A lot of people will say that you need to get a full range of motion (ROM) when exercising specific muscle groups but this isn’t entirely true, especially when it comes to hypertrophy or mass building.
Compound exercises, which are exercises which engage multiple muscles/groups give us more bang for our buck but the real limitation with compound exercises is that the amount of weight one can actually lift is dependent on the strength of other muscles being engaged in the lift. For example, bench presses are a compound exercise designed to target the pectorals and engage the triceps and delts. The strength of the triceps determines the weight one can lift to achieve a full range of motion. So if someone has a really strong chest but weak triceps, a bench press is going to be inefficient for its intended purpose at a reduced load to compensate for the tricep weakness.
A shorter range of motion, however, where the use of triceps in this example is eliminated, will focus the load squarely on the pectorals allowing a much heavier lift without fatiguing the triceps allowing us to build our chest and then focus on building the triceps separately so as to achieve full range of motion on the bench press with equal efficiency for all muscle groups involved in the exercise.
Compound exercises are amazing but the way we are taught to work out is often ignorant of the needs of individuals. If we were all in perfect proportions with equal amounts of strength in every muscle then that’s fantastic, stick to the status quo and start with compound exercises and end your sessions with isolated exercises.
But for the average person, if your compound exercises are inefficient because certain muscle groups are weaker than others involved in the exercise, iso exercises are the way forward for you to build strength in those muscles that are holding your compound exercises back. If your triceps are weak, tricep push downs will be an effective method to build the triceps and incline cable flies will help to isolate the shoulders and pectorals, as separate exercises, these will help build the triceps and the pectorals so that the bench press becomes a more efficient exercise later.
A similar result will be observed in a bench press which uses around 50% range of motion, so you get a half-lift without the final push from the triceps. Though it may feel silly at first, the smaller range of motion means the intended muscles are being isolated but provided you’re getting the full contraction on the muscle you’re targeting, it’s a job well done and the intended muscles will experience growth and increased strength (Schoenfeld & Grgic, 2020), there are also arguments for the reduction of fatigue resulting from excessive overload in inefficient muscles when a reduced range of motion is used.
Compound exercises are still great, especially for building strength in weaker muscles whilst maintaining strength in other muscles but strength and mass will not increase in these muscles whilst weaker muscles are holding them back. For example, with a full range of motion, you might achieve a 14kg lateral raise targeting all aspects of the delt but with a 40% range of motion targeting the medial delt, you’ll find you can lift 20kg and by doing so, you’ll gain mass in this area giving the impression of having much larger shoulders, that said it’s important not to neglect the anterior and posterior delts but these can be more effectively targeted at a great weight through exercises such as flies and rear flies as opposed to a full range of motion lateral raise.
But what happens if the inefficiency is the other way around with the primary muscles being weaker than the final muscles (eg. the chest muscles weaker than the triceps)? There is a way around this but it isn’t a common feature of most commercial gyms in the UK and that’s to add accommodating resistance to the exercise. In a bench press, this can be done by incorporating chains hung over the bar so that the weight of the chains as they’re lifted becomes heavier as they raise off the floor. This allows the pectorals to take a lighter load whilst the triceps push upwards with a heavier load allowing for continued growth and maintenance. Neely et al. (2010) found that the resistance nearly doubled at the top of a lift compared to at the bottom. The study, ‘A mechanical comparison of linear and double-looped hung supplemental heavy chain resistance to the back squat: a case study’, looked at this in detail and found the variable resistance at its peak was 78-89%, but when the weight of the chains was unloaded as a person entered the squat position, the resistance fell to around 36-42%. The difference in results was caused by how the chains were hung, whether they were doubled over or not. Certain resistance machines utilise the same principles and they’re nothing new (see the second photo on the Facebook page which can be found here, the first accommodating resistance machine was designed in 1982 by Dr Gustav Zander, image source: Medico-Mechanical Gymnastics 1896) and pre-World War One, accommodating resistance was a popular method of exercise.
Zatsiorsky & Kraemer (2010) explained in their book, ‘Science and Practice of Strength Training’ that maximum benefits were realised by maximising muscle tension throughout the entire lift and that this was most effectively achieved through accommodating resistance when inefficiencies occurred at the start of compound lifts.
References
Neelly, K.R., Terry, J.G. and Morris, M.J. (2010) “A mechanical comparison of linear and double-looped hung supplemental heavy chain resistance to the back squat: A case study,” Journal of Strength and Conditioning Research, 24(1), pp. 278–281. Available at: https://doi.org/10.1519/jsc.0b013e3181b2977a.
Schoenfeld, B.J. and Grgic, J. (2020) “Effects of range of motion on muscle development during resistance training interventions: A systematic review,” SAGE Open Medicine, 8, p. 205031212090155. Available at: https://doi.org/10.1177/2050312120901559.
Zatsiorsky, V.M. and Kraemer, W.J. (2006) Science and practice of strength training. Champaign, IL: Human Kinetics.