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Legs/Triple Extension
Progressions:
By Brent Brookbush, DPT, PT, COMT, MS, PES,
CES, CSCS, ACSM H/FS
Introduction
For a comprehensive review of unstable load and
surface training:
Stability Training
Relative Flexibility Progression:
Relative flexibility progressions are general
guidelines for exercise selection that can be used
while correcting postural dysfunction/movement
impairment. Individuals exhibiting signs of
lumbopelvic hip complex dysfunction (LPHCD) or
lower extremity dysfunction (LED) may reduce the
chance of compensation by integrating lower
body movement patterns in the following order:
1. Ball Wall Squats
2. Squats
3. Step-Ups
4. Lunges
Subsystems Recruited:
The majority of lower extremity exercises require
significant trunk stabilization and coordinated
recruitment of all core subsystems. The intrinsic
stabilization subsystem maintains segmental
stabilization and alignment, while balanced
recruitment of the anterior oblique subsystem
(AOS) and posterior oblique subsystems
(POS) prevent excessive flexion, extension, lateral
flexion and rotation of the lumbar spine. The deep
longitudingal subsystem (DLS) acts synergistically
with the POS to extend the hips and knees,
stabilize the sacroiliac joint and eccentrically
decelerate and/or isometrically stabilize the
lumbar spine.
Intrinsic Stabilization Subsystem (ISS)
Posterior Oblique Subsystem (POS)
Anterior Oblique Subsystem (AOS)
Deep Longitudinal Subsystem (DLS)
Kinesiology: Triple Extension
Hip Extension
Prime Mover: Gluteus maximus
Synergists: Biceps femoris (long head),
semitendinosus, semimembranosus and
posterior head of adductor magnus
Antagonists: Psoas, iliacus, tensor fascia
latae, rectus femoris, anterior adductors
(especially pectineus) and sartorius
Neutralizers: Gluteus minimus, anterior fibers
of gluteus medius, semitendinosus and
semimembranosus neutralize external rotation
force of gluteus maximus
Stabilizers: Deep rotators of hip
Fixators: Intrinsic stabilization subsystem
(ISS), anterior oblique subsystem
(AOS),posterior Oblique Subsystem
(POS) and deep longitudinal subsystem (DLS)
Knee Extension
Prime Mover: Quadriceps: vastus lateralis,
vastus medialis, vastus intermedius and rectus
femoris
Synergists: There are no true synergists of
knee extension. However, the gluteus maximus
and soleus can act as synergists during closed
chain movements by "pulling" the tibia and
femur posteriorly into knee extension.
Antagonists: Biceps femoris,
semimembranosus, semitendinosus, popliteus,
gastrocnemius, gracilis and sartorius.
Neutralizers: Careful balance between medial
and lateral stabilizers of the knee must be
maintained to prevent excessive internal or
external rotation of the tibia. More complex
relationships between synergistic pairs exist –
for example, the short head of the biceps
femoris and vastus medialis obliquus are
functional antagonists.
Stabilizers:
Medial stabilizers: Gracilis, semitendinosus
and semimembranosus, vastus medialis,
popliteus, medial gastrocnemius
Lateral Stabilizers: Gluteus maximus,
TFL, vastus lateralis via the iliotibial band,
biceps femoris, lateral gastrocnemius and
plantaris
Articularis genu
Fixators: Intrinsic stabilization subsystem
(ISS), anterior oblique subsystem
(AOS),posterior Oblique Subsystem
(POS) and deep longitudinal subsystem (DLS)
Ankle Plantar Flexion
Prime Mover: Soleus and gastrocnemius
Synergists: Fibularis longus, fibularis brevis,
tibialis posterior, flexor hallucis longus, flexor
digitorum longus, and plantaris
Antagonists: Tibialis anterior, extensor
digitorum longus, extensor hallucis longus and
fibularis tertius
Neutralizers: The tibialis posterior and medial
gastrocnemius neutralize the eversion force
created by the lateral gastrocnemius and
fibularis muscles.
Stabilizers: Fibularis longus, fibularis brevis,
tibialis posterior, tibialis anterior, flexor hallucis
longus, flexor digitorum longus, extensor
digitorum longus, extensor hallucis longus and
fibularis tertius
Fixators: Medial and lateral stabilizers of knee,
quadriceps, muscles of the foot.
Research Corner
Squats
Prime mover muscle activity during the barbell
squat may not be affected by unstable surfaces or
loads. Prime movers are defined as the
quadriceps and gluteal complex (gluteus
maximus and gluteus medius), and research has
investigated various unstable surfaces including
foam pads, Reebok Core® Boards, balance
boards, BOSU® balls and balance cones (15). Most research investigating vastus medialis
and vastus lateralis activity demonstrate that
training surface does not have a significant effect
on activity (2-5). However, a study using novice
exercisers found a significant increase in vastus
medialis and vastus lateralis muscle activity when
a foam pad was added to isometric squats (1).
This study could be compared to a study using
experienced exercises and a similar foam pad,
demonstrating no change in muscle activity (4).
This may imply novice exercisers exhibit an
increase in EMG activity to accommodate
unstable surfaces, however experience reduces
the need for this increase (1,4). Only one study
was found comparing the glute complex activity of
experienced lifters on stable and unstable
surfaces, and no significant difference in muscle
activity was noted (3). In summary, research
suggests unstable surfaces have little effect on
Prime mover muscle activity for experienced
lifters, but may increase muscle activity in novice
lifters. More research is needed to determine how
unstable surfaces contribute to the increases in
performance noted above; for example, increased
coordination, balance, reaction time.
Stabilizer muscle activity during a barbell squat
may be affected by unstable loads, but probably
not unstable surfaces. Research has investigated
lower-extremity stabilizers including the bicep
femoris, tibialis anterior,
gastrocnemius and soleus, as well as core
muscles including the rectus abdominis, external
obliques, erector spinae, and multifidus (2-7). A
study by Lawrence et al. demonstrated that
weight plates suspended from a barbell by bands
resulted in a significant increase in external
oblique, rectus abdominis and soleus muscle
activity (6), and Ditroilo et al. demonstrated that
squats using a water-filled tube significantly
increased external oblique and multifidus muscle
activity (7). The research studies mentioned above
also demonstrated that stabilizer and core muscle
activity were not significantly affected by unstable
surfaces (2-5). One study by Saeterbakken et al.
demonstrated an increase in soleus activity using
a BOSU® ball during a squat, but the increase in
activity did not reach clinical significance
(5). These studies suggest that unstable loads
have a much larger effect on Stabilizer and core
muscle activity then unstable surfaces, and if the
goal is an increase in muscle activity then unstable
loads may be preferred. Again, more research is
needed on unstable surface and balance training
to determine the factors contributing to the
increases in performance.
Summary
Adding unstable surfaces to a squat may
increase prime mover activity for inexperienced
lifters.
Adding unstable surfaces to a squat may not
alter EMG activity for stabilizers or prime
movers in experienced lifters.
Adding unstable loads to a squat significantly
increases stabilizer and core muscle activity for
experienced and inexperienced lifters.
More research is needed to determine how
unstable surfaces contribute to the increases in
performance noted above; for example,
increased coordination, balance, reaction time.
Comparing the Squat, Lunge and
Bulgarian Split-Squat
Muscle activity during squats has been compared
to the lunge and Bulgarian split-squat (4, 812). Stuart et al. compared Muscle activity during
squats and lunges using a 50 pound barbell;
demonstrating higher quadriceps and hamstring
Muscle activity during the lunge (8). However, a
study by DeForest et al. demonstrated that when
lunges were performed with half the weight used
for the squat, lunges exhibited similar Muscle
activity for the quadriceps and lower activity for
the biceps femoris (9). In studies comparing
squats to the Bulgarian split-squat, EMG activity
for the vastus medialis and vastus lateralis were
similar (9, 10), even when performed on an Airex
pad (unstable surface) (4). Squat, lunges, and
Bulgarian split-squats demonstrated similar
erector spinae activity, however, the Bulgarian
split-squat elicited higher external oblique, gluteus
medius and gluteus maximus activity (4, 9-12).
Biceps femoris activity was similar for the
Bulgarian split squat and squats when using
heavier external loading for the squat, but when
using loads of 3-10 repetition maximus (RM) for
each exercise, more biceps femoris activity was
exhibited during the Bulgarian split squat (4, 1012). One study by DeForest et al. (9) compared
Muscle activity during the Bulgarian split-squat
and lunges, with the Bulgarian split-squat
requiring similar quadricep Muscle activity and
higher hamstring Muscle activity. These studies
imply that careful attention to the load used during
the study is important for developing sound
conclusions. Prime mover activity is likely similar
during all exercises when loads are adjusted to
ensure failure in the same rep range. Hip and trunk
stabilizer Muscle activity is higher during
lunges and Bulgarian split-squats when compared
to squats. Bulgarian split squats exhibited the
most biceps femoris activity, and the lunge
exhibited the least, which may imply Bulgarian
split-squats should be avoided due to the
propensity of the biceps femoris to be over-active
in those individuals exhibiting signs of LowerExtremity Dysfunction (LED). In summary, the
reduction in biceps femoris activity and increase in
core and hip Muscle activity during lunges may
imply this is an ideal progression from squats.
Comparing the Squat, Step-up and
Single-leg Squat
Muscle activity during the squat has also been
compared to the step-up and single-leg squat (13,
14). These exercises are discussed separate from
the Bulgarian split-squat and lunge, because
the step-up and single-leg squat are truly
unilateral; performed on one limb without support
from the other. When no external load is added,
the step-up requires twice as much glute
complex activity as the squat, and the single-leg
squat requires significantly more glute
complex activity than the step-up (13). When a
barbell was used to add external load to the
squat and single-leg squat, the squat exhibited
similar gluteal complex and semitendinosus
activity, but higher quadricep, erector spinae and
bicep femoris Muscle activity (14). It is possible
that during these loaded studies the gluteal
complex reached a recruitment threshold, that
reduced the differences noted when larger loads
were used (13, 14). Interestingly, band resisted
abduction around the knee increased gluteal
complex muscle activity during the unweighted
squat, but decreased gluteal complex muscle
activity during the step-up and single-leg
squat (13). This is likely due to the step-up and
single-leg squat being open chain movements,
and the gluteal complex being unable to
contribute to abduction when the pelvis was not
fixed (by the other leg on the ground). That is, the
only means of resisting a valgus force at the knee
during an "open-chain" lower extremity exercise is
ankle eversion, because a planted foot on the
ground creates a stable base to "push" from. In
summary, an increase in gluteal complex muscle
activity may be achieved by progressing
from squats to step-ups to single-leg squats;
however, difference in EMG activity decrease
when external loads are used. Further, band
around the knees resisted abduction only
increases gluteal complex activity during close
chain activities.
Comparing the Unilateral Lower Body
Exercise on Stable and Unstable
Surfaces
EMG activity has been compared during various
unilateral lower-extremity exercises, on stable and
unstable surfaces (4, 15, 16). Krause et al.
demonstrated EMG activity during a body-weight
lunge was 9 - 22% maximal voluntary isometric
contraction (MVIC) for the rectus femoris,
hamstrings, gluteus medius, gluteus maximus and
adductor longus (15). Another study by Krause et
al. demonstrated EMG activity during a bodyweight single-leg squat was 50% MVIC for the
gluteus medius (16). These same studies
demonstrated that when an unstable surface was
introduced, %MVIC increased for the lunge, but
not for the single-leg squat (15, 16). A study by
Andersen et al. reported that %MVIC for a loaded
Bulgarian split squat was 140% MVIC for the
bicep femoris, rectus abdominis and external
oblique, and between 70-90% MVIC for the rectus
femoris, vastus medialis, vastus lateralis and
erector spinae (4). The much higher %MVIC in
these studies is likely due to the use of external
load; however, it is interesting to note that adding
an unstable environment to the loaded Bulgarian
split-squat actually reduced %MVIC of the erector
spinae and biceps femoris. The reduction in
activity when adding an unstable environment is
likely due to an inability to produce the same
amount of force, i.e. lift the same load, or lift the
same load at the same speed. In
summary, progression from a lunge to single leg
squat may increase glute complex activity, adding
an unstable surface to body-weight exercise is
likely to increase EMG activity; where as, adding
unstable surfaces to loaded exercise may reduce
the capacity to produce force. Consideration of
the phase of training and the client's goal may
dictate whether stability or load is the appropriate
progression. (Note, the Bulgarian split squat was
omitted for the reasons mentioned above).
Summary
The reduction in biceps femoris activity and
increase in core and hip muscle activity may
imply lunges are a better progression
from squats than Bulgarian split-squats.
Gluteal complex and core muscle activity
increases as you progress from squats to stepups to lunges to single-leg squats/deadlifts;
however, difference in EMG activity decrease
when external loads are added.
Adding an unstable environment to bodyweight exercise is likely to increase EMG
activity; where as, adding unstable
environments to loaded exercise may reduce
the capacity to produce force.
Band resisted abduction around the knees only
increases gluteal complex activity
during squats.
Note: Bulgarian split squats are not
recommended due to the increased
hamstring activity, stress on commonly
restricted hip flexors, and potential strain on
the knee.
Stability Progressions:
The leg/triple extension progressions discussed
below are built upon several "general
progressions" that can be applied to any exercise.
In this course these progressions were applied to
the movement pattern in conjunction with the
relative flexibility progressions, and then edited
based on feasibility and effectiveness.
Load
Surface
Type
Barbell
Dumbbell
Earthquake Bar
(band suspended
weights)
Position
Airex Pad
1.
Half-Foam Roll
2.
Uni-planer
Balance Board
3.
PB Disk
Bosu Flat Side
Up
Etc.
Held at sides
Back loaded
Front rack
Exercise Progressions:
Form Cues:
Posture:
Feet parallel (2nd toe pointing forward)
Feet, knees and hips in alignment
Pelvis neutral (no anterior pelvic tilt)
Tibia and torso at parallel angles from a
lateral view throughout movement.
Neural Spine (drawing-in maneuver or
bracing if necessary)
Neutral cervical spine (Chin-tucked & head
back, head should follow spine)
Key points:
It is often helpful to cue hips forward, or a "hip
thrust" on the concentric phase (instead of
"lifting up"). The "hip thrust" cue seems to
reduce erector spinae recruitment, reduce
excessive arching of the lumbar spine, and
increase glute activation.
There are an enormous amount of secondary
references on "ideal squat form". The squat
form recommended in these courses is based
on "an absence of any obvious movement
impairment". That is feet turn out, knees bow
in, knees bow out, excessive foward lean and
an anterior pelvic tilt may be correlated with
pain, dysfunction and/or increased risk of
future injury. For more information please see
our courses on the Overhead Squat
Assessment.
Bulgarian split squats are not recommended
due to an increase in biceps femoris activity,
compensation around commonly restricted hip
flexors, and potential strain on the knee of the
back leg.
Single-leg Touchdowns are discussed in
Deadlift Progressions
Squats Stability Progression:
1. Ball Wall Squat
2. Body Weight Squat
3. Body Weight Squat Unstable
4. Back Squat
5. Front Squat
6. Wobble Squat
Squat Form and Modifications:
04:03
Back Squat:
09:13
Front Squat:
07:20
Wobble Squat
07:22
Step-Up Stability Progressions:
Generally, unstable surfaces are not
recommended for step-ups, and great care should
be taken with back loaded resistance. Although
the height of a step-up may seem relatively low,
falling in the direction of the stance leg with or
with-out load can be hazardous.
1. Alternating Step-up
2. Single Leg Step-up
Sagittal
Frontal
Transverse
3. Step-Up to Balance
Sagittal
Frontal
Transverse
Step Ups:
03:01
Lunge Stability Progressions:
Note: How lunges are loaded can also be used as
a progression for every variation below:
1. Holding weight at sides
2. Front loaded
3. Unstable load (weights suspended from a
barbell with bands, or using liquid filled tubes)
1. Static lunge
Frontal plane
2. Static lunge unstable
Frontal plane
3. Dynamic lunge
Reverse
Sta
Pro
4.