Does resistance-based exercise dose matter in a patient’s pain experience?

by Jared Bauer – OMPT Fellow-in-Training

When you think of a traditional outpatient orthopedic physical therapy clinic, what do you think of? What does it look like? Exercise balls placed on wooden shelves? Thera-bands wrapped around posts? Bright colored small dumbbells neatly placed on a rack?

Although most of these pieces of equipment are still around, if you walk into an outpatient clinic today, you are most likely seeing a few new additions. Insert barbells, bumper plates and heavy dumbbells.

One reason this shift has occurred is because of the contemporary guidelines on resistance-based exercise dosage. (1,3) Specific exercise parameters (i.e. reps, sets, load, rest periods, etc.) are recommended to achieve a precise training adaptation. These training adaptations typically include strength, muscle hypertrophy and local muscular endurance.

Orthopedic manual physical therapists (OMPTs) pride themselves on precise dosing of both manual techniques along with exercise therapies to achieve improved outcomes with greater efficiency. In fact, the updated definition of orthopedic manual physical therapy now includes exercise dose as a key element of its practice. (14) This has led to a proliferation of precise dosing parameters for resistance-based exercise in our field.

However, has this new focus on resistance-based exercise prescription driven better patient outcomes?

Let’s start from the top. Is resistance-based exercise more effective than other treatments in common musculoskeletal conditions for reduction of pain, improved function, etc.? Currently for common conditions like neck, low back, and shoulder pain, this doesn’t seem to be the case. (4,8,10,11) In fact, many different treatments, including resistance-based exercise, but also yoga, Pilates, motor control exercise, and flexibility training tend to deliver similar outcomes. Of course, these are broad categories of conditions and therefore it can be argued that more narrow classifications (i.e. low back pain with movement coordination impairments) may benefit more from a specific style of exercise therapy. However, a 2022 systematic review and meta-analysis found that there is insufficient evidence supporting classifications over generalized interventions when managing LBP, potentially due to the biomechanical heterogeneity we try to place on individuals with this pain condition. (15)

Similarly, another common criticism for why resistance-based exercise has not been shown to be more effective is that it is not optimally dosed. However, is there consensus on what optimal dosage is? And furthermore, does it warrant strict adherence?

Let’s first look at how the variables of repetitions and load are interrelated. These tend to be the most common variables that we think of when prescribing exercise. They are usually prescribed along what is known as the “repetition continuum.” (13) It is as follows (13):

1. A low repetition scheme with heavy loads (from 1 to 5 repetitions per set with 80% to 100% of 1-repetition maximum (1RM)) optimizes strength increases.
2. A moderate repetition scheme with moderate loads (from 8 to 12 repetitions per set with 60% to 80% of 1RM) optimizes hypertrophic gains.
3. A high repetition scheme with light loads (15+ repetitions per set with loads below 60% of 1RM) optimizes local muscular endurance improvements.

These recommendations seem self-explanatory, right? You won’t see any powerlifters consistently training their deadlift at 135# for sets of 50 to try to gain a few pounds on their 600# 1RM. However, Brad Schoenfeld and colleagues re-examined this continuum. Here are the highlights (13):

1. High loads and low reps can be effective at increasing strength, but only in that specific movement. There is no evidence to support that this is transferrable to a neutral modality. For example, working in the ‘strength zone’ of the repetition continuum on a leg press will make you strong at a leg press, but not necessarily make you strong in a step up.
2. Hypertrophy can occur in any rep range when the load is greater than or equal to 30% of a repetition maximum. There is no ‘hypertrophy zone’. But for efficiency, moderate loads and moderate reps may be the best.
3. There is no evidence to support that local muscular endurance is affected by weighted exercise.

Mcleod et al. took this a step further and assessed other remaining variables for both strength and hypertrophy in an umbrella review that synthesized the findings from systematic reviews on the subject. (5)These variables included load, contraction type, time under tension, set end point (momentary muscular failure), volume (number of sets), set configuration, inter-set rest, periodization, weekly frequency, muscle action type, time of day and exercise order. (5) They found only a few important variables. For strength, the load (higher loads), exercise order (strength exercise first), weekly frequency (multiple times a week), and volume (multiple sets instead of 1) to be important. (5) For hypertrophy, they found only volume (multiple sets) and eccentric muscle contractions to be better  (5)These findings suggest that adherence to the strict guidelines may not be warranted.

With this much variability for healthy adults, how are OMPT’s able to translate this to the painful population? While insufficient strength or muscle hypertrophy can significantly contribute to a person’s pain experience, many other factors may also be involved, including lifestyle, psychological and social influences, cultural background, medical history, sensory processing, comorbid health conditions, genetics, sex, and life stage  (2) Furthermore, aside from the local tissue adaptation, resistance-based exercise also causes a profound systemic effect to the nervous, endocrine, immune and cardiovascular systems. (3) These systemic effects can also have positive effects on a patient’s pain experience. (12) Therefore, prescribing exercise parameters based off strength and/or muscle hypertrophy adaptations may be minimizing the pain experience and over-simplifying a complex problem.

Nevertheless, there have been a few systematic reviews that have tried to determine an optimal dosage for musculoskeletal pain conditions through resistance-based exercise. Two systematic reviews showed positive outcomes for specific dosages, one in tendinopathies and one for hip osteoarthritis (OA). In tendinopathies, Pavlova et al. found that having rest days during the week and doing heavier loads was beneficial. (9) In hip OA, Moseng et al. found a clinically significant effect of improvement in pain and to a smaller degree physical function for American College of Sport’s Medicine (ACSM) adherent exercise dosing vs uncertain dosage. (7) This was not solely related to resistance-based exercise as they included flexibility and cardiorespiratory training. It is worth mentioning that there were a number of studies that did not document their dosages well enough to be classified as either being adherent or not. The authors reported that they tried to make up for this by giving them half-credit, however, this could potentially skew the results and may lead to uncertainty in regards to the findings. Finally, there are some reviews for knee OA exercise dosage, but both of these were unable to conclude that one dosage was better than another. (6,16) 

Although these are across different conditions, it seems that an optimal resistance-based exercise dose at the individual parameter level still eludes us for pain conditions. This can be, in part, because the optimal dose even for healthy individuals has not been elucidated. But also, the complex interplay of multiple systems and past experiences in a patient’s pain offer a different set of challenges. This may require recommendations entirely different from the ones related to strength, hypertrophy, etc. Liang et al. were able to map out metabolic equivalents (METs) for a number of different exercise modalities for those with chronic low back pain and determined an ideal range for maximum amount of pain relief.⁴ This method was void of the granular discussion of specific resistance-based exercise parameters, but instead focused on total energy expenditure. This may provide a glimpse into a new focus of exercise dosage in patients with pain.

Jared Powell and colleagues effectively summarized the use of resistance-based exercise for shoulder pain, which I believe could also apply to other musculoskeletal pain conditions given the current state of the literature. They write, “Shared decision making is considered appropriate when there is not one clearly superior treatment approach available. This applies to both selection of a treatment, such as exercise, and also to the delivery of a chosen treatment, such as the exercise parameters…A useful heuristic to help guide exercise‐based rehabilitation for clinicians is that specificity of exercise type, intensity, volume, and contraction type seems to matter little for reducing the experience of shoulder pain but might matter more for enhancing shoulder function and performance.”(10) 

Despite these uncertainties, I believe OMPT’s are adequately trained with the tools to still achieve effective exercise dosing. Being rooted in an advanced clinical reasoning model that requires constant reassessment of specific functional and objective impairments allows for the flexibility of thought and practice to precisely tailor treatments to ensure agreed upon goals. Therefore, even though the boundaries of resistance-based exercise are wide and ill-defined in large scale studies, the OMPT has a framework that can allow for appropriately dosed resistance-based exercise therapy on the individual patient level.

References:

1. American College of Sports Medicine. American College of Sports Medicine position stand. Progression models in resistance training for healthy adults. Med Sci Sports Exerc. 2009;41(3):687-708. doi:10.1249/MSS.0b013e3181915670
2. Caneiro JP, Smith A, Bunzli S, Linton S, Moseley GL, O’Sullivan P. From Fear to Safety: A Roadmap to Recovery From Musculoskeletal Pain. Phys Ther. 2022;102(2):1-12. doi:10.1093/ptj/pzab271
3. Haff GG, Triplett NT. Essentials of Strength and Conditioning. 4^th Human Kinetics; 2015.
4. Liang Z, Tian S, Wang C, et al. The Best Exercise Modality and Dose for Reducing Pain in Adults With Low Back Pain: A Systematic Review With Model-Based Bayesian Network Meta-analysis. J Orthop Sports Phys Ther. 2024;54(5):315-327. doi:10.2519/jospt.2024.12153
5. Mcleod JC, Currier BS, Lowisz C V., Phillips SM. The influence of resistance exercise training prescription variables on skeletal muscle mass, strength, and physical function in healthy adults: An umbrella review. J Sport Heal Sci. 2024;13(1):47-60. doi:10.1016/j.jshs.2023.06.005
6. Messier SP, Mihalko SL, Beavers DP, et al. Effect of high-intensity strength training on knee pain and knee joint compressive forces among adults with knee osteoarthritis: The START randomized clinical trial. JAMA – J Am Med Assoc. 2021;325(7):646-657. doi:10.1001/jama.2021.0411
7. Moseng T, Dagfinrud H, Smedslund G, Østerås N. The importance of dose in land-based supervised exercise for people with hip osteoarthritis. A systematic review and meta-analysis. Osteoarthr Cartil. 2017;25(10):1563-1576. doi:10.1016/j.joca.2017.06.004
8. Mueller J, Weinig J, Niederer D, Tenberg S, Mueller S. Resistance, Motor Control, and Mindfulness-Based Exercises Are Effective for Treating Chronic Nonspecific Neck Pain: A Systematic Review With Meta-Analysis and Dose-Response Meta-Regression. J Orthop Sport Phys Ther. 2023;53(8):420-459. doi:10.2519/jospt.2023.11820
9. Pavlova AV, Shim JSC, Moss R, et al. Effect of resistance exercise dose components for tendinopathy management: A systematic review with meta-analysis. Br J Sports Med. 2023;57(20):1327-1334. doi:10.1136/bjsports-2022-105754
10. Powell JK, Lewis J, Schram B, Hing W. Is exercise therapy the right treatment for rotator cuff-related shoulder pain? Uncertainties, theory, and practice. Musculoskeletal Care. 2024;22(2):1-12. doi:10.1002/msc.1879
11. Rasmussen-Barr E, Halvorsen M, Bohman T, et al. Summarizing the effects of different exercise types in chronic neck pain – a systematic review and meta-analysis of systematic reviews. BMC Musculoskelet Disord. 2023;24(1):806. doi:10.1186/s12891-023-06930-9
12. Rice D, Nijs J, Kosek E, et al. Exercise-Induced Hypoalgesia in Pain-Free and Chronic Pain Populations: State of the Art and Future Directions. 2019;20(11). doi:10.1016/j.jpain.2019.03.005
13. Schoenfeld BJ, Grgic J, Van Every DW, Plotkin DL. Loading Recommendations for Muscle Strength, Hypertrophy, and Local Endurance: A Re-Examination of the Repetition Continuum. Sports. 2021;9(2):1-25.
14. Silvernail JL, Deyle GD, Jensen GM, et al. Orthopaedic Manual Physical Therapy: A Modern Definition and Description. Phys Ther. 2024;104(6). doi:10.1093/ptj/pzae036
15. Tagliaferri SD, Mitchell UH, Saueressig T, Owen PJ, Miller CT, Belavy DL. Classification Approaches for Treating Low Back Pain Have Small Effects That Are Not Clinically Meaningful: A Systematic Review With Meta-analysis. J Orthop Sport Phys Ther. 2022;52(2):67-84. doi:10.2519/jospt.2022.10761
16. Torstensen TA, Østerås H, LoMartire R, Rugelbak GM, Grooten WJA, Äng BO. High- Versus Low-Dose Exercise Therapy for Knee Osteoarthritis. Ann Intern Med. 2023;176(2):154-165. doi:10.7326/M22-2348