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Muscle Building: Optimum Training Intensity

Strength Training Intensity and Muscle Building (Hypertrophy)

A common, and fairly universal recommendation, for a resistance training intensity to provide the optimal stimulus for muscle hypertrophy (muscle growth) is to perform resistance training at an intensity of 70-90% of 1 repetition maximum (RM) – this would typically involve performing between 4 and 12 repetitions at (equivalent to training between 90 and 70% of 1 RM) . In fact the ACSM (American College of Sports Medicine) position stand (ACSM 2009) is that novices train at an intensity that correspond with approximately 70-80% of 1RM (8-12 repetitions), whilst individuals with 6months, or more, resistance training experience should use a range of 70-100% of 1RM (1-12 repetitions) with greater emphasis placed on training at 85-100% of 1RM (1-6 repetitions). A quick look through popular bodybuilding websites and forums will see similar recommendations, with the typical recommendation being to train in the range of 4-8RM. However, there is a large amount of research that supports the use of training at lower intensities, in addition to the higher intensity training, provided that the lower intensity training is performed to failure. In addition it is important to consider individual differences in muscle fibre make-up (i.e. percentage of slow twitch and fast twitch muscle fibres) as well as differences in muscle fibre make-up between muscle groups (e.g. the soleus has over 80% Slow twitch fibres whereas triceps typically have less than 35% slow-twitch fibres) when considering the correct repetition ranges – this is something we will look at in a later article. 

What research says about training intensity and Muscle Hypertrophy

Despite the current popularity of training between 4-12RM for muscle hypertrophy there are a number of studies that demonstrate that that significant muscle fibre hypertrophy may occur through low intensity resistance training (Alway et al., 1990; Burd et al., 2010; Burd et al., 2012; Mitchell et al., 2012; Wilbourn et al., 2009). Researchers (Wilbourn et al., 2009) have demonstrated that both moderate-intensity training (4 sets of 18-20 reps at 60-65% 1RM) and high intensity training (4 sets of 8-10 repetitions at 85% 1RM) led to significant increases in key markers of muscle hypertrophy stimulation as well as decreasing levels of myostatin (a protein that inhibits muscle growth) and Cyclin-dependent kinase inhibitor 1B (a cell cycle inhibitor that stops/slows down the cell division cycle). This is supported by research showing that myofibrillar protein synthesis reaches maximum stimulation at around 60% 1RM (~20RM) with no further increases occurring at higher intensities (Kumar et al., 2009). Recent research has also demonstrated that 18-20reps at 60-65% 1RM was equally effective as 8-10reps at 80-85% 1RM for upregulation of a key signalling pathway (ERK 1/2 signalling) that is believed to play a role in muscle hypertrophy adaptations (Taylor et al., 2012). Exercise at 65% was also found to result in a more preferential increase in Insulin-like Growth Factor 1 Receptor (IGF-1R).

Interestingly, low intensity high volume exercise (30% 1RM sets to failure) has been shown to have a potent stimulatory effect on anabolic signalling and protein synthesis (Burd et al., 2010). The researchers found that the low-intensity high volume approach appeared to be more effective at inducing muscle anabolism than high-intensity low volume resistance training (90% 1RM sets to failure). Recent research also demonstrated that low intensity resistance exercise (3 sets to failure at 30% 1RM) was found to be equal to high intensity (3 sets to failure at 80% 1RM) for muscle hypertrophy (Mitchell et al., 2012). Taken together these studies go against the idea that a high intensity is the prerequisite for maximizing muscle fibre recruitment. In fact these studies support the idea that low-moderate intensity high-volume exercise, when performed to failure, appears to be sufficient to result in full muscle fibre recruitment and is equal to high intensity resistance exercise for the stimulation of muscle protein synthesis. 

What does this mean for Muscle Building Training?

Ok, so should you ditch the high intensity training and concentrate on high-volume low-moderate intensity (LMI) training? The picture is still not completely clear but it makes sense to follow a training approach that incorporates both high intensity training and LMI training. This is supported by research that shows that a combination of training at 10RM and low intensity high-repetition training was more effective than 10RM and high intensity training for improvements in 1RM, muscular endurance, and muscle hypertrophy (Goto et al., 2004). The researchers concluded that a combination of high intensity and low-intensity training is an effective way to optimize strength gains during a periodized training program.

There are a number of advantages to incorporating LMI training along with high intensity training: Firstly, concentrating solely on high intensity training places great strain on the CNS system and greatly increases the risk of CNS fatigue/overtraining – by replacing a portion of the training volume with LMI training you reduce the overall load on the CNS system; Secondly, incorporating LMI training greatly increases the total work volume - a key stimulus to muscle development; Thirdly, low-moderate intensity high volume training will help to ensure that you fully target slow twitch muscle fibres as well as the fast twitch muscle fibres. 

How can it be incorporated into training?

The first consideration is - at what point in your workout should you incorporate LMI training into your existing workout? The ACSM recommendations are to perform higher intensity exercises first followed by lower intensity exercises. This approach has a number of key advantages firstly it allows you to maximize your high intensity training at the start of the workout (important since fast twitch fibres are the first to fatigue) and it ensures that the slow twitch fibres are progressively fatigued throughout the workout. The second consideration is - what percentage should high intensity training and LMI training should you include? The answer to this is not completely clear although it makes sense to have a fairly even split between intensities. 

An approach I have used for the last two years with good results, for a natural hardgainer, is to split the training into three intensity ranges with each comprising approximately 1/3 of the workout (in terms of sets) e.g.

1/3 of the workout in the 2-6 rep range
1/3 of the workout in the 8-12 rep range
1/3 of the workout in the 15-25 rep range

An example 9 set workout (in terms of RM) would be:

Set 1: 2RM (95% 1RM) = 190 (Total Weight lifted in set based on 1RM of 100kg)
Set 2: 4RM (90% 1RM) = 360
Set 3: 6RM (85% 1RM) = 510
Set 4: 8RM (80% 1RM) = 640
Set 5: 10RM (75% 1RM) = 750
Set 6: 12RM (70% 1RM) = 840
Set 7: 15RM (65% 1RM) = 975
Set 8: 20RM (60% 1RM) = 1200
Set 9: 25RM (55% 1RM) = 1375 


In terms of sets the workout is split evenly with 3 sets in each of the workout ranges. However, if we calculate the volume (based on a 1RM of 100kg) it increases significantly between each of the three rep ranges:

Rep Range 1 (2-6 reps): Total reps = 12, Total weight lifted = 1060
Rep range 2 (8-12 reps): Total reps = 30, Total weight lifted = 2230
Rep range (15-25 reps): Total reps = 60, Total weight lifted = 3550 


Alway SE, Sale DG, MacDougall JD. Twitch contractile adaptations are not dependent on the intensity of isometric exercise in the human triceps surae. Eur J Appl Physiol Occup Physiol. 1990;60:346–352. 

American College of Sports Medicine. (2009) American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009 Mar;41(3):687-708. 

Burd NA, West DW, Staples AW, Atherton PJ, Baker JM, Moore DR, Holwerda AM, Parise G, Rennie MJ, Baker SK, Phillips SM. (2010) Low-load high volume resistance exercise stimulates muscle protein synthesis more than high-load low volume resistance exercise in young men. PLoS One. 2010 Aug 9;5(8):e12033. 

Burd NA, Mitchell CJ, Churchward-Venne TA, Phillips SM.(2012) Bigger weights may not beget bigger muscles: evidence from acute muscle protein synthetic responses after resistance exercise.Appl Physiol Nutr Metab. 2012 Jun;37(3):551-4. Epub 2012 Apr 26.

Goto K, Nagasawa M, Yanagisawa O, Kizuka T, Ishii N, Takamatsu K. (2004) Muscular adaptations to combinations of high- and low-intensity resistance exercises. J Strength Cond Res. 2004 Nov;18(4):730-7. 

Kumar V, Selby A, Rankin D, Patel R, Atherton P, Hildebrandt W, Williams J, Smith K, Seynnes O, Hiscock N, Rennie MJ. (2009) Age-related differences in the dose-response relationship of muscle protein synthesis to resistance exercise in young and old men. J Physiol. 2009 Jan 15;587(Pt 1):211-7. Epub 2008 Nov 10. 

Mitchell CJ, Churchward-Venne TA, West DD, Burd NA, Breen L, Baker SK, Phillips SM. (2012) Resistance exercise load does not determine training-mediated hypertrophic gains in young men. J Appl Physiol. 2012 Apr 19. [Epub ahead of print] 

Taylor LW, Wilborn CD, Kreider RB, Willoughby DS. (2012) Effects of resistance exercise intensity on extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase activation in men. J Strength Cond Res. 2012 Mar;26(3):599-607. 

Wilborn CD, Taylor LW, Greenwood M, Kreider RB, Willoughby DS. (2009). Effects of different intensities of resistance exercise on regulators of myogenesis. J Strength Cond Res. 2009 Nov;23(8):2179-87.