Take Home Points
Studies have shown that there are decreases in force, power, and movement velocity when performing RT on unstable surfaces. Decreases in force with instability accompanied by a similar extent of muscle activation suggested that the dynamic motive forces of the muscles (the ability to apply external force) were transferred into greater stabilizing functions (Cug 2014). The decrease in force, power, and performance during instability may be caused by an increase in joint stiffness.
Cug (2014) examined training adaptations associated with a 10-week instability-training program. Participants were tested pre- and post-training for trunk extension and flexion strength and knee proprioception. Forty-three participants participated in either a 10-week (3 days per week) instability-training program using Swiss balls and body weight as resistance or a control group (n = 17). Swiss ball training was conducted 3 days (Mon-Wed-Fri) per week for 10 weeks. Each participant was given a ball that was sized in accordance to their height. The size of the ball was conducive to achieving >90° angle at both the hip and knee. The stability balls were either 55 or 65 cm in height. The volume of exercise was kept consistent for each individual. The exercise program progressed in difficulty by increasing the sets and repetitions (week 1: 2 sets of 6 repetitions to week 10: 3 sets of 14 repetitions) or duration (week 1: 2 sets of 30s to week 10: 2 sets of 60s). The exercise program progressed in difficulty by increasing the repetitions. Before each workout, participants warmed up with a 6-8 minute run at approximately 8 km/hr. Active dynamic stretching of the neck, shoulders, trunk, hips, quadriceps, hamstrings, abductor, and adductor muscles followed the run. Dynamic stretching has been reported to either facilitate or have no adverse effects upon subsequent performance (Behm and Chaouachi, 2011). Stretching exercises were also performed during the session and at the completion of each session. Rest intervals were approximately 30 seconds. Exercises were all performed on Swiss balls and included abdominal crunch, back extensions, supine hamstring curls, squats (Swiss balls supporting the back) to a position where thighs were parallel to the floor, and standing and kneeling on the Swiss balls. The trained group increased trunk extension peak torque/body weight (23.6%) and total work output (20.1%) from pre- to post-training while the control group decreased by 6.8% and 6.7% respectively. The exercise group increased their trunk flexion peak torque/body weight ratios by 18.1% while the control group decreased by 0.4%. Knee proprioception (combined right and left joint repositioning) improved 44.7% from pre- to post-training and persisted (21.5%) for 9 months post-training. In addition there was a side interaction with the position sense of the right knee at 9 months showing 32.1% less deviation from the reference angle than the right knee during pre-testing. An instability-training program using Swiss balls with body weight as resistance can provide prolonged improvements in joint proprioception and core strength in previously untrained individuals performing this novel training stress which would contribute to general health.
The idea of training specificity would suggest that increases in knee proprioception would be more beneficial with a training program that involved the same posture, velocity, and movement. Even though two of the six exercises in the training program included knee flexion and extension movements (squats and supine hamstring curl), they were not performed in a similar seated stable position as used in testing (Cug 2014). An instability training program using only Swiss balls was beneficial in improving knee proprioceptive sense. A decrease in joint proprioception may be a key component for recurring injuries.
The strengthening of trunk stabilizing muscles is an important consideration for activities of daily living such as bending, twisting or lifting (Cug 2014). Weak trunk muscles have been shown to be a factor for low back pain (LBP) problems. Studies have shown that people with a history of LBP had weaker trunk muscle strength when compared to those who had not experienced LBP. Training the core musculature improves the stabilizing system, providing protection against spinal injuries. This study demonstrates that instability training using body mass as a resistance can be an effective training tool to increase core strength in everyone. COR provides an individualized personal training and physical therapy of exercises that may be experiencing any low back pain how to properly instruct you to fire your muscles correctly, and progress your activity in a pain-free and safe manner.
1. Cuğ M, Ak E, Ozdemir RA, Korkusuz F, Behm DG. The effect of instability training on knee joint proprioception and core strength. J Sports Sci Med. 2012 Sep 1;11(3):468-74.
Written by Chris Barber, CPT