Moving at the Speed of Strength: How Long to Get Strong?

Strength is a skill that you train and can gain faster than you think.

Posted Mar 11, 2020

To get stronger you have to first be weakened. It's a stimulus response adaptation and one of the many apparent paradoxes in human physiology — or in being human, generally.

When we hear the word "strength" an image of muscle pops into most minds. And that last bit is important because it's in the brain and spinal cord where the initial changes in strength occur. That's because strength should best be considered a skill and, as such, relies on refinement in the nervous system to be expressed.

A paradigm used commonly in research to study strength and adaptations to training is single-limb resistance training. This improves strength not only in the limb that is actively trained but also in similar muscles of the untrained limb due to neuroplastic strengthening of connections within the brain and spinal cord.

Increased strength of the untrained limb after was called 'cross-education' when first discovered by Edward Scripture over 100 years ago and is still commonly referred as such. It's interesting to point out that this study, which spawned a research tradition resonating to present day, was based on the results obtained from two participants, both women. We owe a great debt to Miss Brown and Miss Smith. It's incredibly ironic that such an influential endeavor laid the bedrock for future studies most of which have massively underrepresented (or truly ignored) women. That is changing but the changes needs to increase and continue.

Cross education training improves strength on the more affected side after stroke. To be really useful in a clinical setting, understanding about the effective dose of training, including both how often and for how many weeks training should be performed, is key. But this kind of information is difficult to extract from the scientific literature where so many different protocols have been used.

For application to rehabilitation, a really important part of dosing is how often is training required? Looking at historical literature, is the dose as low as what Scripture used in 1894—9 consecutive days—or should we look back to the extraordinary work of Gustav Fechner (1801-1887) in 1857? Fechner performed one of the first studies documenting how practice could increase strength by lifting 2 dumbbells (~9 lbs) in each hand up over his head as many times as he could every day for 60 days. He improved from 104 repetitions initially to 692 on day 55.

We've been interested for a while in how to help people who've been injured improve strength and function. Trevor Barss, Taryn Klarner, Greg Pearcey, Yao Sun and myself decided to try and figure out the minimum number of training sessions required to improve strength. We used both a traditional protocol found in many studies (3 sessions per week for 6 weeks) as well as a protocol inspired by Scripture and Fechner of daily training for 18 consecutive days.

Some cool things were discovered. Training every day for 18 days produced the same strength gains in the untrained limb as 6 weeks of traditional training. But, and this only increased our respect for Gustav Fechner's fortitude, the lack of rest days made it very uncomfortable. Basically significant gains in strength in the untrained limb could be done with either 4 weeks (12 sessions) of ‘traditional’ training or 15 days of ‘daily’ training. Excitingly for application to rehabilitation, while the increases in untrained limb strength were similar between the ‘daily’ (7.8%) and ‘traditional’ (12.5%) training protocols, increases with ‘daily’ training took half the number of weeks.

With a ‘traditional’ training paradigm, untrained limb strength peaked after 5 weeks of training and did not increase further while with ‘daily’ training, no plateau in strength occurred after 18 consecutive days, indicating that perhaps more than 18 sessions are required to optimize the contralateral increases in strength. Fechner would likely have been very interested in this!

The takeaway is that when incorporating a ‘traditional’ training paradigm, 5 weeks of unilateral training is likely to be optimal for inducing untrained arm strength gains prior to a plateau. If the focus of recovery is an impaired or immobilized limb such as occurs after stroke, the aim is to optimize improvements in strength and function of the more affected limb in the minimal amount of time to allow rapid progression to other rehabilitation activities. Since a similar increase in strength can be achieved in dramatically less time, minimizing rest days during training may improve the efficiency of single arm training when improvement in the untrained limb is the focus.

A critical point is that all training is training the brain. And certain kinds of training can be uncomfortable and rely deeply on determination to push through physical discomfort. Whether such endurance and fortitude is necessary or reasonable depends, like many things in life, entirely on the situation and application. But we now know that the speed of strength—should we be willing to push very hard—moves much faster than we thought.

(c) E. Paul Zehr (2020)

NOTE: This post was written in collaboration with Dr. Trevor Barss. Trevor is currently a Post-Doctoral Fellow within the Neuroscience and Mental Health Institute and Faculty of Medicine and Dentistry at the University of Alberta. His research interests lie in exploring changes in the neuromuscular system associated with voluntary and electrically evoked muscle contractions to facilitate improved rehabilitation after damage to the nervous system.