The Physiology of Exercise in Spinal Cord Injury

286 Pages·2016·5.05 MB·English

by  J. Andrew Taylor (eds.)

Physiology in Health and Disease
J. Andrew Taylor Editor
The Physiology
of Exercise in
Spinal Cord
Injury
Physiology in Health and Disease
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J. Andrew Taylor
Editor
The Physiology of Exercise
in Spinal Cord Injury
Editor
J.AndrewTaylor
PhysicalMedicine&Rehabilitation
HarvardMedicalSchool
SpauldingHospitalCambridge
Cambridge,Massachusetts
USA
PhysiologyinHealthandDisease
ISBN978-1-4939-6662-2 ISBN978-1-4939-6664-6 (eBook)
DOI10.1007/978-1-4939-6664-6
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Contents
1 ThePhysiologyofExerciseinSpinalCordInjury(SCI):
AnOverviewoftheLimitationsandAdaptations. . . . . . . . . . . . . . 1
HannahW.MercierandJ.AndrewTaylor
2 PhysiologyofMotorDeficitsandthePotentialofMotor
RecoveryAfteraSpinalCordInjury. . . . . . . . . . . . . . . . . . . . . . . 13
V.ReggieEdgertonandRolandR.Roy
3 RoleofActivityinDefiningMetabolicandContractile
AdaptationsAfterSCI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
GaelleDeley
4 RespiratorySystemResponsestoExerciseinSpinalCordInjury... 51
ChristopherR.West,AndrewW.Sheel,andLeeM.Romer
5 AlterationsinCardiacElectrophysiologyAfterSpinalCord
InjuryandImplicationsforExercise. . . . . . . . . . . . . . . . . . . . . . . 77
HeidiL.LujanandStephenE.DiCarlo
6 CardiovascularResponsestoExerciseinSpinalCordInjury. . . . . 105
ThomasJ.Barton,DavidA.Low,andDickH.J.Thijssen
7 ThermoregulatoryConsiderationsforthePerformanceof
ExerciseinSCI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127
ChristopherT.MinsonandViennaE.Brunt
8 IncreasedBoneFractureAfterSCI:CanExerciseReduceRisk?. . . 161
AdinaE.DraghiciandSandraJ.Shefelbine
9 AlterationsinBodyCompositionAfterSCIandtheMitigating
RoleofExercise. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
DavidR.GaterandGaryJ.Farkas
v
vi Contents
10 CardiometabolicSyndromeinSCI:TheRoleofPhysical
DeconditioningandEvidence-BasedCountermeasures. . . . . . . . . . 199
JenniferL.Maher,DavidW.McMillan,andMarkS.Nash
11 TheEffectofAcuteandChronicExerciseonInflammatory
MarkersinSCI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
ChristofA.LeichtandNicoletteC.Bishop
12 RoleofExerciseinAlleviatingChronicPaininSCI. . . . . . . . . . . . 233
ThomasN.Bryce
13 AutonomicAlterationsAfterSCI:ImplicationsforExercise
Performance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
AaronA.PhillipsandAndreiV.Krassioukov
14 HybridFunctionalElectricalStimulationExercisefor
ImprovedCardiorespiratoryFitnessinSCI. . . . . . . . . . . . . . . . . . 269
ShuangQiuandJ.AndrewTaylor
Chapter 1
The Physiology of Exercise in Spinal Cord
Injury (SCI): An Overview of the Limitations
and Adaptations
HannahW.MercierandJ.AndrewTaylor
Abstract Forallhumanbeings,exerciseisvitaltolivingwell.Exercisepromotes
physical and psychological health across the lifespan, reducing risk for mortality
and decreasing prevalence of health complications which contribute to chronic
disease. Exercise requires integrated physiologic responses across the musculo-
skeletal, cardiovascular, autonomic, pulmonary, thermoregulatory, and immuno-
logicsystems.However,personslivingwithspinalcordinjury(SCI)havedifficulty
achieving the minimal exercise requirements for health benefits since paralyzed
skeletalmusclescannotcontributetooveralloxygenconsumption.Moreover,SCI
can be considered as an accelerated systemic form of aging due to the severely
restrictedphysicalinactivityimposed,usuallyatanearlyage.Indeed,personswith
SCI experience profound declines in function across many physiological systems
andareconsidered,asagroup,tobesedentaryandamongtheleastfitindividuals.
And, there are numerous considerations for exercise in those with an SCI. Alter-
ationsinfunctionacrossalmostallthephysiologicalsystemsengagedbyexercise
may be compromised or altered. Nonetheless, exercise can still confer significant
benefitsandmaybeamongthemostimportantcomponentsofahealthylifestylefor
thispopulation.
After SCI, the motor, sensory, and autonomic deficits limit not only the conve-
nience of exercising, but notably the capacity to exercise. Due to the decreased
ability to ventilate independently and limited innervated skeletal muscle, 6 % of
persons with tetraplegia are unable to achieve aerobic exercise after discharge
H.W.Mercier,Ph.D.•J.A.Taylor,Ph.D.(*)
CardiovascularResearchLaboratory,SpauldingHospitalCambridge,1575CambridgeSt,
Cambridge,MA02138,USA
DepartmentofPhysicalMedicine&Rehabilitation,HarvardMedicalSchool,Cambridge,MA,
USA
e-mail:[email protected]
©TheAmericanPhysiologicalSociety2016 1
J.A.Taylor(ed.),ThePhysiologyofExerciseinSpinalCordInjury,Physiologyin
HealthandDisease,DOI10.1007/978-1-4939-6664-6_1
2 H.W.MercierandJ.A.Taylor
(National Spinal Cord Injury Statistical Center 2015). Apart from this small per-
centage, research has documented that exercise can result in notable training
adaptations and clearly protects against risk ofdeath and disease, and reduces the
limits that SCI imposes on the body (Huonker et al. 1996; Washburn and Figoni
1998;Knutssonetal.1973).AsphysiologicalchangesuniquetoSCIbecomebetter
understood, innovative technological solutions for exercise interventions and tai-
lored methods for measuring the effects of training will become increasingly
available. This chapter provides an overview to the limitations on exercise physi-
ologyforthoselivingwithSCI,aswellasconsiderationsandcurrentchallengesfor
facilitatingexerciseperformance.
1.1 Motor Limitations and Potential Adaptations
AmongthephysiologicalchangesinSCImostapparentisreducedorcompleteloss
ofvolitionalmuscularcontrolbelowthelevelofinjury.Thislimitedmotorcontrol
results fromcessation, partialorcomplete,ofsupraspinalinputtothespinalcord.
There is a potential for motor recovery in the lower extremities, however the
spinal cord can generate automatic movements without conscious or volitional
control (Roy et al. 2012). Spinal circuitry “learns” what motor action (standing,
stepping)istaught andpracticed (deLeonet al.1998a,b),anditcan “forget”the
movementwhenpracticeisceased(deLeonetal.1999;Chaetal.2007).Further-
more,thereisevidencethatthespinalcircuitrycanaltermotoractionsinresponse
to the sensory input received at a given moment, even “predicting” subsequent
motor actions through central pattern generation (Roy et al. 2012; Edgerton
et al. 2004). The spinal cord demonstrates plasticity in generating motor control
when it is trained repetitively. Remarkably, even those with motor complete SCI,
viaelectricalstimulationandrepetitivetraining,canexertcontrolonlowerextrem-
itymotoractionbasedonproprioceptiveinformation(Harkemaetal.1997;Grillner
andZangger1979;Royetal.2012).Finally,pharmacologicalandepiduralstimu-
lation interventions can amplify residual descending input to facilitate motor
recovery (de Leon et al. 1998a, b). Recognizing these adaptations and spinal
circuitryresiliency,rehabilitationhasadvancedmotorfunctionrecoveryafterSCI
using assisted motor training, spinal cord epidural stimulation, and/or pharmaco-
logical agents in recent years (Roy et al. 2012). These opportunities for regaining
lower extremity motor function present even more reason to exercise and thus
prevent secondary health complications that would complicate participation in
locomotortraining.
Within6weeksofSCI,paralyzedskeletalmusclesatrophysignificantly(Gorgey
et al. 2015). They convert to fast-type muscle fibers, becoming weak and highly
fatigable(Scottetal.2006).Inadditiontolimitingexerciseperformance,thelossof
skeletal muscle mass and extreme lower limb physical inactivity in SCI induce
structuralandfunctionalchangesintheheartandcirculatorysystemwhichleadto
increased cardiovascular disease risk. There is strong evidence for the beneficial
1 ThePhysiologyofExerciseinSpinalCordInjury(SCI):AnOverviewofthe... 3
effects of functional electrical stimulation (FES) to activate larger amounts of
muscle mass and achieve the benefits of regular aerobic exercise, including mus-
cularhypertrophy(Cramerietal.2002;Gerritsetal.2001;Pollacketal.1989;Goss
et al. 1992; Deley et al. 2015; Panisset et al. 2016). Hybrid FES exercise, which
incorporates volitional contractions of the upper body in synchrony with FES to
paralyzedmuscles,alsoservesasatotalbodyexercise(Kraussetal.1993).Though
evidenceofcomparativeeffectivenessislimited,greatergainsinaerobiccapacity
have been found using hybrid FES exercise compared to upper body exercise
alone (Verellen et al. 2007). Activating the paralyzed muscles with FES during
exercisealsohasbenefitstocardiacoutputasthelowerlimbcontractionsactasa
musclepump(Davisetal.1990).Inaddition,abdominalbinding(Westetal.2012),
compressiongarments,andanti-gravitysuits(Hopmanetal.1992)canbeusedto
counteractthelackofsympatheticallymediatedvasoconstrictionthatleadtoblood
poolingininactiveandsplanchnicareas.
1.2 Cardiovascular Implications
An accelerated age-related decline in the cardiovascular system occurs after SCI
(Phillips et al. 2012; Miyatani et al. 2009), resulting in risk for cardiovascular
disease threetimesgreater than the able-bodied and risk for stroke approximately
four times greater (Cragg et al. 2013). Factors contributing to this increased
physiologicalriskforcardiovasculardiseaseincludeautonomicdysfunction,phys-
icalinactivity,andpoormetabolicprofile.Exercisecaninducecardiacremodeling
which diminishes the functional and structural deficits after SCI (Brown and
Weaver2011;Gibbonsetal.2016).Moreover,arterialcrosssectionalareaislarger
among athletes with paraplegia compared to those who are sedentary (Huonker
et al. 1998). In fact, increases in arterial diameter have been noted after just two
weeksofFEScyclingexercise(Thijssenetal.2006)andarterialwallstiffnessmay
bereversedbyexercise(deGrootetal.2005).
Autonomic dysfunction after SCI produces an unstable cardiovascular system
and diminished blood pressure and heart rate responses to exercise. Low resting
bloodpressureandorthostatichypotensionarerelatedtoimpairedcerebrovascular
and cognitive function, syncope, fatigue, and nausea (Phillips et al. 2014a, b;
Claydon, Steeves et al. 2006). Though the symptoms are not distinct from those
inablebodiedpersons(Cleophasetal.1986;FrisbieandSteele1997;Sclaterand
Alagiakrishnan2004),orthostatichypotensionmaylimitthepositionspossiblefor
exerciseinpersonswithSCI.Incontrast,autonomicdysreflexiaoccursinresponse
to noxious afferent stimuli below the level of lesion, such as bowel or bladder
distention, tight clothing, pressure ulcers, or even standard therapeutic electrical
stimulation, and can lead to dangerously high blood pressure. Exercise has been
shown tobeasafe therapeuticapproach for attenuating the severity of autonomic
dysreflexia(DiCarloetal.1994;Halliwill2001),thoughinterestingly,athleteswith