Intensity Matters:

Summary of Evidence 

Sub-Acute Stroke and Motor Incomplete Spinal Cord Injury (iSCI)

Contributor: George Hornby, PT, PhD

Over the past 20 years, published evidence has highlighted the potential utility of locomotor training (i.e., walking or stepping training) at higher cardiovascular intensities to improve mobility impairments post-stroke. This strategy utilizes key principles of neuroplasticity, including the specificity, amount, and intensity of motor training, that can strengthen neural pathways contributing to locomotor function and lead to long-term changes in mobility.  While the goal during training is to achieve higher cardiovascular intensities and is typically measured using heart rate, increased cardiovascular demands are reflective of the enhanced muscular demands for oxygen to sustain the locomotor activities, which is in turn driven by increased neural activity (i.e., increased neural recruitment and firing rates). Such increases in activity of neural circuits subserving locomotor tasks thereby results in short- and long-term changes in neural connectivity, which serves as the bases for improved locomotor function.

For individuals with subacute stroke, controlled trials and implementation efforts in the US, Canada and Norway have demonstrated that efforts to perform HIT during subacute stroke rehabilitation results in greater gains in walking outcomes as compared to conventional strategies.  Additional studies have also been published in patients with iSCI, with HIT focused on walking training superior to lower-intensity training or high-intensity impairment-based interventions.

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Parkinson Disease

Contributor: Terry Ellis, PT, PhD

Across most studies of aerobic exercise in Parkinson disease, moderate intensity exercise is generally defined as 60% to 75% of maximum heart rate (HR), whereas high intensity exercise is defined as 75% to 85% of maximum HR.  However, some studies use a percentage of HR reserve or a percentage of VO₂ max to determine exercise intensity.  Importantly, some studies encompass aerobic exercise that started at moderate intensity and gradually increased to high intensity whereas other studies define target intensities that span the moderate to high ranges.

Most aerobic exercise studies in individuals with PD consist of walking on a treadmill or stationary cycling. Results across studies using different modes of aerobic exercise are comparable suggesting no one form of aerobic exercise is superior to another. This provides participants the option of choosing the mode of aerobic exercise that they enjoy most, thereby optimizing long-term adherence.

Summary of Evidence:

• Studies in PD reveal that moderate to high intensity aerobic exercises in Parkinson disease improves oxygen consumption (VO₂) suggesting a specificity of training effect.
• Studies in PD reveal that moderate to high intensity aerobic exercises in Parkinson disease reduces motor disease severity suggesting a potential disease modifying effect.Effects are particularly apparent during the early stages of PD (H&Y 1-2) and during the medication “off” state or in those with de novo PD.This suggests the importance of prescribing higher intensity aerobic training early in course of PD.
• Studies in PD reveal that moderate to high intensity aerobic exercises in Parkinson disease improve functional outcomes and quality of life.Improvements in function encompass walking, balance and ADL’s outcomes.

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Multiple Sclerosis

Contributors:

Evan Cohen, PT, PhD, NCS; Herb Karpatkin, PT, DSc, NCS

Summary of Evidence:

• The evidence is clear that it is safe for people with MS to undertake exercise
• There are several systematic reviews of the literature that make recommendations for strength training, aerobic training, and a combination of strength and aerobic training for people with MS, though these do not specify details about high intensity training:
• High intensity exercise is safe and feasible in MS. Persons with MS can tolerate very high exercise loads as long as they are interspersed with rest breaks This type of training results in improved outcomes for persons with MS when contrasted with lower intensity continuous training.
• Three studies, while not using explicit high intensity interval training, all provide evidence that walking interspersed with rest breaksfor pwMS results in better walking performance than continuous walking. One study intersperses very fast short walks (20 seconds) with long recoveries, finding improvements in both 6 minute walk test performance and MBT scores. Unlike the other studies, physiologic variables were not measured.

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