This glossary covers the technical and clinical terms used in this book. Definitions are written for the general reader rather than the specialist, and follow the way the words are used here. Where a term appears frequently, the relevant chapters are noted in parentheses.
A
Action potential. The brief electrical signal that travels along a nerve fibre when it is stimulated strongly enough. In FES, the purpose of each electrical pulse is to trigger an action potential in the motor nerve. (Ch 2)
Active cycling. The phase of a session in which your own muscles are contracting and doing real work against the bike's resistance. Contrast with passive cycling. (Ch 1, 9, 10)
Active Hand. A simple product used during upper-limb FES to help the hand hold on to a handle when grip is weak.
Adaptive mode. A stimulator setting that automatically raises or lowers the pulse width during a session so that you keep cycling at a target speed, even as the muscles tire. (Ch 9, 10)
Adherence. Whether you actually complete your training sessions. In rehabilitation, adherence is the foundation on which all other gains rest. (Ch 5, 10)
Adhesive electrode pads. Self-stick pads are placed on the skin over a muscle, through which the stimulator delivers its pulses. Replaced periodically as they wear out.
Aerobic metabolism. The oxygen-using energy system that fuels sustained, endurance-type activity. Used mainly by Type I muscle fibres. (Ch 2)
Alpha motor neuron. The largest nerve cell in the spinal cord whose job is to drive muscle contraction. FES works by activating these neurons through surface electrodes. (Ch 2)
Anaerobic glycolysis. The oxygen-free energy system is used for short, powerful efforts. The main fuel path for Type IIx muscle fibres.
Ankle-foot orthosis (AFO). A brace that holds the ankle in position; used in positioning programmes to prevent tightness and protect the heel. (Ch 11)
ASIA classification. The American Spinal Injury Association scale is used to describe a spinal cord injury. ASIA A is complete; ASIA B, C, and D describe progressively more preserved function. (Ch 1, 5)
Atrophy. Loss of muscle bulk from disuse. Common after paralysis and reversible, in part, with FES cycling. (Ch 4, 10)
Autonomic dysreflexia. A sudden and potentially dangerous rise in blood pressure triggered by a stimulus below the level of a spinal cord injury, typically at or above the sixth thoracic level (T6). Worth learning to recognise before starting a programme. (Ch 6, 7, 9)
Autonomic nervous system. The part of the nervous system that controls involuntary functions: heart rate, blood pressure, digestion, sweating, temperature. Often disturbed after SCI. (Ch 10, 11)
B
Baclofen. A commonly prescribed anti-spasticity medication. (Ch 11)
BerkelBike. A Dutch recumbent FES tricycle that allows outdoor cycling. (Ch 3)
Biphasic rectangular pulse. The shape of the electrical pulse used by modern FES stimulators: a quick positive phase followed by a balancing negative phase. (Ch 2)
Bone mineral density. A measure of bone strength. Reduced after prolonged paralysis, and partially addressed by weight-bearing and FES. (Ch 4, 6)
C
Cadence. Pedalling speed, usually measured in revolutions per minute (rpm). (Ch 3, 5)
Carbonhand. A soft robotic glove that adds strength to a weak grip during daily tasks and upper-limb rehab. (Ch 11)
Cardiac pacemaker. An implanted heart device. An absolute contraindication to FES: do not use FES if you have one. (Ch 6, 7)
Case manager. A coordinator, usually appointed as part of a medico-legal settlement or insurance claim, who oversees a client's rehabilitation, equipment, and funding.
Cauda equina. The bundle of nerve roots that extends below the end of the spinal cord itself. Injury to the cauda equina produces a lower motor neuron lesion. (Ch 5, 6)
CE mark. The European conformity mark showing that a device meets regulatory safety standards. Required on all medical devices sold in Europe.
Central nervous system. The brain and spinal cord. (Ch 5)
Cerebral palsy. A developmental condition, present from birth or early infancy, that affects movement and posture.
Channel. A single output on a stimulator, connected to one pair of electrodes. Most FES systems have between four and eight channels. (Ch 1, 8, 9)
Closed-loop control. Stimulation that is adjusted automatically using feedback from sensors on the bike. The opposite is open-loop control. (Ch 3)
Complete spinal cord injury. An injury in which no motor or sensory function is preserved below the level of the lesion. Does not necessarily mean that the cord itself has been severed. (Ch 1, 5)
Consumables. Items that wear out and need replacing: electrode pads, cables, batteries. Budget for these from the start. (Ch 8)
Contracture. A fixed tightness or shortening of muscle and connective tissue around a joint, restricting movement. Prevention is far easier than correction. (Ch 6, 7, 11)
Contraindication. A medical reason not to use a particular treatment. Absolute contraindications exclude FES entirely; relative contraindications mean it may still be possible with extra care. (Ch 6, 7)
Cortical reorganisation. Change in the brain's motor areas as a result of experience and training. One of the hoped-for outcomes of intensive repetition. (Ch 4, 10)
Cross-sectional area (CSA). A way of measuring muscle size by imaging a slice through it, typically through the thigh. A common outcome measure in FES research. (Ch 4, 5)
Current. The intensity of each stimulation pulse, measured in milliamps (mA). In a current-controlled stimulator, the set current is delivered regardless of small changes in skin contact. (Ch 2, 8, 9)
D
Deep vein thrombosis (DVT). A blood clot in a deep vein, usually of the leg. An absolute contraindication to FES while active. (Ch 6, 7)
Denervated muscle. Muscle that has lost its nerve supply. Does not respond to standard FES; requires specialised stimulators and protocols. (Ch 2, 5, 6)
DEXA scan. A low-dose X-ray scan used to measure bone density.
Disuse. Prolonged lack of muscle activity. The main cause of atrophy and fibre-type shift after paralysis. (Ch 2, 4)
Dose. In rehabilitation, the total amount of training: how often (frequency), how long (volume), and how hard (intensity). (Ch 4, 10, 11)
Duty cycle. The ratio of time a stimulator is "on" versus "off" during a session. Used to shape work and rest.
E
Electrode cables. The leads that connect each channel of the stimulator to its electrode pads. (Ch 7, 8)
Electrotherapy. The broad field of using electrical energy for therapeutic purposes. FES is one branch. (Ch 2, 3)
ERGYS. One of the earliest commercial FES cycling systems, FDA-cleared in 1984. (Ch 3)
Exercise ergometer. A rehabilitation exercise bike fitted with measurement instruments for resistance, power, and distance. (Ch 1, 3, 8)
F
Fast-twitch fibres. Muscle fibres (Types IIa and IIx) that produce rapid, powerful contractions but tire quickly. Preferentially recruited by FES. (Ch 9, 10)
Fatigue. The progressive loss of force during a session. Normal in the early weeks and a guide to dosing the training. (Throughout)
FDA clearance. The US Food and Drug Administration's authorisation for a medical device.
Femoral artery. The main artery supplying the thigh. Its diameter is a measurable marker of vascular adaptation to training. (Ch 4, 6)
FES (Functional Electrical Stimulation). The use of electrical pulses to make weak or paralysed muscles contract in a useful, coordinated way. (Throughout)
FES cycling. Cycling driven by timed electrical stimulation of leg, and sometimes arm, muscles; the subject of this book. (Throughout)
Fibre-type shift. The change in proportions of slow and fast muscle fibres that follows disuse, and can be partially reversed by training. (Ch 2, 4, 9)
Forced exercise. Exercise performed at a rate faster than the person would choose voluntarily. Shown to produce unusual benefits in Parkinson's disease. (Ch 5)
Fracture (active). An unhealed broken bone in the limb to be exercised. An absolute contraindication to FES. (Ch 1, 6)
Frequency. The number of stimulation pulses delivered per second, measured in hertz (Hz). Most FES cycling starts at around 30 to 35 Hz. (Ch 2, 4, 8, 9, 10)
G
Galvani, Luigi. The 18th-century Italian scientist whose frog-leg experiments laid the groundwork for the whole field of electrotherapy. (Ch 3)
Gluteal muscles. The muscles of the buttocks; often included in FES cycling programmes. (Ch 1, 3, 8)
Guillain-Barré syndrome. A neurological condition, often triggered by infection, that can weaken the limbs and from which recovery may be assisted by FES.
H
Hamstrings. The muscles at the back of the thigh.
Heart rate variability (HRV). The small variations between successive heartbeats. A useful marker of autonomic balance. (Ch 11)
Hemiparesis / hemiplegia. Weakness or paralysis of one side of the body, typically after a stroke. (Ch 5)
Hertz (Hz). The unit of frequency: pulses per second.
I
IEC 60601. The international electrical safety standard that all medical-grade stimulators must meet. (Ch 8)
Incomplete spinal cord injury. An injury in which some motor or sensory function is preserved below the level of the lesion. (Ch 1, 4, 5)
Indego. A powered lower-limb exoskeleton used in some rehabilitation settings.
Innervation / reinnervation. The state of having an intact nerve supply to a muscle; reinnervation is the regrowth of nerve connections after damage. (Ch 2, 5)
Insulin sensitivity. How effectively the body's tissues respond to insulin. Improved by regular exercise, including FES cycling. (Ch 10)
Intramuscular fat. Fat deposited within muscle tissue. Increases with disuse; reduces with training. (Ch 4, 5)
Ischial tuberosities. The "sitting bones" at the base of the pelvis; the main weight-bearing points when seated, and the commonest site of pressure ulcers. (Ch 11)
L
Lower motor neuron (LMN). The nerve cells running from the spinal cord out to the muscles. FES relies on these being intact. (Ch 1, 2, 5, 6)
Lower motor neuron lesion. Damage to the peripheral motor nerves themselves, producing denervated muscle. Distinct from an upper motor neuron lesion and requires different treatment.
M
Medico-legal funding. Money received through a legal claim after an injury. The commonest route by which UK clients fund FES cycling.
Meta-analysis. A research method that pools results from many studies to give a single summary estimate of an effect. (Ch 4, 5)
Microprocessor. The small computer chip that, from the late 1970s onward, made coordinated FES cycling possible. (Ch 3)
Microsecond. One-millionth of a second. The unit in which pulse width is measured.
Milliamp (mA). One-thousandth of an amp. The unit in which FES current is measured.
Mirror therapy. A stroke rehabilitation technique using a mirror placed between the arms to create the visual illusion of movement in the affected hand. (Ch 11)
Mitochondria. The energy-producing structures inside cells. Grown in number and capacity by endurance training. (Ch 10)
Modified Ashworth Scale (MAS). A clinical scale for grading spasticity from 0 (none) to 4 (rigid). (Ch 4)
Motor unit. A single motor neuron together with all the muscle fibres it controls. The functional unit of voluntary movement. (Ch 2)
MOTOmed. A range of passive and active rehabilitation bikes commonly paired with FES stimulators. (Ch 1, 3, 8)
Multiple sclerosis (MS). A condition in which the immune system attacks the myelin sheath of nerves in the central nervous system.
Muscle pump. The action by which muscle contraction compresses veins and helps return blood to the heart. Particularly important after SCI. (Ch 4, 6)
MyoCycle. A US-designed FES cycling system.
Myelin sheath. The fatty insulation around nerve fibres that speeds signal transmission. Damaged in MS. (Ch 5)
Myoglobin. An oxygen-storing protein found in abundance in slow-twitch muscle fibres, giving them their red colour. (Ch 2)
N
Neuromodulation. Techniques that modulate activity in the nervous system, including tSCS and tVNS. (Ch 11)
Neuromuscular electrical stimulation (NMES). Electrical stimulation applied for targeted muscle strengthening or rehabilitation, in a clinical rather than functional context. (Ch 2, 8)
Neuropathic pain. Pain arising from damage or dysfunction in nerves themselves, rather than from injured tissue.
Neuroplasticity. The nervous system's ability to form new connections and change in response to experience. The mechanism underlying most functional recovery. (Ch 4, 5, 10, 11)
NICE. The UK's National Institute for Health and Care Excellence. Produces clinical guidelines and assesses cost-effectiveness of treatments for the NHS.
Noxious stimulus. Any irritant (a full bladder, a tight strap, skin damage) below the level of an SCI that may trigger autonomic dysreflexia. (Ch 9)
O
Oedema. Swelling caused by fluid accumulation in tissues. Often reduced by FES cycling in the lower limbs. (Ch 1, 4)
Open-loop control. Stimulation delivered on a fixed pattern without feedback from the user or the bike. Contrast with closed-loop control. (Ch 3)
Orthostatic hypotension. A drop in blood pressure on becoming upright, causing light-headedness or fainting. Common after SCI. (Ch 9)
Osteoporosis. Severe thinning of bone. A relative contraindication to FES: possible with care. (Ch 6)
P
Paraplegia. Paralysis of the lower limbs, and sometimes part of the trunk, following an injury below the cervical spine.
Parasympathetic nervous system. The "brake" side of the autonomic nervous system; promotes rest, digestion, and recovery. Targeted by tVNS. (Ch 11)
Parkinson's disease. A progressive neurological condition characterised by tremor, rigidity, and slowness of movement (bradykinesia).
Passive cycling. Motor-driven cycling in which the legs are moved without the muscles contracting. Used as a warm-up and for users for whom active cycling is not possible. (Ch 1, 3, 4, 8, 9)
Peripheral nerves. Nerves outside the brain and spinal cord. Damage to peripheral nerves causes denervated muscle. (Ch 1, 2, 5)
Petrofsky, Jerrold. The US researcher who, in the 1980s, demonstrated that FES cycling was possible for people with complete SCI. (Ch 3)
Pendulum test. A clinical test of spasticity in which the lower leg is released and allowed to swing. Greater damping indicates more spasticity. (Ch 4)
Perceived exertion. A subjective rating of how hard exercise feels. A useful guide to training intensity when heart rate is unreliable. (Ch 10)
Power output. The mechanical work rate a person is producing on the bike, measured in watts. (Ch 4, 5, 9, 10)
PRAFO. A specific brand of ankle-foot orthosis used for pressure relief at the heel and for ankle positioning. (Ch 11)
Pressure ulcer. A wound caused by sustained pressure over a bony prominence. A serious risk in SCI, and a reason for attention to positioning.
Pulse width. The duration of each stimulation pulse, measured in microseconds. Typically starts at 250 and can be progressed up to around 500. (Ch 2, 8, 9, 10)
Q
Quadriceps. The large group of muscles at the front of the thigh. Central to both voluntary and FES-driven cycling.
Quality-adjusted life year (QALY). A measure used by NICE to weigh up the cost-effectiveness of treatments for NHS funding decisions.
R
Ramp. The gradual build-up of stimulation intensity at the start of each contraction, and its gradual fall at the end, to produce smooth movement. (Ch 9)
Range of motion. How far a joint can move in each direction. Preserved by regular cycling and standing. (Ch 1, 6, 7, 10)
Recumbent bike. A bike with a reclined seat and pedals placed in front of the rider, rather than below. (Ch 3)
RehaMove / RehaStim. FES stimulators developed by Hasomed; widely used in FES cycling with the MOTOmed range of bikes. (Ch 1, 3, 8)
Renshaw cell. An interneuron in the spinal cord that helps regulate motor neuron firing. Relevant to how FES may influence spasticity. (Ch 4)
Resistance training. Exercise performed against a load to build strength. (Ch 4, 10)
RISE stimulator. A specialised stimulator developed in the European RISE research programme for the stimulation of denervated muscle. (Ch 2, 5)
RT300. An integrated FES cycling system produced by Restorative Therapies. (Ch 3, 8)
S
SCI (spinal cord injury). Damage to the spinal cord producing paralysis, sensory loss, and autonomic disturbance below the level of the lesion.
Sensory neurons. Nerves carrying information from the body toward the brain.
Six-minute walk test. A standard test of endurance and mobility, measuring the distance covered in six minutes. (Ch 5)
Slow-twitch fibres. Muscle fibres (Type I) that contract slowly, fatigue slowly, and rely on aerobic metabolism. (Ch 2)
Spasticity. Increased muscle tone and involuntary contractions resulting from an upper motor neuron lesion. A common symptom after SCI, stroke, and MS, and often improved by regular FES cycling.
Standing frame. A device that supports a person in the upright position. Used alongside FES cycling to load the long bones and stretch the hip flexors. (Ch 6, 11)
Stim2Go. A universal, standalone, smartphone-controlled FES stimulator developed by SensorStim Neurotechnology. Supports FES cycling, NMES, tSCS, and TENS through a single device. (Ch 1, 3, 4, 6, 7, 8, 10, 11)
Stimulator. The programmable device that generates and controls the electrical pulses delivered to the electrodes.
Strength-duration assessment. A clinical test that helps determine whether the motor nerves to a muscle are intact (and so whether standard FES will work). (Ch 2)
Stroke. Damage to the brain caused by interruption of its blood supply, either by a blocked vessel (ischaemic) or a ruptured vessel (haemorrhagic).
Subluxation. A partial dislocation of a joint. A specific concern at the shoulder in upper-limb rehabilitation after stroke. (Ch 11)
Surface electrodes. Electrodes placed on the skin rather than implanted. The usual choice for home FES cycling.
Sympathetic nervous system. The "accelerator" side of the autonomic nervous system; prepares the body for action. (Ch 11)
T
Talk test. A simple way of judging exercise intensity: if you can just hold a conversation, you are in the right zone for endurance work. (Ch 10)
Task-specific practice. The rehabilitation principle that the nervous system learns best by practising the actual task you want to improve. (Ch 4, 5, 11)
Tek RMD. A mobility and standing device that allows a user to transfer, stand, and move independently.
Telerehabilitation. Remote clinical review and adjustment of a home programme using video calls and data logged by the equipment. (Ch 10)
TENS (Transcutaneous Electrical Nerve Stimulation). Electrical stimulation used primarily for pain management. Similar technology to FES but used for a different purpose. (Ch 2, 8)
Thermoregulation. The body's control of its own temperature. Often impaired after SCI. (Ch 10)
THERA-Trainer. A range of passive and active bikes used with FES stimulators, similar in role to the MOTOmed range. (Ch 1, 3, 8)
Thoracic spine. The middle section of the spine, numbered T1 to T12. The sixth thoracic level (T6) is the usual cut-off above which autonomic dysreflexia is a serious concern.
Transcutaneous. Applied through intact skin, rather than implanted. FES, tSCS, tVNS, and TENS are all transcutaneous techniques.
Transcutaneous spinal cord stimulation (tSCS). Electrical stimulation applied through the skin over the spinal cord to increase the excitability of neural circuits. Approved in Europe for temporary reduction of spasticity. (Ch 4, 8, 11)
Transcutaneous vagus nerve stimulation (tVNS). Electrical stimulation of the vagus nerve through the skin, typically at the ear, used to influence the autonomic nervous system. (Ch 11)
Transfer. The act of moving between one surface and another, for example from wheelchair to bike seat. A daily skill for most users of this book. (Ch 7, 9)
Transverse myelitis. Inflammation affecting a cross-section of the spinal cord, producing symptoms similar to a spinal cord injury. (Ch 5)
Traumatic brain injury. Brain injury from an external force. May produce lower-limb weakness amenable to FES. (Ch 5)
Type I, IIa, IIx fibres. The three main categories of skeletal muscle fibre, from slow and fatigue-resistant (I) through to fast and powerful but fatigable (IIx). (Ch 2, 4)
U
Upper motor neuron (UMN). The nerve pathways running from the brain down through the spinal cord. Damage above the lower motor neuron produces spasticity and preserved peripheral responses. (Ch 1, 2, 5)
V
Vagus nerve. The longest cranial nerve, carrying parasympathetic fibres to most of the internal organs. The target of tVNS. (Ch 11)
Vascular resistance. The resistance the blood vessels offer to flow. Reduced by regular FES cycling, improving circulation. (Ch 4, 6)
Venous return. The flow of blood back to the heart. Assisted by the muscle pump during FES cycling. (Ch 4)
Voltage-controlled. A simpler stimulator design, used in most consumer TENS units, that sets a target voltage rather than a target current. Less suitable than current-controlled designs for serious rehabilitation use. (Ch 8)
VO2peak. Peak oxygen uptake during exercise. The standard laboratory measure of aerobic fitness. (Ch 4)
Volta, Alessandro. The 18th-century physicist, contemporary and sometime rival of Galvani, whose work on the electrical battery made controlled stimulation possible. (Ch 3)
W
Watt. The unit of power; a measure of the work rate produced on the bike.
Waveform. The shape of an electrical pulse plotted over time. Modern FES uses a biphasic rectangular waveform. (Ch 2)
Weight-bearing. Loading bones and joints in the upright position. Important for bone density and best delivered through regular standing alongside cycling. (Ch 4, 6, 11)
Z
Zone 2. A moderate exercise intensity, sustainable for long periods, at which the body relies mainly on fat for fuel and conversation is just possible. The base on which most endurance training is built. (Ch 10)