The effect of FES Cycling on bone density

Combining a passive/active exercise bike with synchronised FES (Functional Electrical Stimulation) is a well-researched and well-known exercise modality for persons to use after a spinal cord injury or other neurological condition.  One of the benefits often sought by our spinal cord injured clients is preservation of bone density and we will look at the evidence for this in this article. Bone is a dynamic tissue - it responds to the needs placed upon it - getting stronger under load and weaker in the absence of load. Paralysis after a spinal cord injury and lack of activity that loads the bones results in a loss of bone strength and increased risk of fractures.. FES Cycling is one way of helping to prevent this.

What is an FES Cycling system?

The RehaMove 2 system from Hasomed we work with is one of the best known “fes bike” systems world wide and we will explain the idea behind this approach. Most available systems have a similar intention. They may have differences in presentation but the results of use should be similar.
When paralysed limbs prevent the person from pedalling a bike as normal, electrical stimulation, synchronised with the movement of the pedals can allow that person to exercise using their own leg muscles; or indeed arm and shoulder muscles too when appropriate.

Why use an FES bike?

RehaMove 2

This version of the RehaMove 2 FES Cycling system features the MOTOmed Loop L bike and supports leg exercise with 8 channels of FES

Typically the passive/active bike used by itself, would be capable of moving the persons legs, despite paralysis, due to the built-in motor. This has value in reducing the risk of contractures and may have some circulation enhancing effect but has relatively little overall exercise effect.  Adding FES has been shown to offer a number of benefits, including long-term cardiovascular fitness, improved peripheral circulation and preserved bone density. Muscle mass and tissue quality can be preserved which many users appreciate for the improved appearance of their legs as well as the health benefits. Paralysed muscle changes its structure, and overall presents a poor trophic situation for the longer term. Using FES Cycling ensures that a strong muscle contraction takes place despite the paralysis thereby preserving muscle and tissue health.

With a so-called complete spinal cord injury the computer controlled stimulation of the muscles is used to pedal the bike and the exercise is active. This is because It is the users leg muscles that are pedalling the bike despite the paralysis.

In cases of incomplete spinal cord injury, or indeed conditions such as MS, stroke or Parkinson's, the user may well be able to consciously pedal the bike; perhaps only if the resistance is low and for a short period of time, but nevertheless the user can actively contribute some effort.

In such cases FES Cycling can support the user very effectively. When the system senses that the user can contribute effort for themselves the stimulation is reduced. When the system senses that the user can no longer consciously contribute, the stimulation intensity is automatically increased to encourage active cycling again. The stimulation intensity is always maintained within safe limits and may in these cases be limited by any preserved sensation. Over time, the user can experience a training effect and work for longer periods, against higher levels of resistance or at greater speed. This takes some commitment but we have many users who make such a commitment as they see the health benefits as important for long term health.

We would love every one who could benefit to have access to an fes cycle. However, in the UK the majority of our clients have experienced a catastrophic injury resulting in a spinal cord injury. A medico-legal case is often the source of funding and justified because the evidence supporting the use of FES Cycling is so strong.

As in much of rehabilitation, the “dose” of the intervention strongly influences any benefit. The first rule of exercise after all, is you have to “turn up and do it”.  We have been working with FES Cycling for more than 15 years now and are always pleased to see clients working effectively at home with these systems.

One of our clients is Claire Lomas, now on her second generation of RehaMove and a great advocate of FES Cycling. This short video really showcases her commitment.

Claire Lomas descirbes her commitment to using FES Cycling and the RehaMove system

Bone density and exercise effects

Disuse of the limbs and lack of loading after spinal cord injury contributes to a decline in bone density which is correlated to the time since injury. As a rule of thumb some 40% decline is experienced within 3 years and progression typically plateaus around 7 years post-injury. The only way of knowing how strong the bones are is via a test. A “bone density scan” typically uses low dose X-rays to see how dense (or strong) your bones are. You may also hear it called a DEXA scan. Some therapy methods require a DEXA scan prior to commencing them if there is a potential risk.

In order to respond to load, bones must have a mechanism that can sense loading and signal the need for chnage. The main sensor of mechanical forces is the osteocytes network, which transmits orders to effector cells (osteoclasts, and osteoblasts), by the secretion of several cytokines which modulate the concentration of the bone microenvironment. Like so much to do with the body, we still dont fully understand how this works.

However, cycling with functional electrical stimulation has been shown to improve lower-extremity bone strength or mineral density for adults with a spinal cord injury; (1,2,3) however, results are mixed (4,5) and outcomes hampered by inadequate intensity of load applied to the bone.  Similarly FES Rowing has been shown to have beneficial effects (7)

There has been less research focused on passive cycling or indeed children with spinal cord injuries. (8)

There are a few conclusions that we can draw in relation to the effect of FES Cycling on bone density.

First of all, early intervention is best as it is easier to preserve the bone mineral density rather than reverse the effect of disuse. Secondly, the dose of FES Cycling matters.  Some studies have found little or no benefit to bone density (9) if the loads are too low so it is important to pay attention to the intensity of stimulation which will have the effect of increasing the repetitive load on the bones.

By exercise dose, we are pointing to the duration and overall intensity of exercise.  In the first few weeks of starting to use a RehaMove system, the user can gradually expect to increase the intensity of stimulation until they can consistently generate sufficient power to be actively cycling against resistance for the whole session. We dont know for sure how to be certain the dose is sufficient to preserve bone density but we do know that higher loading is better.

Further reading

1. Belanger M, Stein RB, Wheeler GD, Gordon T, Leduc B . Electrical stimulation: can it increase muscle strength and reverse osteopenia in spinal cord injured individuals? Arch Phys Med Rehabil 2000; 81: 1090–1098.Chen SC, Lai CH, Chan WP, Huang MH, Tsai HW, Chen JJ . Increases in bone mineral density after functional electrical stimulation cycling exercises in spinal cord injured patients. Disabil Rehabil 2005; 27: 1337–1341.

2. Frotzler A, Coupaud S, Perret C, Kakebeeke TH, Hunt KJ, Donaldson Nde N et al. High-volume FES-cycling partially reverses bone loss in people with chronic spinal cord injury. Bone 2008; 43: 169–176.

3. Sloan KE, Bremner LA, Byrne J, Day RE, Scull ER . Musculoskeletal effects of an electrical stimulation induced cycling programme in the spinal injured. Paraplegia 1994; 32: 407–415.

4. BeDell KK, Scremin AM, Perell KL, Kunkel CF . Effects of functional electrical stimulation-induced lower extremity cycling on bone density of spinal cord-injured patients. Am J Phys Med Rehabil 1996; 75: 29–34.

5. Dudley-Javoroski S, Shields RK . Muscle and bone plasticity after spinal cord injury: review of adaptations to disuse and to electrical muscle stimulation. J Rehabil Res Dev 2008; 45: 283–296.

6. Effects of FES-Rowing Exercise on the Time-Dependent Changes in Bone Microarchitecture After Spinal Cord Injury: A Cross-Sectional Investigation. Adina E Draghici, J Andrew Taylor, Mary L Bouxsein, Sandra J Shefelbine. First published: 08 May 2019. https://doi.org/10.1002/jbm4.10200

7. Lauer, R., Smith, B., Mulcahey, M. et al. Effects of cycling and/or electrical stimulation on bone mineral density in children with spinal cord injury. Spinal Cord 49, 917–923 (2011). https://doi.org/10.1038/sc.2011.19

8. Leeds EM, Klose KJ, Ganz W, Serafini A, Green BA. Bone mineral density after bicycle ergometry training. Archives of Physical Medicine and Rehabilitation. 1990 Mar; 71(3):207-209. PMID: 2317139.