A New Direction to Athletic Performance: Understanding the Acute and Longitudinal Responses to Backward Running

Abstract

Backward running (BR) is a form of locomotion that occurs in short bursts during many overground field and court sports. It has also traditionally been used in clinical settings as a method to rehabilitate lower body injuries. Comparisons between BR and forward running (FR) have led to the discovery that both may be generated by the same neural circuitry. Comparisons of the acute responses to FR reveal that BR is characterised by a smaller ratio of braking to propulsive forces, increased step frequency, decreased step length, increased muscle activity and reliance on isometric and concentric muscle actions. These biomechanical differences have been critical in informing recent scientific explorations which have discovered that BR can be used as a method for reducing injury and improving a variety of physical attributes deemed advantageous to sports performance. This includes improved lower body strength and power, decreased injury prevalence and improvements in change of direction performance following BR training. The current findings from research help improve our understanding of BR biomechanics and provide evidence which supports BR as a useful method to improve athlete performance. However, further acute and longitudinal research is needed to better understand the utility of BR in athletic performance programs.

Full text

REVIEW ARTICLE
A New Direction to Athletic Performance: Understanding
the Acute and Longitudinal Responses to Backward Running
Aaron Uthoff
1
•Jon Oliver
1,2
•John Cronin
1,3
•Craig Harrison
1
•Paul Winwood
1,4
ÓSpringer International Publishing AG, part of Springer Nature 2018
Abstract Backward running (BR) is a form of locomotion
that occurs in short bursts during many overground field and
court sports. It has also traditionally been used in clinical
settings as a method to rehabilitate lower body injuries.
Comparisons between BR and forward running (FR) have
led to the discovery that both may be generated by the same
neural circuitry. Comparisons of the acute responses to FR
reveal that BR is characterised by a smaller ratio of braking to
propulsive forces, increased step frequency, decreased step
length, increased muscle activity and reliance on isometric
and concentric muscle actions. These biomechanical dif-
ferences have been critical in informing recent scientific
explorations which have discovered that BR can be used as a
method for reducing injury and improving a variety of
physical attributes deemed advantageous to sports perfor-
mance. This includes improved lower body strength and
power, decreased injury prevalence and improvements in
change of direction performance following BR training. The
current findings from research help improve our under-
standing of BR biomechanics and provide evidence which
supports BR as a useful method to improve athlete
performance. However, further acute and longitudinal
research is needed to better understand the utility of BR in
athletic performance programs.
Key Points
The acute effects of backward running display
unique cardiorespiratory and biomechanical
responses compared to forward running. While
running backward appears to be demanding on the
cardiorespiratory system and require high total
activation of lower limb muscles it has been shown
to display less mechanical strain on the knee joint
when compared to forward running.
Research suggests that implementing backward
running into longitudinal athletic training programs
is associated with decreased injury prevalence,
increased lower limb strength and improved change
of direction performance.
Though the acute and longitudinal benefits of
backward running are many, it is currently under-
represented in the scientific literature when
compared to other forms of locomotion.
1 Introduction
It is understood that forward running (FR) is a propulsive
form of locomotion characteristic of most overground
sports. Running in humans is a method of terrestrial loco-
motion that can refer to a variety of speeds ranging from
jogging to sprinting. Running is unique to other forms of
&Aaron Uthoff
uthoffaaron@gmail.com
1
Sports Performance Research Institute New Zealand
(SPRINZ), AUT Millennium, AUT University, Auckland,
New Zealand
2
Youth Physical Development Unit, School of Sport, Cardiff
Metropolitan University, Cyncoed Campus, Cyncoed Road,
Cardiff CF23 6XD, UK
3
School of Health and Medical Science, Edith Cowan
University, Perth, WA, Australia
4
Department of Sport and Recreation, School of Applied
Science, Toi Ohomai Institute of Technology, Tauranga, New
Zealand
123
Sports Med
https://doi.org/10.1007/s40279-018-0877-5

terrestrial locomotion, i.e. walking or skipping, as it is
characterized by a single leg supporting the body for the
duration of foot–ground contact and periods of time when
both feet are in the air [1]. Superior FR speed is considered
an important component of success in most overground
sports [2–4]. Therefore, it is no surprise then that FR has
received much attention from both scientific and coaching
communities. Research on FR ranges from acute deter-
ministic biomechanical studies [5–10] to assessments of
longitudinal training studies [11–14]. Descriptive research
on acute variables that characterise superior forward dis-
tance running and sprint-running performances have helped
inform training methodology designed to improve running
velocity and running economy [15–18]. For example,
specific and non-specific training methods have been
developed to enhance force production, power output and
movement velocity, which are known biomechanical
determinants of FR performance in both youth and adult
populations [19–21]. However, while FR has received most
of the attention, other directions of locomotion, such as
backward running (BR), have been less well researched.
In the absence of any formal definition of BR in the
literature, BR in the context of this paper is defined as any
form of locomotion in a reverse direction where movement
is accomplished via a single leg of support throughout
foot–ground contact and both feet simultaneously in the air
between contralateral foot strikes. BR, like FR, occurs for
short periods of time during many overground sports [22].
A fundamental difference between BR and FR is the visual
perspective of the runner. During BR, an athlete must rely
on alternative sensory information due to a lack of visual
guidance experienced during FR [23,24]. BR and deriva-
tives, such as backpedaling, are basic movement patterns
utilized for agility actions in sports [25]. BR provides
athletes with a strategy to move in a desired direction and
maintain a view of the ball or opposition [26], while
reducing strain on the knee joint [27–29]. It has also been
recommended for use in sports training programs to
increase variability [30], prepare athletes for the demands
of competition [31,32], reduce injury rates [33–35] and
enhance performance [30,36–40].
Although BR may alter the normal visual orientation
relative to FR, it is a strategy used by athletes of all levels.
For example, elite soccer players spend approximately
3–4% of the match running backward [22]. This is inter-
esting when you consider that the same elite soccer players
only spend between 0.9 and 1.4% of the match sprinting
forward. In addition, top-class soccer players (ranked 1–10
on the official FIFA list) spend significantly more time
(p\0.05) running backward than moderately ranked soc-
cer players (ranked higher than 20 on the official FIFA list)
[22]. This suggests that BR can be employed as a useful
strategy among high performing soccer athletes.
Human locomotion is produced via central pattern
generators, i.e. an intraspinal network of neurons capable
of generating a rhythmic output [41]. It is generally
accepted that forward and backward walking are products
of the same central pattern generators [23], although some
contention exists about which pathways are responsible for
producing each direction of locomotion [23,42]. While
limited evidence exists for whether this phenomenon
extends to BR and FR [24], researchers have suggested that
training adaptations from BR may transfer to FR [23].
Although a shared neural circuitry might produce each
running direction, BR velocities are known to be slower
than FR velocities during maximal efforts [26,43]. In fact,
maximal velocities that can be achieved during BR are
approximately 70% of those that can be produced during
FR [26,43].
Although velocities achieved during BR are lower than
those observed during FR, BR is found in warm-up pro-
grams designed to reduce injury prevalence and improve
athletic performance [32–35,40]. The rationale for the
inclusion of BR in the warm-up has not been documented
to the knowledge of these authors; however, it may be due
to BR’s ability to demonstrate lower biomechanical strain
on the knee joint than FR [27–29,44], while also requiring
higher activation in the leg muscles [36] or simply to warm
up the muscles specific to the movement patterns encoun-
tered in the sport.
Currently, BR is a movement utilized as an injury pre-
vention method and injury rehabilitation technique
[45–48], yet little is known about the athletic benefits of
BR. Therefore, the purposes of this review are to (1)
explore and compare the acute responses of BR to FR; (2)
examine the effects of BR training on aspects of athletic
performance; (3) discuss the possible merits of BR as a
method to improve athletic performance; and (4) provide
future research recommendations into BR.
2 Search Strategy for Acute and Training Studies
From December 2016 to September 2017 a comprehensive
search of seven electronic databases (MEDLINE
[EBSCO], OVID, PubMed, ScienceDirect, SPORTDiscus,
Web of Science and Google Scholar) was performed. The
same databases were searched in January 2018 to identify
more recent articles of relevance. The following keywords
were used: ‘backward’, ‘retro’ ‘running’, ‘backpedal’.
2.1 Selection Method and Criteria
Results were limited to human studies, academic journals,
reviews and dissertations. The bibliographies of all
reviewed articles were hand searched and forward citation
A. Uthoff et al.
123

was used where applicable. All studies conducted on BR
that were published in the English language were included.
The study selection process involved removing duplicates,
screening for relevance on title and then abstract, and
finally screening the full-text articles using the inclusion/
exclusion criteria.
3 Acute Responses to Backward Running
versus Forward Running
An acute response can refer to a range of biomechanical or
physiological effects either during or immediately follow-
ing a stimulus. To realise the potential long-term training
effects of an exercise, it is important to understand the
immediate overt and underlying outcomes associated with
that movement. Running research has typically aimed to
identify the influence of speed [49–52] and resistance
[21,53] on acute responses, while generally overlooking
the effect of running direction on these deterministic
variables. Herein, acute energetic and biomechanical
comparisons are drawn between FR and BR. Figure 1
provides a visual comparison between BR and FR over the
stance phase of the gait cycle.
3.1 Energetics and Cardiopulmonary Responses
The energetic cost of running overground is determined by
the volume of active muscle necessary to propel an athlete
in their desired direction [54], the ability of muscle tendon
units to store and utilize mechanical energy [55], and the
rate at which force can be applied during foot–ground
contact [54,56]. It is important to consider these factors
when comparing how much energy is required during FR
compared to BR.
It has been reported that BR places greater metabolic
demands on the body than FR at relative and absolute
velocities [54,57,58]. Variables assessing energetic and
cardiopulmonary responses include indirect calorimetry
[59], oxygen consumption, heart rate and blood lactate
concentrates [54,57,58]. Measurements of indirect
calorimetry revealed that BR elicits 28% higher metabolic
cost compared to FR at 2.24 ms
–1
[59]. Oxygen con-
sumption, heart rate and blood lactate have also been
reported to be significantly higher during BR than FR at
2.68 ms
-1
[57,58]. This suggests that BR elicits a greater
energetic demand and cardiopulmonary response than FR
at a given speed.
Wright and Weyand [54] concluded that greater ener-
getic demands exhibited during BR were a result of a 14%
increase in average muscle force per unit of ground force
exerted during BR versus FR. This resulted in 10% more
muscle volume being activated to produce each unit of
ground force during BR compared to FR. These findings
are reported at relatively slow running speeds between 1.75
and 3.5 ms
–1
. Currently it is unknown whether compar-
isons of BR and FR at running speeds greater than 3.5 ms
–1
will result in similar reports of greater muscle volume
being activated during BR.
Another suggestion for why BR requires greater ener-
getic demands is that it is less reliant on the stretch–
shortening cycle [60,61]. Cavagna et al. [60] concluded
that BR relies less on eccentric work and more on con-
centric work because the muscle–tendon units are stretched
more slowly during the braking phase at the beginning of
foot–ground contact and shorten more rapidly during the
push at the end of foot–ground contact compared to FR at
similar absolute velocities. Accordingly, BR appears to be
more reliant on the contractile components of the motor
unit, which are known to require greater energy
Early contact Mid stance Toe-off
Backward running
Early contact Mid stance Toe-off
Forward running
Running direction
Fig. 1 Stance phase of
backward and forward running
Backward Running: A New Perspective to Athletic Performance
123

expenditure [62,63]. Therefore, BR is characterised by
greater metabolic energy expenditure when muscles are
exerting greater forces during concentric contractions and
lower forces during eccentric contractions.
The time available for developing force is important for
determining the energetic cost of a movement [64]. A
simple inverse relationship exists between the rate of
energy used for running and the time a foot applies force to
the ground during each stride [55]. Wright and Weyand
[54] concluded that the application of ground force during
both BR and FR explains the energetic cost regardless of
direction. Furthermore, they concluded that the rate at
which force can be applied during foot–ground contact is
higher during BR than FR [54]. This finding has relevance
to sporting applications because we know that rate of force
development seems to be primarily determined by the
capacity of motor units to produce maximal activation in
the early phase of explosive contractions (first 50–75 ms)
[65].
3.2 Kinematics
Running kinematics are biomechanical variables which
describe motion of the body (e.g. angles, velocities and
positions), without reference to the underlying forces that
cause the motion [66]. Detailing kinematics during running
is useful as the information provides overt visual and
quantifiable descriptions of movement. Typical kinematic
measures of running include joint kinematics (e.g. location
and orientation of body segments) and step kinematics (i.e.
contact time, flight time, stride length and stride fre-
quency). Empirical research pertaining to kinematic char-
acteristics of FR and sprinting, and the influence of training
on these variables, is plentiful (for review, readers are
referred to the articles of: Mero et al. [10,67], Novacheck
[68]). Unfortunately, relatively little information is avail-
able on the kinematics of BR.
3.2.1 Joint Kinematic
It appears that BR displays distinct differences (see Fig. 2)
in the displacement of the lower limbs compared to FR
[26,29,69]. Differences can be attributable to the reversal
of movement direction and the location and magnitude of
joint displacements over a stride cycle [29,69].
3.2.1.1 Ankle Range of Motion From the time a runner
leaves the ground until mid-way through the flight phase of
their stride, ankle kinematics display similar ranges of
motion (ROM) for both FR and BR [69]. However, dif-
ferences appear moments before ground contact of the foot,
characterised by a dorsiflexed position during FR and a
second plantarflexion phase during BR [69]. Mean ankle
range of motion over a stride cycle has been reported to be
52°–55°and 42°–47°during FR and BR, respectively
[26,69]. One possible explanation could be that the ankle
is anatomically designed to produce forward propulsion
[70]. The foot is therefore functionally constrained in BR
due to the angle of the ankle increasing, as opposed to
decreasing before foot–ground contact in FR, limiting the
overall ROM and propulsive potential of the joint [26].
3.2.1.2 Knee Range of Motion Knee ROM over the gait
cycle has been reported to be greater during both the flight
phase and stance phase of FR compared to BR at similar
absolute and relative running speeds [29,69,71]. BR is
characterized by greater knee flexion during initial foot–
ground contact and greater knee extension during late foot–
ground contact compared to FR [69]. Between early and
late foot–ground contact the knee undergoes less flexion
during BR than is experienced during FR [69]. These
findings indicate that the knee is less compliant during BR
compared to FR at similar absolute intensities. A discovery
from Cavagna et al. [61] that BR displays greater vertical
leg stiffness compared to running at similar speeds forward
supports this suggestion. Although it is unknown whether
these characteristics are true when comparing BR and FR
at similar relative intensities, several potential training
adaptations could result from decreased knee ROM and
increased vertical leg stiffness exhibited during BR. For
example, increases in vertical leg stiffness may translate to
greater utilization of the stretch–shortening cycle [72] and
reduce deformation of the lower extremities during FR and
high velocity movements such as sprint-running and
change of direction tasks [52]. However, this posit has yet
to be empirically tested.
3.2.1.3 Hip Range of Motion Mean ROM between 27°–
42°and 40°–69°have been observed at the hip for BR and
FR, respectively [26,69]. Increasing running velocity
results in concomitant increases in hip joint displacement
for both FR and BR [26]. Maximal hip flexion is rarely
achieved during either FR or BR, yet maximal hip exten-
sion is only seen during FR [69]. The lower ROM dis-
played during BR versus FR might be a result of anterior
musculotendinous structures of the hip, knee and abdomen
preventing overstretching during the flight phase of the
stride cycle [73]. This postulate seems logical, yet is cur-
rently untested.
3.2.2 Step Kinematic
Joint kinematics are known to be related to step kinematics
during running [74]. For instance, as running velocity
increases joint ranges of motion become greater, which
leads to concomitant changes in step kinematics, i.e. longer
A. Uthoff et al.
123

stride length [50,75]. Step characteristics are variables that
have been used by coaches and sports scientists to assess
running performance for decades [18,68]. For example,
optimal stride length has been recommended for submax-
imal and maximal phases of FR [6,76,77] and increases in
stride frequency are thought to determine maximal sprint
running performance [78,79]. To gain insights into the
relationship between running direction and step kinematics
researchers have analysed running performances at veloc-
ities ranging from 1.85–6.42 ms
-1
to 2.64–9.10 ms
-1
for
BR and FR, respectively [26,36,38,59,69].
Running velocity is considered a result of the interaction
between stride length and stride frequency [18], with
greater speeds achieved through large ground reaction
forces produced during short ground contact times [43]. It
has been reported that the distance between each ipsilateral
foot–ground contact, i.e. stride length, is significantly less
during BR than FR [54], where matched absolute speeds
have been reported to be 12% less [58,69] and relative
speeds 37% shorter [26,43]. Alternatively, stride fre-
quency has been determined to be significantly higher for
BR than for FR [54], with matched absolute speeds being
12% faster [58,69] and relative speeds showing 11%
higher turnover [26,43,80]. In BR, contact times have
been found to be 19% longer at self-selected speeds [29],
9% shorter at matched absolute speeds [38] and 5% greater
at relative speeds [43] compared to FR. Flight times, i.e.
time that neither foot is in contact with the ground, have
been shown to be lower for BR than FR by 9 and 25%
when compared at matched absolute and relative running
speeds, respectively [38,43]. These findings indicate that
BR is characterized by increased contact times and
decreased flight times which manifest as shorter stride
lengths and higher stride frequencies across a range of
speeds. Stride length and flight times appear to be influ-
enced to a greater percentage when matched at relative
running speed. This may be due to greater FR velocities
being achieved, as we have seen that BR is on average 30%
slower than FR [26,43]. FR appears to display advanta-
geous step kinematics for producing higher running speeds
than BR, although it is difficult to decipher the underlying
determinants due to limited published studies in this area.
3.3 Function and Activation of Leg Muscles During
Forward and Backward Running
As running speed increases, the need for greater forces to
produce longer stride length and higher stride frequency
appears to be controlled by increases in leg muscle activity
[81]. The activation of leg muscles during human loco-
motion is the result of learned programming patterns gen-
erated via the central nervous system [82]. The same
neurological system stimulated by afferent muscle, joint
and associated tissues is believed to produce both back-
ward and forward locomotion [23,83–85] and has been
suggested to extend to BR and FR [24]. This revelation has
led to researchers investigating how the function and
activation of musculotendinous structures of the lower
limbs change with running direction [36,38].
3.3.1 Muscle Function
The mechanical function of leg muscles is considered to
have developed in humans to propel us forward [86,87].
Fig. 2 Joint kinematics of backward running in relation to forward running [26,29,69]. The differences shown are relative to forward running.
ROM range of motion, BR backward running, FR forward running
Backward Running: A New Perspective to Athletic Performance
123

The quadriceps and tibialis anterior primarily serve to
attenuate eccentric braking force during early foot–ground
contact while the plantar flexors, hamstrings and gluteal
muscles assist in forward propulsion [49]. The functional
roles of lower limb muscles are interchanged between BR
and FR, whereby the anterior muscles of the legs become
the primary source of propulsion and posterior muscles
absorb braking forces during BR [69]. The findings of
Flynn and Soutas-Little [36] support this notion with their
discovery that the muscle firing patterns are unique to
running direction. Specifically, BR velocity is achieved by
large productions of activity during the shortening action of
the quadriceps and posterior lower leg muscles. The
pragmatic utility of this knowledge provides a method for
reducing eccentric strain on desired musculotendinous
structures of the leg, while potentially developing greater
concentric contractile adaptations.
3.3.2 Muscle Activation
If faster running velocities are related to increased muscle
activity [81], FR could be expected to be characterised by
greater activity than BR. However, the reality is that most
lower limb muscles display greater total activation over an
entire stride cycle during BR compared to FR [36,80]. The
greatest differences are present in the leg extensor/hip
flexor muscles with a range between 53.3 and 189.6%
greater activity over the stride cycle reported during BR
compared to FR at the same absolute speed [80]. These
findings are important because they are the driving force
for some clinicians and researchers claiming that BR can
be used to increase leg strength and power [38,88] and
restore muscle balance [36]. In addition to greater muscle
activation, the average muscle force per unit ground force
has been shown to be substantially higher (14%) for BR
than FR [54]. The researchers suggested that this was a
result of larger muscle forces at the ankle presenting during
BR, which may manifest due to the average active muscle
length being 4% shorter during BR than FR. This sugges-
tion seems plausible as muscles of the lower leg have
reported higher activation when length is decreased [89].
Practically, even at matched absolute speeds, this means
that the muscle spent 4% more time in a concentrically
contracted state over the stride cycle when the subject ran
backward.
3.4 Kinetics
Kinetic variables (i.e. vertical and horizontal forces) have
been shown to be important measures to determine running
performance [10,50,77,90]. The ability to generate large
forces in short periods of time characterizes fast running
speeds [43,90]. It is important to therefore quantify and
compare how forces are expressed during BR and FR to
understand the similarities and differences between run-
ning directions. Figure 3illustrates some key kinetics
associated with BR compared to FR.
3.4.1 Patellofemoral Joint Compressive Forces
BR has been suggested for clinical purposes because it has
been proposed to reduce the mechanical stress on the knee
compared to FR at matched absolute submaximal speeds
[27–29]. Using mathematical models, researchers have
calculated that the compression of the patella against the
femur, i.e. patellofemoral joint compressive force (PFJCF),
is on average 24% lower during BR than FR at relative and
absolute running speeds [27–29]. The general consensus is
that PFJCF is primarily influenced by knee extensor
moments, which have been reported to be, on average, 72%
higher in FR than BR [27–29]. Knee moments are influ-
enced by both the magnitude and location of the ground
reaction force relative to the foot [28]. Therefore, it is
necessary to understand how and where forces are
expressed during FR and BR to conceptualize the clinical
and performance implications of each running direction.
3.4.2 Magnitude and Location of Ground Reaction Forces
Whilst PFJCF is expressed to a lower degree in BR, the
magnitude and orientation of the ground reaction force
have been reported to be similar during both BR and FR
[28,38]. These magnitudes at relatively low running
speeds have been reported to be between 1.6 and 2.5 times
body weight for BR and 2.5 and 2.7 times body weight for
FR, respectively [38,91]. Weyand et al. [43] found that
peak vertical ground reaction forces during BR and FR
were 2.1 and 3.6 times body weight at maximal running
speeds, respectively. The FR ground reaction forces found
by Weyand and colleagues [43] are in agreement with other
researchers who have determined that a sprinter exerts
forces in excess of 3–4 times their body weight during FR
[10,92]. Weyand et al. [43] explained that a possible
reasoning for their finding was that running speeds at
which the forces were obtained were 6.42 and 9.10 ms
-1
for BR and FR, respectively. In addition to the magnitude
of force, knowing the location of force relative to the foot
is useful for determining how the forces will act upon the
body.
Although ground reaction force is distributed across the
entire body, the foot is the only point of contact with the
ground during running where forces are both attenuated
and generated via the musculoskeletal system [93]. The
location of ground reaction force has been identified to be
further forward on the foot at initial ground contact in BR
versus FR [28]. With the functional role of the knee and
A. Uthoff et al.
123

ankle muscles switching between BR and FR, the impli-
cations are that ground reaction forces may be attenuated
more by the ankle and foot complex, resulting in a
decreased moment arm between the ground reaction force
vector and the knee joint in BR. This knowledge adds to
our understanding of the magnitude and location of the
peak force experienced during running, yet provides little
information outside of a snapshot in time. Including
information about how forces are expressed before and
after peak ground reaction force is experienced may
enhance our understanding of how FR and BR are
generated.
3.4.3 Braking and Propulsive Forces
Kinetic variables such as breaking and propulsive force
expression and the rate at which force can be developed
may serve strength and speed coaches with useful infor-
mation when performance enhancement is the objective.
Ground reaction forces during running change from being
negative during early foot–ground contact (i.e. braking) to
being positive during late foot–ground contact (i.e.
propulsion) [60,66]. Measuring the duration and magni-
tude of braking and propulsive forces provides insights into
the demands of muscle components [94,95].
Running at a constant speed, the momentum lost during
braking must equal the momentum gained during propul-
sion [96]. The time the body undergoes braking forces has
been shown to be shorter in BR compared to FR at constant
speeds [60]. Alternatively, the time generating propulsive
forces has been found to be longer during BR than FR [60].
The differences in time during braking and propulsion
between BR and FR indicate that the mean force experi-
enced while braking is greater in FR, while the mean force
necessary for propulsion is greater during BR [61].
Expanding on the expression of force between BR and
FR, Cavagna et al. [60,61] discovered that the propulsive
power during BR is, on average, greater than the braking
power. Ultimately, the difference between BR and FR is
due to a significant increase of the average propulsive
power with a non-significant change in average braking
power. This information suggests that compared to FR, BR
may be less efficient at transferring eccentric energy to
concentric energy via the stretch shortening cycle [60,61],
therefore indicating that FR is more reliant on the elastic
components of the motor unit, while BR relies more
heavily on the contractile component. If increasing con-
tractile potential of lower limb motor-units is an objective,
then BR may be a method to enhance these qualities.
Fig. 3 Kinetics of backward running compared to forward running [27–29,38,43,60,91]. The differences shown are relative to forward
running. GRF ground reaction force
Backward Running: A New Perspective to Athletic Performance
123

3.4.4 Rate of Force Development
The speed in which the contractile elements of the muscle
can develop force, i.e. rate of force development [97], is an
important determinant of explosive potential across a range
of physical performance tasks differing in stretch–short-
ening cycle durations for both youth and adults [98–101].
Rate of force development during BR has been shown to be
approximately 22% greater than FR across speeds ranging
from 1.75 to 3.5 m s
-1
and was found to increase more
rapidly with speed in BR compared to FR, with the greatest
differences being realized at the highest speeds [54]. The
translation of these findings in a performance context is
that BR is less reliant on the parallel and series elastic
components of muscle, and appears to require greater
recruitment of the contractile components, particularly at
greater running speeds.
3.5 Summary
In summary, it seems BR provides a unique energetic and
biomechanics profile compared to FR (see Fig. 4). When
comparing the acute responses, BR shows less efficient
step kinematics and stretch–shortening cycle characteris-
tics for producing high running speeds when compared to
FR [26,29,43,60,61,69]. However, BR appears to dis-
play beneficial characteristics related to total muscle acti-
vation [36,80], average muscle force per unit ground force
[54], utilization of the contractile element of the motor unit
[60,61], lower knee joint loads [27–29] and higher rate of
force development [54] when compared to FR at matched
absolute and relative speeds. While this information is
promising for rehabilitation and performance purposes,
most research has been conducted at relatively slow speeds
where BR and FR were matched at absolute velocities.
Knowing that maximal BR speed is approximately 30%
slower than maximal FR speed [26,90], further research is
needed to conclude whether the available findings can be
translated to comparisons at higher, relatively matched
running speeds. Furthermore, as external resistance is
known to influence biomechanical determinants during FR
[21,53,102], the acute effects of adding resistance to BR is
unknown.
4 Longitudinal Responses to Backward Running
Training
4.1 Warm-up Programs to Reduce Injury
and Enhance Performance in Athletes
An integral purpose of most sports training programs is to
prevent injuries and enhance athletic performance. Thus,
warm-up protocols which include BR have been developed
and researched in adult and youth populations [35,103].
The most notable programs include the FIFA
11?[35,104], FIFA 11?Kids [34] performance
enhancement and injury prevention [48], HarmonKnee [45]
and Dynamic Warm-Up programs [105].
From a prevention perspective, these warm-up programs
have shown to statistically reduce lower limb overuse and
injury prevalence [106]. Additionally, it seems that these
programs can significantly enhance quadriceps and ham-
string strength [103,105], hamstring flexibility, [105],
sprint performance [31] and dynamic balance [107]. Whilst
the authors are aware that the warm-ups comprise of
multiple movements and it is difficult to disentangle the
contribution of each exercise to the researchers’ findings,
these results provide support for implementing warm-up
programs that includes BR.
4.2 Aerobic and Anaerobic Adaptations
of Backward Running
Two research teams have examined the longitudinal effects
of BR on physical and fitness adaptations [39,108], although
one must be cognizant that neither compared the effects to
FR. Terblanche et al. [39] tested the effects of a BR program
on physical and performance components of fitness in 26
habitually-trained females. After training BR three times a
week for 6 weeks, the training group decreased body fat by
2.4% (p=0.01), increased predicted maximal oxygen
uptake (VO
2max
) by 5.2% (p=0.01), improved FR economy
by 30.3% (p=0.01) and decreased blood lactate concen-
tration after submaximal FR by -17.1% (p=0.01). The
control group, which were not exposed to a training stimulus,
did not show significant improvements in any of the tests.
These findings provide some evidence that chronic BR can
improve both physical and performance components of
athletic fitness, however, whether it has any advantage over
FR remains unclear.
In a group of highly-trained male runners, Ordway and
colleagues [108] quantified the effects of a 5-week BR
training program on FR economy. The eight athletes
completed two training sessions a week for 5-weeks, which
resulted in significant improvements (2.54%; p=0.032) in
steady-state FR oxygen consumption, i.e. running econ-
omy. This finding is of importance because it is compa-
rable to improvements which have been reported after
strength, plyometric and altitude training interventions
[109–111]. Contrary to the findings of Terblanche et al.
[39], Ordway et al. [108] did not find significant changes in
VO
2max
or body composition following BR training. The
lack of improvement in VO
2max
might be a reflection of the
characteristics of the athletes, who were ranked above the
80th percentile in VO
2max
at the pre-test. Something to
A. Uthoff et al.
123

consider is that the post-test results were compared to the
post-familiarized results. While this is good scientific
practice, readers must be cognizant that the 5 weeks of
familiarization and 5 weeks of training followed the same
overload program, differentiated in run training intensity
by only 0.45 ms
-1
and fitness responses may have occur-
red during the first 5 weeks of familiarization. The above
findings support the hypothesis of previous researchers that
aerobic capacity could be improved from BR training due
to the relatively larger acute energetic costs and car-
diopulmonary demands BR places on the body compared
to FR [54,58,69]. One may argue that increasing the speed
of FR to impose higher aerobic and anaerobic demands
would be a more specific form of training; however, many
field and court sports are not unidirectional [112,113] and
athletes may benefit from the reduced knee joint loading
[27–29] and increased utilization of shortening muscle
actions [54] associated with BR. However, further research
is needed to validate such views.
4.3 Strength Adaptations of Backward Running
To the authors’ knowledge, only two research teams have
published research examining the changes in maximal
force production to BR training [38,114]. Swati et al. [114]
examined the effects of BR training on maximal voluntary
isometric contraction (MVIC) in a group of males between
18 and 25 years of age. Thirty participants were randomly
allocated to either a backward walking (2.48 ms
-1
),
backward running (3.48 ms
-1
) or a control group. The
subjects performed their respective exercise three times a
week for 6 weeks. It was found that the BR group signif-
icantly improved MVIC at 60°knee flexion by 10% in
relation to the control group. These increases in isometric
performance might be indicative of the isometric nature of
BR, i.e. heavy reliance on contractile element with smaller
range of motion [36]. It should be noted that this study did
not include a FR group, therefore direct comparisons
between the effectiveness of BR versus FR on strength
adaptations cannot be made from these findings.
Threlkeld et al. [38] compared the effects of an 8-week
BR versus FR training program on the isokinetic muscular
torque production (IMTP) in a group of ten adult runners
(six males, four females). The runners were assigned to
either an 8-week FR or BR training group. The FR group
was instructed to continue their normal FR program with
no changes, whereas the BR group gradually included BR
into their FR program. Subjects were encouraged to set a
Fig. 4 Key characteristics of backward running compared to forward running at relative and absolute speeds
[26–29,36,43,54,57–59,61,69,80]. The differences shown are relative to forward running. FR forward running
Backward Running: A New Perspective to Athletic Performance
123

10- to 12-min per mile pace (2.24–2.68 ms
-1
) during BR.
Improvements in knee extensor IMTP were over two times
greater in the BR group at 120°s
-1
and over fourfold
larger at 75°s
-1
compared to the FR group. Additionally,
the BR group showed significant improvements in ankle
plantarflexor IMTP at 120°s
-1
, which were nearly ten
times greater versus the changes in the FR group. The
changes indicate that BR could be a technique for
strengthening the quadriceps and plantarflexor muscles.
This study is beneficial as it is one of the few to include a
FR control group and provide direct insights into the utility
of BR training versus FR training.
4.4 Linear Speed and Change of Direction
Performance
Swati et al. [114] measured the effects of BR training on
change of direction speed in a group of males aged
18–25 years compared to a backward walking and control
group. The researchers found that BR and backward
walking training three times a week for 6 weeks signifi-
cantly improved change of direction performance by 3.86
and 2.38%, respectively, yet no significant changes were
found for the control group who were not exposed to any
training intervention (-0.66%). Change of direction per-
formance from pre- to post-testing was found to be sig-
nificantly different for the three aforementioned conditions,
with the greatest difference between the BR group and
control group (p=0.01). This research highlights the
ability of a 6-week BR training program to improve change
of direction performance in a group of male university aged
subjects. However, this study did not compare the training
effects of BR to FR.
One study compared the effects of BR training versus FR
training on linear sprint-running and change of direction
performance in seventeen highly-trained female athletes
[30]. The BR and FR groups followed the same training
programme biweekly for 6 weeks. The running was per-
formed at maximum intensity with work-to-rest ratios
between 1:5 and 1:3. Linear sprint-running performance did
not differ from pre-training to post-training for the BR group,
although the FR group showed declines in performance over
20 m, with significant (p\0.05) decreases of 6.46 and
4.54% over 5 and 10 m, respectively. Change of direction
performance for the BR group showed significant improve-
ments for all change of direction tasks, ranging from 2.99%
for the 505-agility test to 10.33% in a ladder test. The
improvements in the BR group were also found to be sig-
nificantly greater than the FR group, which showed a range of
improvements from 0.38% in the 505-agility test to 2.87% in
the ladder test. These findings suggest that BR training may
be used to improve change of direction performance and
maintain linear forward sprint-running performance.
4.5 Summary
The longitudinal adaptations to BR training appear to be
beneficial for improving aerobic and anaerobic perfor-
mance, isometric and concentric leg strength, and change
of direction performance. These adaptations offer valuable
insights into the possible applications of BR training in
sports training programs.
Studies that have quantified the effects of BR on phys-
ical and physiological adaptations are few and typically
carry a number of limitations, e.g. lack of FR versus BR
and/or lack of a training control group. From a practical
perspective, this means that coaches and athletes wishing to
use BR training do not have support for how to prescribe
intensity or load to systematically overload training for
their desired adaptations. It is unknown whether BR
training is the panacea for injury prevention or perfor-
mance enhancement. However, if BR is empirically
investigated using robust methodological approaches,
researchers and coaches may better understand the utility
of implementing BR into a sports training program.
5 Practical Application
Repetitive stress on musculoskeletal structures may lead to
overuse injuries. Therefore, BR may be a method to
increase training variability and reduce injury prevalence.
From a performance perspective, exercises such as the start
and acceleration phases during sprint running are known to
require large isometric and concentric muscular forces. It
may be hypothesised that BR could be used as a method to
train such movements based on the knowledge that BR
requires greater isometric and concentric demands of the
musculotendinous structures of the legs to propel the body
than constant speed FR at relative speeds. Furthermore,
reductions in total lower limb ROM expressed during BR
would allow the foot to be repositioned more rapidly and
increase stride frequency. Higher stride frequency dis-
played during BR might help improve the neurophysio-
logical functions of the body to increase maximal FR
performance. This is further supported by the fact that
greater vertical leg stiffness is associated with BR com-
pared to FR. High vertical leg stiffness is known to be
concomitant with greater maximal forward sprinting speed.
6 Conclusion and Research Suggestions
It appears that BR exhibits a unique energetic and biome-
chanical profile compared to FR. Whilst running speed may
be limited by musculoskeletal function during BR,
researchers have reported that the acute responses may be
A. Uthoff et al.
123

beneficial from both clinical and performance perspectives
compared to FR. Energetics and biomechanics encompass
a large portion of variables important for understanding the
demands of a movement, yet only a small number of sci-
entific investigations have researched these determinants in
BR.
Empirical support exists for implementing warm-up
programs that include BR into sports training programs to
both fortify athletes against injury and improve perfor-
mance. Additional evidence suggests that BR might be a
training strategy to improve cardiovascular and neuro-
physiological functions necessary for optimizing athletic
performance. Whilst empirically supported reports are
encouraging, longitudinal research on the training effects
of BR is scarce. Currently, the training studies conducted
on BR have been un-resisted, therefore it is unknown how
prolonged loading of BR may affect athletic performance.
Additionally, most of these training studies are not
designed to analyse the effects on trained athletes. Fur-
thermore, none have analysed the effects on paediatric
populations. Without knowledge in these areas, a dearth of
scientific insight exists pertaining to BR training.
The biomechanics of BR are relatively well understood
at slow running speeds, but little is known about how these
determinants change with relation to running velocity or
with various types of external resistance. Given this
information, it is suggested that more empirical research
should be conducted in this area. The findings of these
investigations may allow for a more complete under-
standing of how BR may be implemented into sports
training programs to achieve a desired training effect.
Until now, sports scientists have shown relatively little
interest in developing BR training strategies that could
improve athletic performance. The lack of research in this
area means that coaches must make decisions concerning
sport performance training without the support of empirical
data. It is our recommendation that future research inves-
tigate the influence of speed and resistance on the acute and
chronic effects of BR and FR. Additionally, we recom-
mend that explorations be conducted in both youth and
adult populations to understand whether BR is influenced
by either maturation or training history.
Compliance with Ethical Standards
Data Availability Statement The datasets generated during and/or
analysed during the current study are available from the corre-
sponding author on reasonable request.
Funding No sources of funding were used to assist in the preparation
of this article.
Conflicts of interest Aaron Uthoff, Jon Oliver, John Cronin, Craig
Harrison and Paul Winwood declare that they have no conflicts of
interest relevant to the content of this review.
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