Wobbly Lunges and the Evidence for Unstable Loads

by Dr. Brent Brookbush DPT, PT, MS, CPT, HMS, IMT

Surprising Research Findings: Unstable Loads

Research does more than provide objective data and statistics. It often inspires new ideas or new modifications to conventional exercises and techniques. For example, did you know that unstable loads likely increase muscle activity more than unstable environments? That is weights suspended by bands, Earthquake bars, and surge pipes will likely result in larger increases in muscle activity than Airex pads, stability balls, and balance boards. We didn't know this either… until we performed a comprehensive systematic research review for the course "Stability Training ". We have to say, integrating these unstable loads has been a ton of fun, has added a whole new direction for many of our exercise progressions, and has led to a couple of new personal records (PRs) among our athletes and staff.

Research Summary (Annotated Bibliography Below):

Position Statement: Unstable loads (weight hanging from bands, flexible barbells, or surge pipes) are likely to result in a significant increase in core and stabilizing muscle activity, and stability may be challenged by progressing from a barbell, to a barbell with weight hanging from bands, hanging weight from lighter bands, or hanging weight from a flexible barbell (e.g. Earthquake Bar). However, unstable loads may require the use of lighter loads (decreasing prime mover activity), significantly increase sway during repetitions, and decrease force output, implying use during high-intensity max strength and max velocity training may not be appropriate.

Legs: Unstable loads (weight hanging from bands or surge pipes) during lower extremity exercise is likely to result in a significant increase in core and stabilizing muscle activity and an increase in sway, but may result in a decrease in force output that is not ideal for high-intensity max strength and max velocity training.
Chest and Shoulder Press: Performing a chest press with a flexible barbell (e.g. Earthquake bar) or load hanging from bands (weight plates or kettlebells) may result in a significant increase in bar sway and EMG activity of stabilizing muscles, and hanging weight from lighter bands may result in further increases. However, the slower rep speeds and lighter loads (decreasing prime mover activity), may be inappropriate for use during max strength and max velocity training.
Shoulder Press: The one study located investigating the shoulder press (Williams et al., 2018) demonstrates findings that are congruent with the results from previously mentioned research investigating leg and chest exercises; however, this study did add the additional findings that stability could be challenged by progressing from a barbell, to a barbell with hanging weight, to a flexible barbell (e.g. Earthquake bar) with hanging weight.
Rows: The limited research available implies that EMG activity of latissimus dorsi, scapular stabilizers, thoracic extensors, and hip extensors may be higher when comparing rows with a suspension trainer to rows with more stable loads.

Additional Exercise Ideas

A Favorite Progression: Wobble Lunges

Written Instructions:

Start with the client or patient assuming good standing form/posture:
- 2nd toe pointing forward and under the ASIS
- Ankles, knees, and hips in alignment
- Pelvis neutral (absence of anterior or posterior pelvic tilt)
- Torso, scapula, and head in neutral alignment
Have the client or patient take a step back, with the intent that the front leg (target leg) will bear the load.
- Note, before performing any progression of a reverse lunge, it is recommended a few reps of a static or dynamic lunge are performed to determine the step width/length that results in ideal alignment in the bottom position.
Cue the client or patient to maintain a parallel tibia and torso angle (e.g. the client or patient should have a forward lean similar to the lean performed during a squat).
Once the client or patient has achieved the bottom position, have them perform the drawing-in maneuver, squeeze the glute of the target leg, and attempt to thrust that hip forward to attain the original standing position.
Have the client or patient perform a “form/posture check” and make any necessary adjustments.
Repeat for the desired number of repetitions.

Regressions and Progressions

Load Progression: Increase load, increase unstable loads, or decrease the strength of the band holding the load (do not use bands so weak they may snap during training).
To Balance: This exercise can be performed with the non-target foot returning to the starting position between repetitions, or the non-target foot can be elevated with 90 degrees of hip and knee flexion, with the intent to stabilize at the top of each repetition (in this variation the non-target-foot only touches the starting position at the beginning and end of a set).
Static and Dynamic Progression: This exercise can be performed as a static lunge, a dynamic reverse lunge, a dynamic reverse lunge to balance , a walking lunge, a walking lunge to balance , a forward lunge, and a forward lunge to balance .
Multi-planar Progressions: Although set-up must be carefully tested to ensure weights cannot swing and strike the exerciser during repetitions; frontal plane and transverse plane wobble lunges are incredibly challenging and may have significant functional benefits for athletes.

Selected Research and Annotated Bibliography

Legs

The studies below imply that unstable loads (weights suspended from bands and waterfilled tubes) significantly increase the muscle activity of trunk rotators, trunk extensors, and ankle plantar flexors, but may not have a significant effect on the muscle activity of the rectus abdominis or quadriceps. The rectus abdominis is likely unaffected because it does not perform the joint actions (extension or rotation) that would resist backloaded weight, and the quadriceps are prime movers that may be maximally recruited in response to sufficient load (regardless of the stability required). Interestingly, the study by Ditroilo et al. (2018) demonstrated that unstable loads have a larger influence on muscle activity and changes in the center of pressure (deviations or sway), than eyes open or closed. And, the study by Lawrence et al. (2015) noted a decrease in ground reaction force with unstable loads, which may imply unstable loads are not appropriate for all phases of training (e.g. high-intensity max strength and max velocity training). In summary, the use of unstable loads (weight hanging from bands or surge pipes) during lower extremity exercise is likely to result in a significant increase in core and stabilizing muscle activity and an increase in sway, but may result in a decrease in force output that is not ideal for high-intensity max strength and max velocity training.

Lawrence et al. compared 15 resistance-trained males (age: 24.2 ± 3.4 years) during back squats for 1 set, 10 reps/set, 60% of 1-RM loads, with stable and unstable loads. The stable load was a conventionally loaded barbell, and the unstable load was a barbell with weight plates suspended from bands. The finding demonstrated that the unstable load resulted in a small but significant decrease in ground reaction force (average 3.9% decrease), and a significant increase in EMG activity of the rectus abdominis, external obliques, and soleus. Note, stable and unstable loads resulted in similar EMG activity of the vastus lateralis, vastus medialis, biceps femoris, and erector spinae.
- Lawrence, M. A. and Carlson, L. A. (2015) Effects of an unstable load on force and muscle activation during a parallel back squat. Journal of Strength and Conditioning, 29(10), 2949-2953
Ditroilo et al. compared 18 male elite Gailic footballers (age: 21.7 ± 1.5 years) during an isometric squat with a water-filled training tube (half filled with water and a mass of 12.5kg) or conventional barbell (12.5 kg load), with eyes open, or eyes closed. Each condition was administered in random order during a single set of isometric squats for 15 seconds at a depth of 90-degree knee flexion, with 1 min rest between conditions. The findings demonstrated that the water-filled tube significantly increased the velocity and range of change in the center of pressure (larger changes in balance), and the EMG activity of the external obliques and multifidus, but not the rectus abdominis. Interestingly, eyes open and eye closed had an insignificant effect on the center of pressure and muscle activity for the conventional barbell squat, and decreased the range of change in the center of pressure for the water-filled tube condition.
- Ditroilo, M., O'Sullivan, R., Harnan, B., Crossey, A., Gillmor, B., Dardis, W. and Grainger, A. (2018) Water-filled training tubes increase core muscle activation and somatosensory control of balance during squat. Journal of Sports Sciences, 36(17), 2002-2008

Chest

These studies imply that adding unstable loads (flexible barbells or weights hanging from bands) to a chest press results in changes in the path of motion, rep speed, and alteration in muscle activity. Unstable loads are likely to increase the activity of stabilizing muscles, including the middle deltoid, supraspinatus, subscapularis, biceps brachii, and trapezius. However, the amount of load will have a larger influence on the activity of prime movers, including the pectoralis major, anterior deltoids, latissimus dorsi, and triceps muscles. Further, Lawrence et al. (2018) demonstrated that hanging weights from lighter bands is likely to make loads more unstable, and significantly increase the challenge of the exercise (note, be careful not to use bands that are so light that may fail during training). Additionally, Lawrence et al. and Ostrowski et al. (2017) demonstrated that unstable loads resulted in larger excursions in the path of motion (sway), a reduction in repetition speed, and a reduction in the load that could be lifted which may reduce prime mover EMG activity. Similar to the studies on leg exercise, this could imply that unstable loads are not appropriate for all phases of training (e.g. high-intensity max strength and max velocity training). In summary, performing a chest press with a flexible barbell (e.g. Earthquake bar) or load hanging from bands (weight plates or kettlebells) may result in a significant increase in bar sway and EMG activity of stabilizing muscles, and hanging weight from lighter bands may result in further increases. However, the slower rep speeds and lighter loads (decreasing prime mover activity), may be inappropriate for use during max strength and max velocity training.

Publications by Lawrence et al. and Ostrowski et al. (same experiment) compared 15 resistance-trained males (age: 24.2 ± 2.7 years, lifting experience: 9.9 ± 3.4 years, 1-RM bench press: 107.5 ± 25.9 kg) during a conventional barbell bench press (stable condition) and a flexible Earthquake bar bench press with weights suspended by bands (unstable condition). The participants performed unstable and stable conditions in random order, 2 sets/condition (measurements taken during the 2nd set), 5 reps/set, 75% of 1-RM load for the stable condition, 60% of 1-RM loads for the unstable condition, 2 minutes rest between sets, with a tempo "as fast as could be controlled." EMG activity was measured for the pectoralis major, anterior deltoid, middle deltoid, posterior deltoid, biceps brachii, triceps brachii, upper trapezius, and latissimus dorsi, as well as speed of repetitions and path of motion. The findings demonstrated that rep speed during the heavier stable condition was faster than the lighter unstable condition, and the lighter unstable condition resulted in larger deviations from a linear path of motion. Further, during the lighter unstable condition, participants exhibited more EMG activity from the middle deltoid and biceps brachii, and less EMG activity from the pectoralis major, anterior deltoid, and triceps brachii.
- Lawrence, M. A., Leib, D. J., Ostrowski, S. J. and Carlson, L. A. (2017) Nonlinear analysis of an unstable bench press bar path and muscle activation. Journal of Strength and Conditioning, 31(5), 1206-1211
- Ostrowski, S. J., Carlson, L. A. and Lawrence, M. A. (2017) Effect of an unstable load on primary and stabilizing muscles during the bench press. The Journal of Strength and Conditioning Research, 31(2), 430-434
Lawrence et al. compared 12 male powerlifters (age 28.6 ± 5.2 years, lifting experience: 9.8 ± 6.0 years, 5-RM bench press 133.6 ± 30.9 kg) during a conventional bench press 3 unstable conditions with a flexible barbell and suspended weights: plates handing from heavy (#1) mini bands, plates hanging from lighter (#3) bands, kettlebells hanging from heavy (#1) bands. The participants performed stable and unstable conditions in random order, 1 set/condition, 5 reps/set, 100% of 5-RM load for the stable condition, 2 minutes rest between sets, with a tempo "as fast as could be controlled." The analysis included superficial EMG activity of the biceps brachii, triceps brachii, deltoids, upper/middle/lower trapezius, pectoralis major, latissimus dorsi, serratus anterior, and infraspinatus, and fine-wire EMG activity of the supraspinatus and subscapularis. The findings demonstrate that EMG activity was highest during the conventional bench press for the anterior deltoid and pectoralis major, the EMG activity was highest during the conventional and heavy band conditions for the triceps brachii, and EMG activity was highest for the biceps brachii during the unstable conditions. Trapezius, supraspinatus, and subscapularis activity increased with increases in instability (conventional to heavy bands to lighter bands), and the middle deltoids exhibited the highest activity during the heavy band conditions.
- Lawrence, M. A., Ostrowski, S. J., Leib, D. J. and Carlson, L. A. (2018) Effect of unstable loads on stabilizing muscles and bar motion during the bench press. Journal of Strength and Conditioning Research.
Dunnick et al compared 20 resistance-trained males (age: 24.1 ± 2 years) during conventional bench press, barbell bench press with 16 kg kettlebells suspended from bands, and during light (60% of 1-RM loads), and heavy (80% of 1-RM load) conditions. Participants performed the light conditions or heavy conditions on 2 separate testing days in random order, each testing day included a stable and unstable condition, each condition was performed for 3 reps, with a moderate 2 sec/rep tempo and a pause at the bottom to prevent "bouncing", and presumably a long 3 min (or longer) rest between conditions. The findings demonstrated that EMG activity of the pectoralis major, anterior deltoid, meddle deltoid, triceps brachii, and latissimus dorsi was higher during the heavy condition; however, EMG activity for all tested muscles was similar during stable and unstable conditions.
- Dunnick, D. D., Brown, L. E., Coburn, J. W., Lynn, S. K. and Barillas, S. R. (2015) Bench press upper-body muscle activation between stable and unstable loads. The Journal of Strength and Conditioning Research, 29(12), 3279-3283

Shoulder Press

Similar to the research on leg and chest press exercises, performing a shoulder with a flexible barbell (e.g. Earthquake bar) or bands suspended from weights is likely to significantly increase sway and the EMG activity of some stabilizing muscles (latissimus dorsi and erector spinae). Unfortunately, this study likely did not use sufficient load to reach statistically significant differences in muscle activity for most of the muscles tested; however, the study did demonstrate that rate of perceived excursion and sway increased when progressing from a barbell, to a barbell with hanging weight, to a flexible barbell (e.g. Earthquake bar) with hanging weight.

Williams et al. compared 12 men (age: 25.3 ± 2.7 years, lifting experience: 7.3 ± 2.4 years, 1-RM standing overhead press 77.1 ± 11.5 kg) performing an overhead press with a conventional barbell, a barbell with kettlebells suspended from bands, and an Earthquake (EU) bar with kettlebells suspended from bands. The participants performed the conditions in random order for 10 reps/set, 50% of 1-RM loads, moderate (2:0:1) tempo, and long (5 min) rest between conditions. The assessment included the center of pressure excursion, rate of perceived exertion (RPE), fine wire EMG activity of the supraspinatus, infraspinatus, and subscapularis, and surface EMG of the latissimus dorsi, upper trapezius, serratus anterior, erector spinae, rhomboids, rectus abdominus, external obliques, pectoralis major, anterior/middle/posterior deltoid, triceps brachii, and biceps brachii. The findings demonstrated that RPE, and center of pressure excursion increased significantly from barbell, to barbell with suspended weight, to Earthquake bar with suspended weight. However, EMG activity was only significantly increased for the latissimus dorsi and erector spinae when comparing stable versus unstable conditions (all other muscles failed to exhibit significantly different activity for the 3 conditions). The barbell with suspended weight and earthquake bar with suspended weight resulted in similar EMG activity.
- Williams Jr., M. R., Hendricks, D. S., Dannen, M. J., Arnold, A. M. and Lawrence M. A. (2018) Activity of shoulder stabilizers and prime movers during an unstable overhead press. Journal of Strength and Conditioning Research, doi: 10.1519/JSC.0000000000002660

Rows

Unfortunately, the research investigating unstable loads during rows lacks the direct comparisons that may be necessary to develop nuanced conclusions. The available research implies that EMG activity of latissimus dorsi, scapular stabilizers, thoracic extensors, and hip extensors may be higher when comparing rows with a suspension trainer to rows with more stable loads.

Fenwick et al. compared 7 healthy men (age: 27.1 ± 3.8 years) while performing a bent-over row, a single-arm standing row, and an inverted row from a suspension trainer. The EMG activity was recorded during the second repetition of each exercise for the rectus abominis, external obliques, internal obliques, latissimus dorsi, erector spine (longissimus thoracis and iliocostalis), gluteus medius, gluteus maximus, rectus femoris and biceps femoris. The findings demonstrated that the inverted row resulted in the highest EMG activity for the thoracic erectors, latissimus dorsi, and hip extensors (gluteus maximus, gluteus medius, and biceps femoris), as well as the lowest recruitment of the lumbar erectors and he most neutral spine position.
- Fenwick, C. M., Brown, S. H., & McGill, S. M. (2009). Comparison of different rowing exercises: trunk muscle activation and lumbar spine motion, load, and stiffness. The Journal of Strength & Conditioning Research, 23(5), 1408-1417.
McGill et al. compared 14 males with resistance training experience (age: 21.1 ± 2 years) while performing rows, pull-ups, and chin-ups, from stable and unstable apparatus. The modeling used during the study implied that rows with a suspension trainer, when compared to inverted rows from a stable apparatus, had a significant influence on muscle recruitment.
- McGill, S., Cannon, J. and Andersen, J. (2014) Muscle activity and spine load during pulling exercises: influence of stable and labile contact surfaces and technique coaching. Journal of Electromyography and Kinesiology, doi: 10.1016/j.jelekin.2014.06.002
Snarr et al. compared 15 participants (11 males, age: 26.6 ± 4.2 years; 4 females, age: 22.3 ± 1.0 years) during inverted rows with a barbell and a suspension trainer. All participants performed 4 reps of each condition in randomized order with a long (3min) rest between conditions. The findings demonstrated that EMG activity for the two conditions was similar for the latissimus dorsi, posterior deltoid, and trapezius; however, biceps brachii EMG activity was higher during the barbell inverted row.
- Snarr, R. L. and Esco, M. R. (2013) Comparison of electromyographic activity when performing an inverted row with and without a suspension device. Journal of Exercise Physiology Online, 16(6), 51-58

A Note on the Available Research:

We wish there were more studies published investigating unstable loads; however, this is a relatively new idea in the exercise science and physical rehabilitation field. These studies do not compare unstable loads to unstable surfaces, so a definitive conclusion cannot be made about which is a larger stimulus. However, when comparing the research during our research review in the course Stability Training , there seems to be a trend that the addition of unstable loads consistently results in an increase in EMG of stabilizing and core muscles; whereas, the addition of unstable environments does not. Further, there also seems to be a trend in the research demonstrating that unstable environments result in a larger decrease in force output than unstable loads. This is not to imply that unstable loads are good and unstable environments are bad. In fact, we think every professional should incorporate both into their integrated performance enhancement and rehabilitation routines to gain all of the benefits that may be achieved from stability training. However, we are suggesting that if you have not tried unstable loads, you really need to! They could just be a little trick to help you achieve new levels of performance. For a much more thorough review of stability research, check out our course Stability Training.

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Questions, comments, and criticisms are welcome and encouraged

Wobbly Lunges and the Evidence for Unstable Loads