – 15RM, or 23 – 25RM load, respectively. The researchers found that squat strength and knee extension peak torque at 60 degrees/s significantly increased in all groups. However, squat strength improved significantly more in the high-load group than in the low-load group.
Bemben (2000) – the researchers compared the effects of two volume-matched, high-load (80% of 1RM) and low-load (40% of 1RM) resistance-training protocols on strength gains in 25 early postmenopausal, estrogen-deficient women. The protocols were performed for 3 sets, 3 days per week for 6 months. The researchers found that while both training groups displayed similar increases measures of lower body strength and hip strength, the high-load group displayed significantly greater improvements in upper body strength (25% vs. 16%).
Rana (2008) – the researchers assessed the effects of relative load on strength gains in 34 healthy adult females who performed a 6-week resistance-training program comprising the leg press, back squat and knee extension. The researchers allocated the subjects into various different groups, including a control, a traditional strength (heavy) group, a traditional endurance (light) group, and a slow-velocity group. The heavy group trained at 6 – 10 RM, the light group trained at 20 – 30RM, both with 1 – 2 second concentric and eccentric phases, and the slow-velocity group trained using a 6 – 10RM with a 10-second concentric and 4-second eccentric phase. Comparing just the traditional strength and traditional endurance groups, the researchers found that the traditional strength group displayed significantly greater 1RM strength gains in the leg press and knee extension exercises than the endurance group. The traditional strength group also showed a non-significant trend to display greater increases in strength for the squat.
Popov (2006) – the researchers recruited 18 young, physically active males for an 8-week intervention, in which they trained their leg extensor muscles 3 times per week using the leg press exercise. A heavy group worked at 80% of MVC and a light group worked at 50% of MVC. The researchers reported that strength increased significantly in both the heavy and light groups. While there was a non-significant trend for the heavy group to increase strength (measured as maximum force developed during the leg press exercise) to a greater extent (35% vs. 21%), there was no significant difference between the groups.
Hisaeda (1996) – the researchers compared the effects of two resistance-training protocols using the knee extension exercise in 11 untrained female subjects. In a light-load protocol, the subjects used 4 – 5 sets of 15 – 20RM with sufficient inter-set rest periods. In a heavy-load protocol, the subjects used 8 – 9 sets of 4 – 6RM with a 90-second inter-set rest period. Before and after the intervention, the researchers measured isokinetic knee extension torque at 0, 60, 180, and 300 degrees/s. The researchers found that isokinetic torque increased significantly in both groups but there was a non-significant trend for the light-load protocol to lead to greater strength gains (43.4 ± 47.5% vs. 27.4 ± 31.3%).
Stone (1994) – the researchers compared the effects of three resistance-training protocols with either high, moderate and low loads in 50 untrained females. The protocols involved 9 weeks of training either involving 3 sets of 6 – 8RM, 2 sets of 15 – 20RM, or 1 set of 30 – 40RM, respectively. The researchers found that in all groups there were significant strength gains as measured by 1RM but there were no significant differences between groups. There was a non-significant trend for the high-load group to display the greatest gains in strength.
Leger (2006) – the researchers recruited 25 healthy but untrained males for an 8-week intervention of resistance training followed by de-training. The subjects were allocated into one of two training groups (low reps or high reps) that were matched for age, height, weight, VO2-max and muscular strength and endurance. The subjects performed the same training protocol as described in Campos (2002) above. The researchers found that resistance training led to 50% and 15% strength gains in the leg extension and squat, respectively, but there was no strength gain for the leg press exercise. The researchers found no significant differences in strength gains between the two groups and did not provide data for the two groups separately. Therefore, it was not possible to ascertain whether there was any non-significant trend.
Pruitt (1995) – the researchers compared the effects of two resistance-training protocols with either high or low loads in 26 older females (65 – 82 years). The high-load group performed 7 repetitions at 80% of 1RM and the low-load group performed 14 repetitions at 40% of 1RM) for 3 sets each in 10 exercises, 3 times per week for 1 year. The researchers found that arm strength increased significantly more in the low-load group than in the high-load group (65.5% vs. 27.4%). However, both high- and low-load groups displayed significant increases in 1RM for chest (10.1% vs. 15.4 %), shoulders (18.5% vs. 27.4 %), upper back (41.4% vs. 21.0 %), lower back (35.8% vs. 35.4 %), hips (50.9% vs. 66.4 %), and legs (47.6% vs. 42.4%) with no significant differences between these increases.
How can we summarize the results of these studies?
The following table sets out the results of the preceding studies. It shows that in 13 out of the 18 studies presented above, there was a significantly superior strength gain in the heavier load condition in comparison with the lighter load condition. In 3 further studies, there were no significant differences between conditions albeit there was a non-significant trend in favour of a bigger strength gain in the heavier load condition in comparison with the lighter load condition. In 1 further study, there was no significant difference between conditions and no data were presented to allow the determination of non-significant trends. In 1 final study, the lighter load condition achieved greater strength gains than the higher load condition.
In conclusion, it seems clear that while training with both heavy and light loads can lead to strength gains, training with heavier loads (here defined as heavier than 15RM) leads to superior strength gains than training with lighter loads (here defined as lighter than 15RM).
What are the practical implications?
For personal trainers
When working with untrained individuals, personal trainers can be assured that some strength gains will occur even with very light loads.
For maximizing strength gains in untrained individuals, personal trainers should be aware that using heavier loads than 15RM is optimal.
For strength athletes
For maximizing strength gains, strength athletes should make use of loads that are heavier than 15RM.