Extrinsic feedback and management of low back pain: A critical review of the literature

Abstract

Effective intervention for low back pain (LBP) can include feedback in one form or other. Although extrinsic feedback (EF) can be provided in a number of ways, most research has not considered how different EF characteristics (e.g. timing and content) influence treatment outcomes. A systematic search related to feedback and LBP was performed on relevant electronic databases. This narrative review aims to describe the forms of feedback provision in the literature regarding management of LBP, and to discuss these in light of previously recommended principles for the use of extrinsic feedback. The present review found support for the provision of EF that focuses on content characteristics including program feedback, summary results feedback, and external focus of attention. Temporal characteristics should enhance the use of intermittent or self-selected feedback. The literature does not support the provision of concurrent or constant EF. As much of the literature related to EF in the management of LBP has not considered content and timing characteristics we have identified future research directions that will clarify the use of content and timing characteristics of EF relative to the management of LBP.

Full text

Systematic Review
Extrinsic feedback and management of low back pain: A critical review of the
literature
Daniel Cury Ribeiro
a
,
*
, Gisela Sole
a
, J. Haxby Abbott
b
, Stephan Milosavljevic
a
a
Centre for Physiotherapy Research, School of Physiotherapy, University of Otago, 325 Great King Street, Dunedin 9016, New Zealand
b
Orthopaedic Surgery eMedical and Surgical Sciences, Dunedin School of Medicine, University of Otago, Dunedin, 913, New Zealand
article info
Article history:
Received 5 May 2010
Received in revised form
22 November 2010
Accepted 13 December 2010
Keywords:
Feedback
Rehabilitative ultrasound imaging
Back pain
Exercise therapy
abstract
Effective intervention for low back pain (LBP) can include feedback in one form or other. Although
extrinsic feedback (EF) can be provided in a number of ways, most research has not considered how
different EF characteristics (e.g. timing and content) influence treatment outcomes. A systematic search
related to feedback and LBP was performed on relevant electronic databases. This narrative review aims
to describe the forms of feedback provision in the literature regarding management of LBP, and to discuss
these in light of previously recommended principles for the use of extrinsic feedback. The present review
found support for the provision of EF that focuses on content characteristics including program feedback,
summary results feedback, and external focus of attention. Temporal characteristics should enhance the
use of intermittent or self-selected feedback. The literature does not support the provision of concurrent
or constant EF. As much of the literature related to EF in the management of LBP has not considered
content and timing characteristics we have identified future research directions that will clarify the use
of content and timing characteristics of EF relative to the management of LBP.
Ó2010 Elsevier Ltd. All rights reserved.
1. Introduction
Motor control feedback can be defined as information provided
by different sensory receptors as a consequence of a movement
(Shumway-Cook and Woollacott, 2007). Such feedback informs
about the effect of actions, and is designed to help improve the
quality of adaptive responses (Schmidt and Wrisberg, 2008).
Information provided by the sensory system is called intrinsic
feedback, while the information provided via an external source
(another person or instrument) can be described as extrinsic feed-
back (EF) (or, augmented feedback) (Schmidt and Wrisberg, 2008).
Depending on the type of task, intrinsic feedback provides suffi-
cient information to help execute or improve task performance.
Nonetheless, there can be situations where motor improvements
are very difficult to achieve without the support of EF (Guadagnoli
et al., 1996), such as in individuals whose intrinsic feedback is
impaired, in which case (re)learning of a task can be complex
(Herbert et al., 2008).
EF has been used by physiotherapists in the management of
patients with specific neuro-musculoskeletal conditions (Dozza
et al., 2005; Magnusson et al., 2008; Durham et al., 2009), such as
low back pain (LBP) and Parkinson disease. Different EF devices
include verbal feedback (Durham et al., 2009), visual feedback for
postural control and weight bearing symmetry (Brumagne et al.,
2008a; Hlavackova et al., 2009), audio feedback (Dozza et al.,
2005; Wong and Wong, 2008), and rehabilitative ultrasound
imaging feedback (Teyhen et al., 2005). EF is argued to enhance:
a) central nervous system facilitation of optimal sensory-motor
loops; b) patient awareness, confidence and volitional control over
specific physiological processes; c) motivation; and d) reinforce-
ment for repetition of successful actions (Huang et al., 2006;
Schmidt and Wrisberg, 2008).
Patients with LBP are thought to have an impaired intrinsic
feedback system (Descarreaux et al., 2005; Panjabi, 2006;
Brumagne et al., 2008b) with an alteration in muscular response
(Sterling et al., 2001; Jacobs et al., 2009). The adverse alteration of
proprioception is thought to play an important role in the main-
tenance of symptoms and motor impairments (O’Sullivan et al.,
2003; Dolan and Green, 2006; Panjabi, 2006). The intrinsic feed-
back system can be altered due to disrupted paraspinal muscle
spindle input, as well as, imprecise central processing, causing
lumbar position sense deficits (Brumagne et al., 2000). In addition,
partial ruptures of spinal ligaments leads to imprecise feedback
input to the central neural system, causing reduced postural
awareness and altered motor recruitment patterns (Panjabi, 2006).
*Corresponding author. University of Otago, Centre for Physiotherapy Research,
School of Physiotherapy, University of Otago, PO Box 56, Dunedin 9015, New Zea-
land. Tel.: þ64 3 479 5422, fax: þ64 3 479 8414.
E-mail address: daniel.cury.ribeiro@gmail.com (D.C. Ribeiro).
Contents lists available at ScienceDirect
Manual Therapy
journal homepage: www.elsevier.com/math
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doi:10.1016/j.math.2010.12.001
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Examples reported in the literature are the delayed contraction of
transversus abdominis muscle in subjects with LBP (Hodges, 1999),
the localized atrophy and reduced capacity of actively recruit the
lumbar multifidus muscle (Wallwork et al., 2009), as well as,
increased spinal co-contraction (Newton-John et al., 1995; Marras
et al., 2000) which increases spinal load (Marras et al., 2000). It is
considered that EF is a useful procedure that facilitates or augments
the information provided by the somato-sensory system (Henry
and Teyhen, 2007).
The successful provision of EF depends on the selection of
different features (Park et al., 2000; van Vliet and Wulf, 2006).
Characteristics of feedback (e.g. when to provide EF, what type of
information to be delivered) during motor learning have been
discussed in depth (Newell, 1976;Hebert and Landin, 1994;
McNevin et al., 1994;Smith et al., 1997; Park et al., 2000;
Guadagnoli and Lee, 2004) and its implications for rehabilitation
have been presented (Winstein and Knecht, 1990; Winstein, 1991;
McNevin et al., 2000). These characteristics have been recently
investigated during rehabilitation procedures for specific neuro-
muscular dysfunctions such as stroke (van Vliet and Wulf, 2006)
and LBP (Herbert et al., 2008). However, the studies investigating
the use of feedback towards managements of LBP are still limited
(Henry and Teyhen, 2007). The aim of this narrative review is to
describe the forms of feedback provision in the literature regarding
management of LBP, and to discuss these in light of previously
recommended principles for the use of EF.
2. Methods
The electronic search identified studies that have included the
use of EF on the management of LBP. The following databases were
used: Medline (1950eAugust 2010), CINAHL (1982eAugust 2010),
PsycINFO (1967eAugust 2010), Embase (1947 August 2010). Addi-
tional searches used the PEDro database, as well as searches of
rehabilitation journals including: Manual Therapy, Physiotherapy,
Physical Therapy, Archives of Physical Medicine and Rehabilitation,
Journal of Orthopaedic and Sports Physical Therapy (JOSPT). The
search strategy was developed in consultation with a faculty
librarian. The key words and the combination used for each data-
base are described in Table 1. In addition, reference lists of retrieved
articles were scanned for appropriate studies. Language restriction
was not imposed.
Studies were included if they involved a randomized control
trial of subjects, with or without LBP, exposed to a period of training
or treatment using feedback instruments (with or without the
addition of verbal or tactile feedback) that focused on motor
learning. Studies were excluded if they had any other study design,
were narrative or systematic reviews, if the focus of the study was
on behavioral feedback, or ergonomic training, or if it was not
related to motor training.
The quality scores for those studies were assessed by the PEDro
database (http://www.pedro.org.au). For studies not assessed by
the PEDro database, we report our quality assessment findings
using the PEDro instrument (http://www.pedro.org.au). Two
reviewers (DCR, JHA) independently assessed each study. Differ-
ences were resolved by consensus. A third reviewer (GS) was
available to adjudicate unresolved differences.
In order to establish the recommended principles for the use of
EF, the following textbooks were reviewed (Magill, 2003;
Shumway-Cook and Woollacott, 2007; Schmidt and Wrisberg,
2008), as were published articles related to motor learning and
control. To identify these studies, an electronic search, through the
same databases previously described, was conducted and the
following key words used were: motor learning, motor control,
feedback, extrinsic feedback, knowledge of results, and knowledge
of performance.
3. Results
A total of 311 articles were found and 17 studies met the
inclusion criteria. The identification, screening, eligibility and
inclusion processes are described in Fig. 1. Main term definitions for
content and timing characteristics of feedback provision are
described in Table 2.
Study design description, as well as, main content and timing
characteristics of EF found in the studies identified through the
electronic search are outlined in Tables 3e5, respectively. From the
17 included studies, 6 studies (Henry and Westervelt, 2005; Teyhen
et al., 2005; Van et al., 2006; Worth et al., 2007; Herbert et al., 2008;
Magnusson et al., 2008) have compared use of EF with no use of EF
in the intervention regime (Table 3); their main findings are pre-
sented in Table 6. The other 11 studies (Bush et al., 1985; Donaldson
et al., 1994; Ferreira et al., 20 07; Flor et al., 1983; Hides et al., 1996;
Newton-John et al., 1995; Niemisto et al., 2003; Nouwen, 1983;
Rasmussen-Barr et al., 2003; Stuckey et al., 1986; Vasseljen and
Fladmark, 2010) have used EF as part of treatment/motor training
management; however have not conducted a comparative effec-
tiveness study of EF. As a consequence, all comments regarding the
effectiveness of EF provision will be based on the former 6 studies.
The latter 11 studies are presented and the way EF was provided is
narratively described and compared to the recommendation
summary for EF provision. The PEDro quality assessment results are
reported in Table 3.
Before specifically describing the extracted data related to the
use of EF in the management of LBP, a summary of existing
recommendations related to EF in motor learning is presented in
two domains: content feedback and timing feedback. LBP feedback
characteristics are then reviewed and compared with this summary
of existing recommendations.
4. Recommendations for the use of EF
The provision of EF can target different sensory channels (visual,
kinesthetic, and verbal knowledge of results). Sarlegna et al. (2007)
tested how adaptive control during reaching movements was
Table 1
Results for electronic databases searches.
Database Keywords Number of studies
PsycInfo (1) Back pain;
(2) Biofeedback Training;
(3) Biofeedback;
(4) Feedback;
(5) 2 or 3 or 4;
(6) 1 and 5.
39
Embase (1) Feedback system;
(2) Low back pain;
(3) Backache;
(4) 2 or 3;
(5) 1 and 4.
182
Medline (1) Low back pain;
(2) Feedback;
(3) Feedback, Sensory;
(4) Biofeedback, Psychology;
(5) 2 or 3 or 4;
(6) 1 and 5.
34
Cinahl (1) Low back pain;
(2) Feedback;
(3) Biofeedback;
(4) Extrinsic Feedback;
(5) 2 or 3 or 4;
(6) 1 and 5.
54
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affected by different sensory channels and found there were no
differences in motor adaptation between the different feedback
groups. This study supports the concept that sensory-motor
adaptation is a multi-sensory flexible process and its efficiency
seems to be independent of a specific sensory channel (e.g. Vision,
audition, or kinesthesia) (Sarlegna et al., 2007). In spite of which
sensory channel is targeted, clinicians must therefore decide the
most effective way to provide EF for their patients.
Extrinsic feedback can be provided in two forms: knowledge of
results and knowledge of performance (Schmidt and Wrisberg,
2008). Knowledge of results informs about the outcome or
achieving the goal/target of a determined task, whereas, knowledge
of performance feedback informs about the characteristics of
a performed movement or task (Magill, 2000). The characteristics
of such EF can have positive, detrimental or null influence on the
motor learning outcomes (Wulf et al., 1994). For this reason, before
providing EF, content and timing characteristics should be carefully
selected (Butki and Hoffman, 2003; Guadagnoli and Kohl, 2001;
Ishikura, 2005).
4.1. Content characteristics
In the present review, content characteristics are considered as
features related to the focus of intervention of the EF (program or
parameter), the way EF results are provided (summarized, aver-
aged, or error magnitude ee.g. accepting some minor faults as
a successful try), and the type of focus of attention associated with
the feedback (Table 2). Skill complexity, feedback redundancy and
subject experience have an important effect on learning outcomes
from EF (Guadagnoli and Lee, 2004; Janelle et al., 1997; Park et al.,
2000). When learning a new but easy task, EF does not necessarily
result in enhancement of learning. While learning a complex task,
provision of EF seems to enhance motor performance (Fredenburg
et al., 2001). When there is sufficient intrinsic information, EF
provision will not necessarily induce better learning outcomes
(Guadagnoli et al., 1996). In this case, it is generally accepted that
the therapist should direct and assist the subject to correctly
identify and use the available intrinsic feedback information during
task execution (Schmidt and Wrisberg, 2008). The more novel the
task and less experienced the participant; the more useful EF is
likely to be (Guadagnoli et al., 1996; Guadagnoli and Lee, 2004).
4.1.1. Program and parameter feedback
Learning a new task involves the acquisition of a generalized
motor pattern followed by the refinement of specific execution
parameters (Schmidt and Wrisberg, 2008). Different types of
instruction feedback can be used to improve motor learning
during these two phases. Program feedback provides information
regarding the general movement pattern, while parameter feed-
back provides information of a specific component of the entire
movement pattern (Schmidt and Wrisberg, 2008). Both forms of
feedback can be provided prescriptively or descriptively. The
former describes errors and suggests how to correct them while
the latter only describes the errors (Schmidt and Wrisberg, 2008).
Records identified through
database searching
(n = 309)
Additional records identified
through other sources
(n = 2)
Records after duplicates removed
(n = 283)
Records screened
(n = 283)
Records excluded (n = 264):
- Not RCT, narrative
reviews, guidelines,
unrelated to motor training
of low back muscles, focus
on behavioral feedback, and
focus on lifting ergonomic
training feedback.
Full-text articles
assessed for eligibility
(n = 19)
Full-text articles excluded
with reasons (n= 2):
- Included patients with
other musculoskeletal
disorders (n = 1)
- Related to psychological
behavioural feedback
(n = 1)
Studies included in
qualitative synthesis
(n = 17)
Fig. 1. Selection process.
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Better results are often obtained when prescriptive feedback is
provided.
4.1.2. Amount of information during feedback provision
The quantity and precision of EF can interfere in the learning
process (Guadagnoli et al., 1996;Ishikura, 2005). Summary feed-
back, which provides information after a specific number of trials,
has shown to be superior, when compared to EF provided after
every trial (Gable et al., 1991). Average feedback provides mean
values (mean error or performance score) of a group of trials (Wulf
and Schmidt, 1996), it is considered to deteriorate movement
parameter learning (Wulf and Schmidt, 1996), but to be superior to
every trial EF. During every trial feedback, subjects ignore intrinsic
feedback information and become excessively dependent on EF
(Ranganathan and Newell, 2009a; Salmoni et al., 1984).
4.1.3. Performance bandwidth (error magnitude)
Another important issue is to determine the error magnitude
(performance bandwidth) that should be followed by feedback
(Butler et al., 1996; Lai and Shea, 1999; Smith et al., 1997). For
example, isolated contraction for lumbar multifidus can be
considered as successful when no pelvic tilt is performed
concomitantly, and multifidus muscle thickening can be visualized
on the rehabilitative ultrasound imaging screen (Herbert et al.,
2008). In this example, the physiotherapist might consider
a performance as successful even when small amount of pelvic tilt
movement occur simultaneously to multifidus muscle contraction.
Some studies support the idea that changing the bandwidth size
during motor task trials does not alter motor outcomes (Goodwin
and Meeuwsen, 1995; Lai and Shea, 1999). Conversely, Smith
et al. (1997) found that a larger bandwidth (10%, when compared
to 0 and 5%) has been associated with better retention outcomes.
The use of bandwidth for EF provision enhances motor learning if
qualitative knowledge of results feedback is provided when motor
outcome is included within the bandwidth (Butler et al., 1996). In
other words, subjects need to be aware that non-provision of EF
means performance was considered either correct or within a pre-
determined error tolerance (Butler et al., 1996).
4.1.4. Focus of attention
EF can be applied in a form that drives learner’s attention to
body movement characteristics (internal focus of attention) or to
the effect of the movement (external focus of attention) (Wulf et al.,
2002). Better motor learning outcomes are related to the use of
external focus of attention (Shea and Wulf, 1999; McNevin et al.,
2000; Wulf et al., 2009). The reasons for this are unclear,
however, it seems that attempts to control the movement itself
would interfere in automatic motor control processes and, conse-
quently, lead to deteriorated outcomes (McNevin et al., 2000). The
use of an external focus of attention likely facilitates or sustains
automatic pathways of motor control and improve motor perfor-
mance (Wulf et al., 2009).
4.2. Timing characteristics
The excessive use of EF can lead to dependency and, conse-
quently, promote detrimental or null effects on learning process
(Winstein and Schmidt, 1990; Park et al., 20 00;Butki and Hoffman,
2003). Concurrent or terminal (immediate or delayed) EF, as well
as, the frequency of EF are critical features of application during
motor learning (Magill, 2003; Schmidt and Wrisberg, 2008). EF can
be provided during every trial (constant), concurrent to the task
execution, immediately after task execution or, after a period of
time following the end of the task (delayed).
4.2.1. Concurrent and terminal feedback provision
Whether to provide EF concurrent to or after task execution is
a decision to be made by the physiotherapist. Published literature
does not support the use of concurrent EF, unless there is impaired
intrinsic feedback or insufficient information intrinsic to the task
(Park et al., 2000; Magill, 2003; Ranganathan and Newell, 2009a).
This might be the case for LBP patients, who were shown to have
impaired intrinsic feedback (Newcomer et al., 2000). Otherwise,
concurrent EF has a strong negative guidance effect (Winstein et al.,
1996; Schmidt and Wulf, 1997). One possible reason might be
related to EF obliterating the use of intrinsic feedback. Learners
become dependent on EF during the acquisition phase and,
consequently, when EF is removed, subjects are not able to perform
the task correctly (Anderson et al., 2005). Even though concurrent
visual feedback has been shown to be detrimental (Wulf and
Schmidt, 1997), the provision of concurrent audio feedback is
beneficial for motor learning (Konttinen et al., 2004). Concurrent
visual feedback appears to induce a different neural pathway when
compared to the execution of atask without visual EF. However, the
reasons for the better retention results from learning with audio
feedback are unclear.
Delayed EF improves motor learning outcomes (Magill, 2003;
Anderson et al., 2005). It is possible that, by delaying the feedback
provision for a few seconds or minutes after movement execution,
subjects have time to better explore their intrinsic feedback and
relate it to the motor outcome. When EF is provided, they can then
compare the intrinsic feedback information to that provided by the
EF (Anderson et al., 2005). However, the optimal delay interval for
providing EF has yet to be determined (Magill, 2003).
4.2.2. Frequency of feedback provision
Additionally, providing EF after every trial (100% EF) appears to
deteriorate motor learning, when compared to intermittent EF (e.g.
Table 2
Main term definitions for content and timing characteristics.
Content characteristics
Program feedback Feedback related to the
general pattern of movement.
Parameter feedback Feedback related to a specific
component (part) of the whole
movement pattern.
Summary feedback Feedback is pooled and
provided after a specific
number of trials.
Average feedback Feedback provided refers to mean
values (mean error or performance
score) of a group of trials.
Bandwidth
(error magnitude)
The amount of error that is
considered to distinguish between
successful and unsuccessful trials.
Internal focus of attention Feedback drives learner’s attention
to body movement characteristics.
External focus of attention Feedback drives learner’s attention
to the effect of the movement.
Timing characteristics
Concurrent feedback Feedback is provided simultaneous
to task execution.
Terminal feedback Feedback is provided after
task execution.
Immediate Feedback is provided immediately
after task execution;
Delayed Feedback provision is delayed
after the end of the task execution.
Frequency
Constant Feedback is provided at every trial.
Reduced Feedback is provided for a fraction
of trials (e.g. 30%).
Self controlled Feedback provision depends on
learner’s decision.
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50%, 20% or 10% EF) (Salmoni et al., 1984; Winstein and Schmidt,
1990; Weeks and Kordus, 1998; Park et al., 2000). Weeks and
Kordus (1998) found that uninjured learners, who received 33%
relative frequency of knowledge of performance feedback, per-
formed better when compared to 100% relative EF during a soccer
throw-in task. The authors suggested that reduced frequency
Table 3
Study description.
Author (Year) Population Intervention Nature of EF
(KP or KR)
Type
of EF
Instrument/
Principle
PEDro
Score
Vasseljen and Fladmark,
2010
109 chronic LBP
patients
8-week intervention (8 sessions) G1:
Low load exercise (stabilization focused on
transverses abdominis) with USI ;G2:
High load exercise; G3: General exercise.
KP Visual USI 6/10
a
Magnusson et al. (2008) 26 LBP patients 5-week intervention (10 sessions) G1:
Conventional physiotherapy; G2:
Conventional
physiotherapy + biofeedback
KP Visual, auditory,
success rates, reports
Postural 3/10
b
Herbert et al. (2008) 30 healthy
participants
4-week intervention (8 sessions):
multifidus muscle exercise G1: constant
USI;
G2: variable USI
KR (verbal)
KP (visual)
Visual
Verbal
USI 5/10
a
Ferreira et al. (2007) 240 chronic
LBP patients
8-week intervention (12 sessions) G1:
General exercise; G2: Motor control
exercise + USI; G3: Manipulative therapy
KP Visual USI 8/10
b
Worth et al. (2007) 19 LBP patients Teaching abdominal hollowing exercise
and retention test after 4 days. G1verbal
and palpatory feedback; G2: USI
KP Visual USI 5/10
b
Van et al. (2006) 25 healthy subjects Teaching isometric contraction of
multifidus
muscle. G1: Knowledge of results; G2:
Knowledge of results and performance.
KR (amount of
increase
in muscle thickness)
and
KP (visual observation
of muscle contraction)
Visual, report USI 4/10
a
Teyhen et al. (2005) 30 LBP patients G1: lumbar stabilization exercise; G2:
lumbar stabilization exercise + USI; Both
groups received 1 session followed
short-term re-assessment (3 min after
session).
Retention test was carried out after 4 days
(all patients received home exercises).
KP Visual USI 7/10
b
Henry and Westervelt
(2005)
48 healthy
participants
Teaching abdominal hollowing exercise
and
retention test after 4 days. G1: minimal
verbal
feedback; G2: verbal and palpatory
feedback;
G3: verbal, palpatory and USI
KP Verbal, tactile
and visual
USI 6/10
a
Rasmussen-Barr et al.
(2003)
47 LBP patients 6-week treatment (one session/week).
G1: Stabilizing group (PBU);
G2: Manual treatment group
KP Pressure PBU 5/10
b
Niemisto et al. (2003) 240 LBP patients 4-week intervention (one session/week).
G1: Manipulation and stabilizing exercise
(abdominal drawing-in maneuver);
G2: Physician consultation
KP and KR Pressure, visual and
tactile
PBU 8/10
b
Hides et al. (1996) 39 LBP patients 4-week intervention G1: Medical
management; G2: Medical management
and stabilization exercises
KP Visual USI 7/10
b
Newton-John et al. (1995) 44 LBP patients 8-week intervention (2x/week).
G1: Cognitive behavior therapy;
G2: EMG Biofeedback; G3: Wait list control
KP Not adressed EMG 3/10
b
Donaldson et al. (1994) 36 chronic LBP G1: EMG Biofeedback, G2: Relaxation;
G3: Education
Not adressed Not adressed EMG 5/10
b
Stuckey et al. (1986) 24 chronic LBP 8 sessions (45 min each) G1: EMG
feedback;
G2: Relaxation training; G3: Placebo
condition
KP Visual and auditory EMG 4/10
b
Bush et al. (1985) 72 chronic LBP 8 sessions (period of intervention unclear)
G1: Paraspinal EMG feedback; G2: Placebo;
G3: No intervention
KP Auditory EMG 4/10
b
Nouwen (1983) 20 LBP patients 3-week intervention (5x/week). G1: EMG
Biofeedback; G2: Wait list control
KP Visual and auditory EMG 5/10
b
Flor et al. (1983) 24 chronic LBP G1: EMG feedback; G2: Pseudo therapy;
G3: Conventional medical treatment
KP Auditory EMG 4/10
b
G1: group 1; G2: group 2; G3: group 3; EF ¼extrinsic feedback; KP ¼knowledge of performance; KR ¼knowledge of results; PBU ¼pressure biofeedback unit; USI -
¼ultrasound imaging; EMG ¼electromyopgrahic feedback.
a
PEDro score assessed by the authors.
b
PEDro score reported from www.pedro.org.au.
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eliminates learner’s dependence on the provision of EF (Weeks and
Kordus, 1998). A possible explanation for reduced retention with
100% EF is that EF is a guide for motor execution and learners
cannot guide themselves appropriately by task-intrinsic feedback
when it is removed (Salmoni et al., 1984; Winstein et al., 1994;
Anderson et al., 2005; Ranganathan and Newell, 2009).
Better outcomes were found if the decision for receiving feed-
back was controlled by the learner (Chiviacowsky and Wulf, 2002,
2005). Self-controlled feedback tends to be requested after
performances learners believed to be successful (Chiviacowsky and
Wulf, 2002, 2005, 2007). The reason why learners ask for EF after
good trials and why it is more effective than a rigid schedule of
feedback is unclear (Chiviacowsky and Wulf, 2002). However,
recent results point to motivation, where knowledge about
successful trials induces learners to reproduce the successful motor
pattern (Chiviacowsky and Wulf, 2002, 2007). These findings
indicate that providing feedback after good trials is superior than
after incorrect trials, nonetheless, it is uncertain whether it can be
applied to different motor tasks (Chiviacowsky and Wulf, 2007).
5. Feedback provision for the management of LBP
Different types of EF have been used during management of LBP
using various conceptual frameworks (Table 3). Positive results
from these studies are likely related to sensory-motor adaptation
occurring independently of type of EF. Even though, the selection of
optimal content and timing characteristics might influence motor
adaptation. The provision of EF in the management of LBP is dis-
cussed in light of previously described principles for the use of EF.
5.1. Content characteristics
5.1.1. Program and parameter feedback
One study (Magnusson et al., 2008) provided program feedback,
while all other studies focused on parameter feedback (Table 4).
The reason may be that therapists believe that LBP patients need to
improve specific features of movement patterns in order to
enhance the quality of such performed movements. Examples
reported in the literature, where parameter feedback was used,
include delayed contraction of transversus abdominis muscle
(Hodges, 1999), localized atrophy and reduced capacity to actively
recruit the lumbar multifidus muscle (Wallwork et al., 2009), as
well as, increased amount of spinal co-contraction (Flor and
Birbaumer, 1993; Newton-John et al., 1995; Marras et al., 2000)
increasing spinal loads (Marras et al., 2000). Nonetheless, it is
considered that motor program training and, consequently,
program feedback can enhance neural reorganization and motor
control (Shepherd, 2001; van Vliet and Heneghan, 2006). Since
motor control acquisition is task-specific, the isolated training of
a component of the movement might not be as useful as the
training of the functional task itself (Shepherd, 2001; van Vliet and
Heneghan, 2006; Shumway-Cook and Woollacott, 2007).
5.1.2. Amount of information during feedback provision
Two studies have provided summary EF (Herbert et al., 2008;
Magnusson et al., 2008). In addition, Herbert et al. (2008) results
support the provision of variable feedback schedule for improve-
ment of multifidus muscle recruitment. The literature supports the
provision of summary EF for motor learning, indicating that it has
a better influence on acquisition of a motor skill compared to EF
provided at the end of every trial (Schmidt et al., 1990; Guadagnoli
et al., 1996). However, other research suggests that there is an
optimal number of performance attempts prior to provision of
summary feedback (Schmidt et al., 1990). Theoretically, as the
complexity of the task is increased, the number of trials to be
included in the summary feedback is reduced (and consequently,
the frequency of feedback is increased) (Guadagnoli and Lee, 2004;
Schmidt and Wrisberg, 2008). Task difficulty will be related to
personal previous motor experience and the task itself (Guadagnoli
and Lee, 2004). However, for subjects with LBP, it is important to
consider the disruption magnitude of the intrinsic feedback system
(O’Sullivan et al., 2003; Brumagne et al., 2008b), since subjects with
increased proprioceptive disruption might benefit from more
frequent EF. Nonetheless, this has not been investigated in the LBP
population.
5.1.3. Performance bandwidth (error magnitude)
Two studies (Henry and Westervelt, 2005; Magnusson et al.,
2008) have used performance bandwidth during training of
abdominal hollowing maneuvers in healthy subjects (Henry and
Westervelt, 2005) and during rehabilitation program for LBP
(Magnusson et al., 2008). The former has used it for the control
group and the latter used it as a form of progression for reha-
bilitation spinal exercises. None of these studies have assessed
the effect of different bandwidth magnitudes on clinical
outcomes.
Table 4
Content characteristics.
Content Characteristics
Author (Year) Program Parameter Summary Average Bandwidth Focus of attention (Internal or External)
Vasseljen and Fladmark, 2010 No Yes No No No Not addressed
Magnusson et al. (2008) Yes Yes Yes No Yes External
Herbert et al. (2008) No Yes Yes (VAR group) No No Not addressed
Ferreira et al. (2007) No Yes No No No Not addressed
Worth et al. (2007) No Yes No No No Not addressed
Van et al. (2006) No Yes Yes No No Not clear (G1); External (for G2)
Teyhen et al. (2005) No Yes No No No Not addressed
Henry and Westervelt (2005) No Yes No No Yes (Control) Not addressed
Rasmussen-Barr et al. (2003) No Yes No No No Not addressed
Niemisto et al. (2003) No Yes No No No Not addressed
Hides et al. (1996) No Yes No No No Not addressed
Newton-John et al. (1995) No Yes No No No Not addressed
Donaldson et al. (1994) No Yes Not adressed Not adressed Not adressed Not adressed
Stuckey et al. (1986) No Yes No No No External
Bush et al. (1985) No Yes No No No Not addressed
Nouwen (1983) No Yes No No No Not addressed
Flor et al. (1983) No Yes No No No Not addressed
VAR ¼variable provision of EF group; CON ¼constant provision of EF group.
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5.1.4. Focus of attention
The use of external focus of attention on motor learning in
patients with LBP has not been compared to internal focus of
attention. Literature from the motor learning field suggests that EF
should be provided with an external focus of attention (Shea and
Wulf, 1999; Wulf et al., 2009). Similar results were found for
subjects with Parkinson disease (Wulf et al., 2009), who presented
a reduction on postural instability when instructed to perform
a task with an external focus of attention.
Magnusson et al. (2008) used an external focus of attention in
their trial of LBP treatment while Van et al. (2006) used external
focus of attention in healthy subjects during isometric contraction
of multifidus muscle. Their findings support the use of EF as an
additional tool for rehabilitation of LBP and training of multifidus
muscle contraction. However, other studies do not support better
learning or clinical outcomes from using EF (Henry and Westervelt,
2005; Teyhen et al., 2005; Worth et al., 2007; Herbert et al., 2008).
These four studies (Henry and Westervelt, 2005; Teyhen et al.,
2005; Worth et al., 2007; Herbert et al., 2008) provided visual
feedback to subjects and it is not clear what type of focus of
attention was provided. The different findings between those of
Van et al. (2006) and Worth et al. (2007) might be related, at least
partially, to the type of focus of attention used. While results by Van
et al. (2006) support the provision of EF (even during the retention
test, the EF group performed better), Worth et al. (2007) found the
feedback group performed better only during immediate assess-
ment. At the retention test, no difference was found between
groups (Table 6).
5.2. Timing characteristics
5.2.1. Concurrent and terminal feedback provision
Rehabilitative ultrasound imaging (visual EF) has been used to
enhance contraction of transversus abdominis (Worth et al., 2007).
However, Henry and Westervelt (2005) and Teyhen et al. (2005)
found provision of rehabilitative ultrasound imaging (visual EF)
did not enhance the ability to perform the abdominal drawing-in
maneuvre (Table 6). Although different explanations are presented
by the authors (Henry and Westervelt, 2005; Teyhen et al., 2005), it
is possible that the use of concurrent visual feedback influenced the
results. On the other hand, the findings from Van et al. (2006)
support the provision of concurrent feedback (Table 6). Due to
the conflicting evidence, it is clear more research is needed to
clarify this topic.
5.2.2. Frequency of feedback provision
Only one study tested how frequency of EF affected motor
learning in LBP (Herbert et al., 2008) and found reduced EF
frequency is better for motor learning purposes (Table 6). In the
present review, rehabilitative ultrasound imaging feedback was
considered as a form of parameter feedback (Table 2), aiming to
improve the control over specific muscles (generally multifidus or
transversus abdominis), instead of providing information about the
general movement pattern. Interestingly, the findings from Herbert
et al. (2008) are in contrast with other authors (Salmoni et al., 1984;
Winstein and Schmidt, 1990; Weeks and Kordus, 1998; Park et al.,
2000). Herbert et al. (2008) found reduction of EF frequency to be
useful for acquisition of parameters of fundamental pattern of
movement. Nonetheless, reduced frequency of EF appears to have
only a small influence on the parameters of the fundamental
Table 5
Timing characteristics
Author Concurrent Terminal Frequency
(Year) Immediate Delayed Constant Reduced frequency Self-controlled
Vasseljen and Fladmark, 2010 Yes Not clear Not clear Not clear No No
Magnusson et al. (2008) Yes Yes No Yes No No
Herbert et al. (2008) Yes (CON group) Yes (CON group) Yes (VAR group) Yes (CON group) Yes (VAR group) No
Ferreira et al. (2007) Yes No No Yes No No
Worth et al. (2007) No Yes No Yes No No
Van et al. (2006) Yes (G2) Yes (G1) No Yes No No
Teyhen et al. (2005) Yes No No Yes No No
Henry and Westervelt (2005) Yes (verbal & visual) Not clear Not clear Yes No No
Rasmussen-Barr et al. (2003) Yes No No Yes No No
Niemisto et al. (2003) Yes No No Yes No No
Hides et al. (1996) Yes Not clear Not clear Yes No No
Newton-John et al. (1995) Not addressed No No Not addressed Not addressed Not addressed
Donaldson et al. (1994) Yes Not addressed Not addressed Not addressed Not addressed Not addressed
Stuckey et al. (1986) Yes No No Yes No No
Bush et al. (1985) Yes No No Yes No No
Nouwen (1983) Yes No No Yes No No
Flor et al. (1983) Yes No No Yes No No
VAR ¼variable provision of EF group; CON ¼constant provision of EF group.
Table 6
Main findings for studies that compared the use or not of extrinsic feedback on
training or rehabilitation management.
Author (year) Main findings
Magnusson et al.
(2008)
Patients allocated in the feedback group presented
enhanced scores for VAS, SF-36 and kinematic measures.
Herbert et al. (2008) Variable feedback provision resulted in better multifidus
muscle recruitment, when compared to constant feedback
provision. During the retention test, the variable feedback
group also performed better.
Worth et al. (2007) The provision of ultrasound imaging improved short-term
performance for abdominal hollowing exercise,
nonetheless, retention test results demonstrated no
differences between the two groups.
Van et al. (2006) Participants that received ultrasound imaging feedback
improved motor recruitment for multifidus muscle and,
also, performed better during retention test.
Teyhen et al. (2005) Adding feedback did not improve contraction of
transverses abdominis muscle. One possible reason could
be insufficient training period.
Henry and
Westervelt
(2005)
The use of ultrasound imaging improved short-term
performance for lumbar stabilization exercise (specific
contraction for transverses abdominis). However,
retention test results demonstrated no differences
between the three feedback groups.
VAS ¼visual analogue scale; SF-36 ¼short form (SF) e36 questionnaire.
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pattern of movement (e.g. movement time, amplitude, speed),
when motor learning related to manual tasks, such as striking keys
in a board, was analyzed (Lai and Shea, 1998, 1999; Schmidt, 2003).
Although this consideration is only based on the results of one
study related to LBP (Herbert et al., 2008), further questions
include: how does pain experience, in subjects with LBP, influence
motivations and patterns of neural processing, when compared to
healthy participants, when (re)learning a task?; and how does
adaptive reorganization of motor cortex (Tsao et al., 2008),
considered to be present in LBP subjects, influence motor learning?
Magnusson et al. (2008) provided constant EF during the
intervention period. Even though that is argued to have a detri-
mental effect on motor learning (Lai and Shea, 1999), their results
were favourable for the use of EF. It is important to highlight that
the authors provided EF with the following recommended char-
acteristics: program and parameter feedback, an external focus of
attention, and summary feedback. It is possible that these charac-
teristics have prevailed over the negative effect of providing
constant EF. Moreover, the authors have used three different types
of EF: visual, auditory and success rates reports, as well as, variable
bandwidth (with increase in bandwidth precision as treatment
progressed). Thus the use of bandwidth seems to be useful when
followed by some form of instructional feedback (Butler et al.,
1996).
Six studies (Flor et al., 1983; Nouwen, 1983; Bush et al., 1985;
Stuckey et al., 1986; Donaldson et al., 1994; Newton-John et al.,
1995) have used the painetensionepain cycle as the theoretical
framework to support the use of electromyographic feedback for
LBP (Table 3). Nonetheless, other recent conceptual pain models
have been proposed and, it is clear that pain experience has a more
complex interaction with motor control response (Hodges and
Moseley, 2003; Moseley, 2003; Arendt-Nielsen and Graven-
Nielsen, 2008). No studies were found that investigated the use
of electromyographic feedback to improve specific muscle
recruitment for individuals with LBP.
There are other types of feedback commonly used by manual
therapists that were not included in the present review. One
example is the use of adhesive medical tape (Selkowitz et al., 2007;
Greig et al., 2008) as a feedback tool for rehabilitation. If tape is
used with the aim of augmenting the intrinsic feedback, then, the
same principles described above could be considered.
5.2.3. Future research directions
We found no evidence for a number of areas related to LBP and
EF. Whether there are differences between knowledge of perfor-
mance or knowledge of results EF on LBP outcomes; as well as, how
parameter or program EF, different focus of attention, immediate or
delayed terminal feedback and self-controlled EF influence LBP
outcomes still need to be clarified.
Considering the significant and clinically relevant outcomes
presented by Magnusson et al. (2008), the use of postural feedback
requires further exploration. The way in which postural feedback
influences motor control in subjects with LBP needs to be identified.
Finally, it is possible that different LBP clinical presentations will
respond in different ways to the provision of EF in its various forms.
This is an area that has considerable scope for research where
clarification of optimal responses has important clinical promise.
Additionally, we suggest that future research could, also, investigate
the use of electromyographic feedback in LBP rehabilitation.
6. Implications for clinical practice
Physiotherapists should consider the strong influence that
feedback can have on motor learning as well as rehabilitation
outcomes. Since the literature related to LBP and EF still needs to
explore a number aspects related to optimal EF delivery, recom-
mendations are based on the available literature primarily related
to the motor learning field, which has focused mainly in healthy
subjects. Generally speaking, physiotherapists should provide EF
with the following content characteristics: program feedback,
summary results feedback, and external focus of attention. With
regards to timing characteristics, concurrent and constant feedback
should be avoided. Reduced frequency or self-selected feedback has
stronger support and should be provided.
Acknowledgments
Support was provided by the University of Otago (PhD Schol-
arship). The authors would like to thank Mr. Richard German
(Faculty Librarian) in assisting with the electronic search strategy
for this study.
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D.C. Ribeiro et al. / Manual Therapy xxx (2011) 1e99
Please cite this article in press as: Ribeiro DC, et al., Extrinsic feedback and management of low back pain: A critical review of the literature,
Manual Therapy (2011), doi:10.1016/j.math.2010.12.001