Br J Sports Med 2013 Sherrington 730 1
2
8/12/2019 Br J Sports Med 2013 Sherrington 730 1 http://slidepdf.com/reader/full/br-j-sports-med-2013-sherrington-730-1 1/2 Why does exercise reduce falls in older people? Unrecognised contributions to motor control and cognition? Catherine Sherrington, Nicholas Henschke Falls in older people are a major public health problem and there is clear evidence that well-designed exercise interventions can prevent falls. 1 2 Over 100 randomised trials 1 of interventions to prevent falls have been undertaken, but more needs to be understood about the mechanisms for effects of interventions, about appropriate interventions to older people with differ- ent risk factors for falls, and about population-wide implementation of interventions. Liu-Ambrose et al 3 propose that exer- cise may prevent falls due to its impact on cognitive function, speci cally executive functions and functional plasticity. There is mounting evidence about the role of cognitive factors in falls and about the impact of exercise on cognition. Central and peripheral neurological changes are also key to exercise-related improvements in strength and balance. BENEFITS OF RESISTANCE TRAINING NOT LIMITED TO MUSCLE HYPERTROPHY The scientic literature concerning mechanisms underlying strength increases through resistance training has focused largely on the role of muscle mass. However, it is increasingly recognised that the gains in strength are due to a combin- ation of both morphological and neuro- logical factors. 4 5 The primary morphological adaptations are an increase in the cross-sectional area of the whole muscle and individual muscle bres. Neurological adaptations are essentially changes in coordination and learning that facilitate improved recruitment and activa- tion of the involved muscles during a spe- cic strength task. Strength gains following resistance train- ing do not parallel muscular hypertrophy, especially in the early phase of training. 6 The early gain in strength is often attributed to adaptations in the neural acti- vation of muscles, with modi cations occurring in both intramuscular and inter- muscular coordination. Such adaptations may include decreased antagonist coactiva- tion, 7 improved coordination of synergist muscles 8 and increased neural drive to agonist muscles resulting in the recruitment of additional motor units. 9 There is also growing evidence of more central neuro- logical adaptations as a result of resistance training. The specicity of strength gains to the performed resistance training indicates a process of motor learning, which has been shown to be related to cortical reorganisation. 5 In addition, there is evi- dence that training of one limb causes strength increases in the contralateral untrained limb. 10 This ‘crossover’ effect is often considered to be a result of central adaptations to resistance training. In some muscles, imagined contractions also appear to increase strength by inducing purely central nervous system adaptations. 5 The loss of muscle mass with progres- sing age may limit the bene ts from resist- ance training that can be achieved by muscle hypertrophy. It is possible that the primary means by which benets to func- tional tasks will be derived is through neuromuscular adaptations to resistance training. 6 The specic neural adaptations experienced by older adults and the mechanisms by which these changes occur will determine to what extent such changes benet the performance of move- ments other than the training exercises. For exercise to have an impact on falls we require effects on movements other than the training exercises. Several exercise intervention pro- grammes shown to prevent falls 11 12 state that they contain ‘strengthening’ exercise yet do not explicitly use the principles of muscle overload traditionally associated with resistance training interventions and appear to use weights that would be too light to have an overload effect for many participants. The impact of the se approaches to exercise on falls despite the lack of focus on muscle overload may suggest a greater role of central and per- ipheral neurological factors rather than morphological muscle adaptations. ‘BALANCE’ IS REALLY MOTOR CONTROL Many exercise interventions designed to prevent falls target balance. The term ‘balance ’ means different things to differ- ent people but most researchers now favour a broad denition of balance. For example, the Cochrane review of exercise interventions to improve balance 13 uses a denition based on the one proposed by Winter that ‘balance is the ability to stay upright and steady when stationary and during movement … the ability to main- tain the projection of the body ’s centre of mass (CoM) within manageable limits of the base of support, as in standing or sitting, or in transit to a new base of support, as in walking ’. Therefore, balance is a key aspect of the performance of all daily tasks and we cannot separate the measurement and training of balance from the measurement and training of daily task performance. Balance requires the appropriate timing and activation (ie, coordination) of many muscles, so relies on central and peripheral neurological function. Improved balance with exercise is probably as a result of central and per- ipheral neurological adaptation. TASK SPECIFICITY PROVIDES GREATER BENEFITS As it seems that both strength and balance are closely linked to task performance, strategies to improve them should involve practice of tasks relevant to daily activities. Greater bene ts are possible for people with impaired mobility when exercise is relevant to daily tasks. We found standing up ability to be enhanced in rehabilitation inpatients when strength training was con- ducted in weight-bearing rather than seated positions 14 and a greater impact on balance of standing exercise rather than seated exer- cise in older people who have recently been in hospital. 15 If the primary aim of an exercise regimen is the prevention of falls, exer- cises should be relevant to fall avoidance that is, to maintaining balance for differ- ent tasks involving different body postures with a different base of support. The exer- cises that make up the Otago Exercise Program 11 challenge balance in different positions (eg, tandem stance and walk, sideways walking). They also target muscles needed for maintenance of the upright postures (eg, extensor muscle acti- vation by sit-to-stand practice and calf muscle activation during heel raises). Liu-Ambrose et al 3 have highlighted the role of executive functions in falls and response to exercise. We suggest that central Musculoskeletal Division, The George Institute for Global Health, University of Sydney, Sydney, New South Wales, Australia Correspondence to A/Professor Catherine Sherrington, Musculoskeletal Division, The George Institute for Global Health, PO Box M201, Missenden Road, Sydney, NSW 2050, Australia;csherrington@ georgeinstitute.org.au 730 Br J Sports Med August 2013 Vol 47 No 12 Editorial
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Transcript of Br J Sports Med 2013 Sherrington 730 1
8122019 Br J Sports Med 2013 Sherrington 730 1
httpslidepdfcomreaderfullbr-j-sports-med-2013-sherrington-730-1 12
Why does exercise reduce falls in olderpeople Unrecognised contributions tomotor control and cognition
Catherine Sherrington Nicholas Henschke
Falls in older people are a major publichealth problem and there is clear evidencethat well-designed exercise interventionscan prevent falls1 2 Over 100 randomisedtrials1 of interventions to prevent fallshave been undertaken but more needs tobe understood about the mechanisms foreffects of interventions about appropriateinterventions to older people with differ-ent risk factors for falls and aboutpopulation-wide implementation of interventions
Liu-Ambrose et al3
propose that exer-cise may prevent falls due to its impact oncognitive function speci1047297cally executivefunctions and functional plasticity Thereis mounting evidence about the role of cognitive factors in falls and about theimpact of exercise on cognition
Central and peripheral neurologicalchanges are also key to exercise-relatedimprovements in strength and balance
BENEFITS OF RESISTANCE TRAININGNOT LIMITED TO MUSCLE
HYPERTROPHYThe scienti1047297c literature concerningmechanisms underlying strength increasesthrough resistance training has focusedlargely on the role of muscle massHowever it is increasingly recognised thatthe gains in strength are due to a combin-ation of both morphological and neuro-logical factors4 5 The primarymorphological adaptations are an increasein the cross-sectional area of the wholemuscle and individual muscle 1047297bresNeurological adaptations are essentiallychanges in coordination and learning that
facilitate improved recruitment and activa-tion of the involved muscles during a spe-ci1047297c strength task
Strength gains following resistance train-ing do not parallel muscular hypertrophyespecially in the early phase of training6
The early gain in strength is often
attributed to adaptations in the neural acti-vation of muscles with modi1047297cationsoccurring in both intramuscular and inter-muscular coordination Such adaptationsmay include decreased antagonist coactiva-tion7 improved coordination of synergistmuscles8 and increased neural drive toagonist muscles resulting in the recruitmentof additional motor units9 There is alsogrowing evidence of more central neuro-logical adaptations as a result of resistancetraining The speci1047297city of strength gains to
the performed resistance training indicatesa process of motor learning which hasbeen shown to be related to corticalreorganisation5 In addition there is evi-dence that training of one limb causesstrength increases in the contralateraluntrained limb10 This lsquocrossoverrsquo effect isoften considered to be a result of centraladaptations to resistance training In somemuscles imagined contractions also appearto increase strength by inducing purelycentral nervous system adaptations5
The loss of muscle mass with progres-sing age may limit the bene1047297ts from resist-ance training that can be achieved bymuscle hypertrophy It is possible that theprimary means by which bene1047297ts to func-tional tasks will be derived is throughneuromuscular adaptations to resistancetraining6 The speci1047297c neural adaptationsexperienced by older adults and themechanisms by which these changes occurwill determine to what extent suchchanges bene1047297t the performance of move-ments other than the training exercisesFor exercise to have an impact on falls werequire effects on movements other than
the training exercisesSeveral exercise intervention pro-
grammes shown to prevent falls11 12 statethat they contain lsquostrengtheningrsquo exerciseyet do not explicitly use the principles of muscle overload traditionally associatedwith resistance training interventions andappear to use weights that would be toolight to have an overload effect for manyparticipants The impact of theseapproaches to exercise on falls despite thelack of focus on muscle overload maysuggest a greater role of central and per-ipheral neurological factors rather thanmorphological muscle adaptations
lsquoBALANCErsquo IS REALLY MOTORCONTROLMany exercise interventions designed toprevent falls target balance The termlsquobalancersquo means different things to differ-ent people but most researchers nowfavour a broad de1047297nition of balance Forexample the Cochrane review of exercise
interventions to improve balance13
uses ade1047297nition based on the one proposed byWinter that lsquobalance is the ability to stayupright and steady when stationary andduring movement hellip the ability to main-tain the projection of the bodyrsquos centre of mass (CoM) within manageable limits of the base of support as in standing orsitting or in transit to a new base of support as in walkingrsquo Thereforebalance is a key aspect of the performanceof all daily tasks and we cannot separatethe measurement and training of balancefrom the measurement and training of daily task performance Balance requiresthe appropriate timing and activation (iecoordination) of many muscles so relieson central and peripheral neurologicalfunction Improved balance with exerciseis probably as a result of central and per-ipheral neurological adaptation
TASK SPECIFICITY PROVIDESGREATER BENEFITS
As it seems that both strength and balanceare closely linked to task performance
strategies to improve them should involvepractice of tasks relevant to daily activitiesGreater bene1047297ts are possible for peoplewith impaired mobility when exercise isrelevant to daily tasks We found standingup ability to be enhanced in rehabilitationinpatients when strength training was con-ducted in weight-bearing rather than seatedpositions14 and a greater impact on balanceof standing exercise rather than seated exer-cise in older people who have recently beenin hospital15
If the primary aim of an exerciseregimen is the prevention of falls exer-cises should be relevant to fall avoidancethat is to maintaining balance for differ-ent tasks involving different body postureswith a different base of support The exer-cises that make up the Otago ExerciseProgram11 challenge balance in differentpositions (eg tandem stance and walksideways walking) They also targetmuscles needed for maintenance of theupright postures (eg extensor muscle acti-vation by sit-to-stand practice and calf muscle activation during heel raises)
Liu-Ambrose et al3 have highlighted the
role of executive functions in falls andresponse to exercise We suggest that central
Musculoskeletal Division The George Institute forGlobal Health University of Sydney Sydney New SouthWales Australia
Correspondence to AProfessor CatherineSherrington Musculoskeletal Division The GeorgeInstitute for Global Health PO Box M201 Missenden
Road Sydney NSW 2050 Australiacsherringtongeorgeinstituteorgau
730 Br J Sports Med August 2013 Vol 47 No 12
Editorial
8122019 Br J Sports Med 2013 Sherrington 730 1
httpslidepdfcomreaderfullbr-j-sports-med-2013-sherrington-730-1 22
and peripheral neurological adaptations area crucial part of strength and balanceenhancement and should not be forgottenwhen trying to understand the mechanismsfor the effect of exercise interventions
Competing interests None
Provenance and peer review Not commissioned
externally peer reviewedTo cite Sherrington C Henschke N Br J Sports Med 201347730ndash731
Received 17 April 2012Accepted 30 May 2012Published Online First 19 July 2012
Br J Sports Med 201347730ndash731doi101136bjsports-2012-091295
REFERENCES1 Gillespie LD Robertson MC Gillespie WJ et al
Interventions for preventing falls in elderly peopleCochrane Database Syst Rev 20092CD000340 doi10100214651858CD000340pub2
2 Sherrington C Tiedemann A Fairhall N et al
Exercise to prevent falls in older adults an updated
meta-analysis and best practice recommendationsNSW Public Health Bull 20112278ndash83
3 Liu-Ambrose T Nagamatsu L Hsu C et al Emergingconcept lsquoCentral Bene1047297t Modelrsquo of exercise in fallsprevention Br J Sports Med 201347115ndash7
4 Folland JP Williams AG The adaptations to strengthtraining morphological and neurologicalcontributions to increased strength Sports Med 200737145ndash68
5 Gabriel DA Kamen G Frost G Neural adaptations to
resistive exercise mechanisms and recommendationsfor training practices Sports Med 200636133ndash49
6 Barry BK Carson RG The consequences of resistancetraining for movement control in older adults JGerontol 200459730ndash54
7 Carolan B Cafarelli E Adaptations in coactivationafter isometric resistance training J Appl Physiol 199273911ndash17
8 Rutherford OM Jones DA The role of learning andcoordination in strength training Eur J Appl Physiol Occup Physiol 198655100ndash5
9 Akima H Takahashi H Kuno SY et al Early phaseadaptations of muscle use and strength toisokinetic training Med Sci Sports Exerc 199931588ndash94
10 Carroll TJ Herbert RD Munn J et al Contralateral
effects of unilateral strength training evidence and
possible mechanisms J Appl Physiol 20061011514ndash22
11 Robertson MC Campbell AJ Gardner MM et al Preventing injuries in older people by preventingfalls a meta-analysis of individual-level data J AmGeriatr Soc 200250905ndash11
12 Clemson L Cumming RG Kendig H et al Theeffectiveness of a community-based program forreducing the incidence of falls in the elderly arandomized trial J Am Geriatr Soc
2004521487ndash9413 Howe TE Rochester L Neil F et al Exercise for
improving balance in older people CochraneDatabase Syst Rev 201111CD004963 doi10100214651858CD004963pub3
14 Olivetti L Schurr K Sherrington C et al A novelweight-bearing strengthening program duringrehabilitation of older people is feasible and improvesstanding up more than a nonweight-bearingstrengthening program a randomised trial Aust JPhysiother 200753147ndash53
15 Vogler C Sherrington C Ogle S et al Reducingfalls risk in older people discharged fromhospital a randomised controlled trial comparingseated limb exercises weight-bearing exercises andsocial visits Arch Phys Med Rehabil 200990
1317ndash
24
Br J Sports Med August 2013 Vol 47 No 12 731
Editorial
8122019 Br J Sports Med 2013 Sherrington 730 1
httpslidepdfcomreaderfullbr-j-sports-med-2013-sherrington-730-1 22
and peripheral neurological adaptations area crucial part of strength and balanceenhancement and should not be forgottenwhen trying to understand the mechanismsfor the effect of exercise interventions
Competing interests None
Provenance and peer review Not commissioned
externally peer reviewedTo cite Sherrington C Henschke N Br J Sports Med 201347730ndash731
Received 17 April 2012Accepted 30 May 2012Published Online First 19 July 2012
Br J Sports Med 201347730ndash731doi101136bjsports-2012-091295
REFERENCES1 Gillespie LD Robertson MC Gillespie WJ et al
Interventions for preventing falls in elderly peopleCochrane Database Syst Rev 20092CD000340 doi10100214651858CD000340pub2
2 Sherrington C Tiedemann A Fairhall N et al
Exercise to prevent falls in older adults an updated
meta-analysis and best practice recommendationsNSW Public Health Bull 20112278ndash83
3 Liu-Ambrose T Nagamatsu L Hsu C et al Emergingconcept lsquoCentral Bene1047297t Modelrsquo of exercise in fallsprevention Br J Sports Med 201347115ndash7
4 Folland JP Williams AG The adaptations to strengthtraining morphological and neurologicalcontributions to increased strength Sports Med 200737145ndash68
5 Gabriel DA Kamen G Frost G Neural adaptations to
resistive exercise mechanisms and recommendationsfor training practices Sports Med 200636133ndash49
6 Barry BK Carson RG The consequences of resistancetraining for movement control in older adults JGerontol 200459730ndash54
7 Carolan B Cafarelli E Adaptations in coactivationafter isometric resistance training J Appl Physiol 199273911ndash17
8 Rutherford OM Jones DA The role of learning andcoordination in strength training Eur J Appl Physiol Occup Physiol 198655100ndash5
9 Akima H Takahashi H Kuno SY et al Early phaseadaptations of muscle use and strength toisokinetic training Med Sci Sports Exerc 199931588ndash94
10 Carroll TJ Herbert RD Munn J et al Contralateral
effects of unilateral strength training evidence and
possible mechanisms J Appl Physiol 20061011514ndash22
11 Robertson MC Campbell AJ Gardner MM et al Preventing injuries in older people by preventingfalls a meta-analysis of individual-level data J AmGeriatr Soc 200250905ndash11
12 Clemson L Cumming RG Kendig H et al Theeffectiveness of a community-based program forreducing the incidence of falls in the elderly arandomized trial J Am Geriatr Soc
2004521487ndash9413 Howe TE Rochester L Neil F et al Exercise for
improving balance in older people CochraneDatabase Syst Rev 201111CD004963 doi10100214651858CD004963pub3
14 Olivetti L Schurr K Sherrington C et al A novelweight-bearing strengthening program duringrehabilitation of older people is feasible and improvesstanding up more than a nonweight-bearingstrengthening program a randomised trial Aust JPhysiother 200753147ndash53
15 Vogler C Sherrington C Ogle S et al Reducingfalls risk in older people discharged fromhospital a randomised controlled trial comparingseated limb exercises weight-bearing exercises andsocial visits Arch Phys Med Rehabil 200990
1317ndash
24
Br J Sports Med August 2013 Vol 47 No 12 731
Editorial
