Volume vs Intensity in Neurological Rehabilitation: Why Consistency Often Matters More
I recently came across an interesting newsletter item from "Building the Elite" about the relative importance of training volume versus intensity. The argument—made by someone preparing candidates for special forces selection—was that volume is the primary training variable to manage. This is because it has the greatest impact on the training programme's effectiveness, while intensity determines the type of adaptation you're targeting.
This struck me as highly relevant to neurological rehabilitation. Let's see if you agree.
The Principle: Intensity Determines What; Volume Determines How Much
The core insight is this: if you change the intensity of a training session too much, you're no longer training the same physiological quality. You've changed the ingredient, not added more. For endurance athletes, raising the intensity during what was meant to be an aerobic session turns it into anaerobic work—a different training stimulus entirely. The session might still feel productive, but it's producing a different adaptation.
Volume, by contrast, accumulates. It's the variable that determines how much of a given stimulus your body receives over weeks and months. This distinction has profound implications for anyone using FES cycling or other rehabilitation technologies after spinal cord injury, stroke, or other neurological conditions. And the research increasingly supports this view.
The Evidence: Volume Drives Adaptation
The dose-response relationship in neurological rehabilitation is now well-documented. Donnellan-Fernandez, Ioakim & Hordacre (2022), reviewing the evidence on dose and intensity of stroke training, found a clear relationship between training dose and outcomes—a meta-regression of 30 studies involving 1,750 stroke survivors showed that larger doses led to clinically meaningful improvements.
Perhaps more telling is research comparing robot-assisted therapy with conventional physiotherapy. Park et al. (2025), in an umbrella review published in Stroke, found that robotic rehabilitation provides little or no additional benefit when therapy dose and intensity are matched. The technology isn't magic—it's simply an efficient delivery mechanism for repetitions. What matters is the volume of practice, not the sophistication of the equipment delivering it.
This aligns with foundational research on motor learning. Animal studies demonstrate that 400–600 repetitions per session are required to produce lasting changes in cortical representation. Human studies suggest similar magnitudes—hundreds of daily upper limb repetitions, thousands for gait—to optimise neural adaptation.
KEY POINT: The research consistently shows that cumulative training volume—not the delivery method—drives neurological adaptation. Expensive, matched-for-dose technology produces the same outcomes as conventional therapy.
How This Applies to FES Cycling
Consider FES cycling, where we can easily adjust both intensity (by changing stimulation parameters and cycling resistance) and volume (varying session duration, weekly frequency).
A common temptation is to increase resistance to pedalling to make sessions feel more challenging. Clients want to challenge their muscles to work harder, and this is understandable. But if the added load means muscles fatigue within minutes rather than sustaining activity for 30-60 minutes, you've fundamentally changed what you're training.
Low-to-moderate resistance with extended-duration training trains the cardiovascular system, builds muscular endurance, and drives metabolic adaptations—improved insulin sensitivity and better lipid profiles—that matter for long-term health. Higher resistance for shorter periods shifts toward strength training, which definitely has its place, but produces different outcomes. Ideally, we want both.
Research on spasticity in spinal cord injury clearly illustrates this volume principle. Fang et al. (2021), in a systematic review and meta-analysis examining the effect of FES cycling on spasticity in spinal cord injury, found that spasticity reduced significantly only after more than 20 training sessions. The number of sessions wasn't linearly related to improvement, which suggests that approximately 20 sessions mark a threshold below which efficacy isn't achieved.
Kuhn, Leichtfried & Schobersberger (2014), following participants for four weeks of FES cycling (two sessions per week during acute rehabilitation), found that spasticity during knee movement decreased with muscle cross-sectional area increasing. In chronic injury, Sadowsky et al. (2013) found that hamstring and quadriceps strength were 30–35% greater in the FES group, along with significantly higher quality-of-life measures.
These weren't high-intensity protocols. They were consistent, moderate-volume programmes maintained over time.
KEY POINT: When adjusting FES cycling parameters, consider whether you're trying to accumulate more aerobic training volume or change to a different type of training stimulus. They're not the same decision—and the evidence suggests volume matters more than intensity for most rehabilitation goals.
The Rehabilitation Volume Problem
For people recovering from neurological injury, volume is often the limiting factor, but not in the way athletes typically experience it.
The constraint isn't usually the willingness to train. It's typically a long list of things. It might be access to equipment, therapy time, carer support, fatigue, and the simple logistics of daily life with a disability. These realities mean that rehabilitation volume is frequently lower than optimal for adaptation.
The numbers are sobering. Donnellan-Fernandez, Ioakim & Hordacre (2022) reported that less than 8 minutes per day is directed toward upper limb rehabilitation early after stroke, during the very period when enhanced neuroplasticity may offer the greatest opportunity for recovery. Current services, however well-intentioned, often don't deliver sufficient volume to achieve maximal benefit.
This makes the volume we *can* achieve even more important to protect.
When a therapy session gets interrupted, shortened, or made more intense to "compensate" for reduced time, we may actually be diminishing its value. A 20-minute high-intensity session is not equivalent to a 45-minute moderate session—it's a different training stimulus with different outcomes.
Frequency: A Sub-Variable Worth Protecting
The original article I read made an astute observation: frequency is really a component of volume. If you're measuring weekly training time, frequency simply describes how you've divided that total. But in rehabilitation contexts, frequency has independent importance. We need to account for the carryover effects of an intervention. For example, if we use passive stretching to manage spasticity, it's valuable to know how long the benefits of stretching last. Once we know, we can think about the frequency of applying that intervention.
Research on standing illustrates this vividly. A rapid review by the Washington State Health Care Authority (2019) found that the effects of weight-bearing and standing are transient, lasting, in some studies, only until the following day. One often-cited case study found that standing produced an immediate reduction in lower extremity spasticity lasting a few hours after treatment, with a reduction in spasms lasting until the morning after.
Shields & Dudley-Javoroski (2005), in a case report monitoring standing wheelchair use, captured this from the patient's perspective. The participant believed his standing programme had a beneficial effect on his lower extremity spasticity and frequently performed standing before tasks such as dressing and showering. He stated that “on days he did no standing, his spasms were more frequent and more bothersome”. This means standing once weekly, regardless of duration, cannot maintain spasticity benefits. The volume needs to be distributed across multiple sessions—typically 30–60 minutes, five days weekly—to sustain adaptation.
The same principle applies to FES cycling, range-of-motion work, and most other rehabilitation interventions. A single long session cannot substitute for consistent, distributed practice.
KEY POINT: When life forces a choice between one longer session or two shorter ones, the distributed approach often produces better outcomes—particularly for spasticity management and cardiovascular conditioning. The transient nature of many rehabilitation effects demands frequency, not just total time.
Individual Variation: Why Standardised Protocols Miss the Mark
One important caveat: dose-response relationships aren't uniform across individuals.
Gauthier et al. (2024), examining dose response to upper extremity rehabilitation in *Stroke*, found the relationship was bimodal. Of 75 participants with sufficient data for analysis, 42% required less than 5 hours of motor practice before reaching a plateau in movement kinematics. But 55% required more than 10 hours, and 34% required more than 30 hours.
In other words, some people respond quickly to relatively modest doses, while others require substantially more practice to achieve meaningful change. Traditional "one-size-fits-all" rehabilitation programmes—the same duration and frequency for everyone—will inevitably under-dose some patients and potentially over-dose others.
This argues for individualised volume prescription based on ongoing assessment of response, rather than standardised protocols applied uniformly.
Exercise Selection Narrows Quickly
Once you know what physiological quality you're targeting, the appropriate methods become relatively clear:
Cardiovascular health → sustained aerobic activity (FES cycling, arm ergometry)
Bone density maintenance → weight-bearing (standing frames, vibration, assisted walking)
Spasticity management → prolonged stretch, weight-bearing inhibition, distributed FES cycling, electrotherapy
Muscle preservation → electrical stimulation with sufficient intensity to produce visible contractions
Motor relearning → high-repetition, task-specific practice
The choices narrow based on your goals. After that, the primary variable to manage is volume: how much of the appropriate stimulus can you accumulate consistently over weeks and months?
This is where long-term thinking matters. A rehabilitation programme that delivers moderate, sustainable volume over the years will outperform an intensive burst followed by abandonment. Huh et al. (2025), in a randomised controlled trial of community-based exercise programmes for ambulatory individuals with spinal cord injury, found that adherence rates were high when programmes were well-structured and supported, and this adherence translated to meaningful functional improvements, including enhanced aerobic capacity, lower extremity strength, and flexibility.
Practical Application
If you're managing your own rehabilitation, or supporting someone who is, here's how this principle translates. Whatever the goal or exercise programme, the most important step is adherence - the ability to “stick at it”, otherwise forget improvements.
1. Define the adaptation you're targeting. What are you actually trying to improve? Cardiovascular fitness? Spasticity? Bone health? Motor function? Each requires different methods and different volumes.
2. Set intensity at the level that produces that adaptation. For aerobic work, this means a sustainable effort you can maintain for 30–60 minutes. For strength, adequate resistance. For spasticity management through standing, sufficient duration in weight-bearing.
3. Protect volume as your primary variable. The total amount of appropriate training accumulated over time matters more than the intensity of any individual session. Twenty FES cycling sessions appear to be a threshold for spasticity benefits (Fang et al., 2021). Hundreds of repetitions daily may be needed for motor relearning.
4. Distribute volume across the week. Multiple moderate sessions typically outperform infrequent intense ones. Standing benefits are transient—daily practice maintains them; weekly practice doesn't.
5. Plan for sustainability. The programme that continues for years beats the programme that exhausts motivation in months. Palermo et al. (2022) found that structured support and weekly monitoring improved adherence substantially in home-based rehabilitation programmes.
6. Monitor your individual response. Some people plateau quickly; others need substantially more volume (Gauthier et al., 2024). Adjust based on what's actually working, not standardised protocols.
A Realistic Perspective
None of this is to say intensity doesn't matter. The stimulation parameters of an FES device must be sufficient to produce strong muscle contractions. The standing frame, or exoskeleton, ideally needs to ensure you bear your actual body weight. Sub-threshold stimulation produces no motor function adaptation.
But once intensity is set appropriately for the goal, volume becomes the variable with the most room for optimisation, and the one most often compromised by the practicalities of life with a disability.
In my experience, the people who achieve the best long-term outcomes are those who establish sustainable routines they can maintain consistently. Not the most intensive protocols, but the most persistent ones. The research supports this observation: it's accumulated practice, distributed over time, that drives lasting neurological adaptation.
The most honest summary is this: intensity determines what you're training; volume determines whether you actually get enough of it to adapt.
References
Donnellan-Fernandez K, Ioakim A, Hordacre B. Revisiting dose and intensity of training: Opportunities to enhance recovery following stroke. Journal of Stroke and Cerebrovascular Diseases. 2022;31(11):106789. doi:10.1016/j.jstrokecerebrovasdis.2022.106789
Fang CY, Lien ASY, Tsai JL, Yang HC, Chan HL, Chen RS, Chang YJ. The effect and dose-response of functional electrical stimulation cycling training on spasticity in individuals with spinal cord injury: A systematic review with meta-analysis. Frontiers in Physiology. 2021;12:756200. doi:10.3389/fphys.2021.756200
Gauthier LV, Ravi R, DeLuca D, Zhou W. Dose response to upper extremity stroke rehabilitation varies by individual: Early indicators of treatment response. *Stroke*. 2024;55(3):696-704. doi:10.1161/STROKEAHA.123.045039
Huh S, Kim Y, Ko HY, Yun MS, Shin YI, Lee JL, Ko SH. Effectiveness of a community-based exercise program for ambulatory individuals with spinal cord injury: A randomized controlled trial. Archives of Physical Medicine and Rehabilitation. 2025;106(4):481-489. doi:10.1016/j.apmr.2024.10.013
Kuhn D, Leichtfried V, Schobersberger W. Four weeks of functional electrical stimulated cycling after spinal cord injury: A clinical cohort study. International Journal of Rehabilitation Research. 2014;37(3):243-250. doi:10.1097/MRR.0000000000000062
Lang CE, MacDonald JR, Reisman DS, Boyd L, Jacobson Kimberley T, Schindler-Ivens SM, Hornby TG, Ross SA, Scheets PL. Observation of amounts of movement practice provided during stroke rehabilitation. Archives of Physical Medicine and Rehabilitation. 2009;90(10):1692-1698. doi:10.1016/j.apmr.2009.04.005
Palermo AE, Nash MS, Kirk-Sanchez NJ, Cahalin LP. Adherence to and impact of home-based high-intensity IMT in people with spinal cord injury: A pilot study. Spinal Cord Series and Cases. 2022;8:85. doi:10.1038/s41394-022-00551-5
Park JM, Park HJ, Yoon SY, Kim YW, Shin JI, Lee SC. Effects of robot-assisted therapy for upper limb rehabilitation after stroke: An umbrella review of systematic reviews. *Stroke*. 2025;56(5):1243-1252. doi:10.1161/STROKEAHA.124.048183
Sadowsky CL, Hammond ER, Strohl AB, Commean PK, Eby SA, Damiano DL, Wingert JR, Bae KT, McDonald JW 3rd. Lower extremity functional electrical stimulation cycling promotes physical and functional recovery in chronic spinal cord injury. Journal of Spinal Cord Medicine. 2013;36(6):623-631. doi:10.1179/2045772313Y.0000000101
Shields RK, Dudley-Javoroski S. Monitoring standing wheelchair use after spinal cord injury: A case report. Disability & Rehabilitation. 2005;27(3):142-146. doi:10.1080/09638280400009337
Washington State Health Care Authority. Standing frames: Effectiveness and safety rapid review. November 2019. Available at: https://www.hca.wa.gov/assets/program/rapid-review-standing-frames.pdf