Research Bites Vol. 6
Welcome back for another installment of Research Bites! For all of you who missed my research posts on my Instagram (@science_of_falling), you came to the right place. Every few weeks I will be posting a new set of five quick and dirty research reviews with the main findings, how it was performed, and my quick take on it.
The trick is, I only have the space of an Instagram caption (2200 characters) to dive in and extract main points. It makes for a fun challenge! If you want to see these posts sooner, head on over to Instagram and hit that follow button.
Enjoy that tasty research!
A study by Silva et. al. published in 2018 set out to discover the effect wobble board (WB) training has on balance ability in a single leg stance (SLS).
Study Details
🔸20 active men; 9 in control group (CG), age 26 ± 3 years old; 11 in training group (TG), age 25 ± 2 years old
🔸Experimental testing consisted of data intake 24 hours before training (PRE), two intermediate session after every 4 training sessions (INT-1, INT2), and 24 hours after last training (POST) for both groups
🔸Experimental sessions included:
↪3 x 30s SLS on a force platform (firm surface [FS]); contralateral hip and knee flexed to 30 degrees
After 3 min rest, SLS on WB on top of force platform, goal to maintain board flat for 60s recording period
↪Participants also monitored with motion capture system using reflective markers on body, as well as EMG on major LE muscle groups
*testing performed barefoot
🔸Training:
↪TG underwent 12 training sessions over four weeks, 30 mins long, 3x/week
↪15 balance exercises using a WB
↪60s work/60s rest
Study Findings
🔹No significant changes in balance time for FS SLS after study
🔹WB balance times in the TG were significantly improved at follow-up testing nearly by 3x; no significant change in CG found beyond task familiarity
🔹TG showed decreased trunk counter-movement velocity and increased contra-lateral leg counter-movement velocities to counteract the WB oscillations
🔹TG board angular velocity decreased by 40-50% in both the frontal and sagittal planes
🔹TG showed decrease muscle activation after the 4 week training intervention, while CG's increased
My Take 🤓
Previous studies have shown the need for counter-rotation mechanisms when proprioceptive input is not sufficient as discussed in the article. Using the WB increases the ability to use these counter-rotation strategies while decreasing the need for heightened muscular acitivity. This may show improved overall motor control with a changing base of support on unstable surfaces such as wet grass or sand. This study also shows that strength training on these surfaces, as often reported, is not an efficient way to build strength due to decreased muscle activation.
A study published in 2018 by Siqueira et. al. set out to determine if the toe-touch test (TTT) is a reliable test of posterior chain flexibility and how much balance ability affects the outcomes.
Study Details
🔸20 healthy active young adults
↪6 men; 14 women
↪24.9 +/- 5.3 years old
🔸Underwent TTT with markers placed in 7 places along the body while two cameras captured their positioning
🔸Stood on a force plate with predetermined foot placement in order to capture a reading for center of pressure (CP) at baseline
↪30 second trial of quiet upright standing on force plate performed to establish baseline CP
🔸Participants then performed TTT in two different conditions in the following order:
(1) standard TTT (ST)
(2) minimised postural demand TTT (MPD) - using a strap around the front of the participants hips to prevent a forward fall eliminating the balance demand of the test
(3) Retest of ST (RST)
🔸After reaching final position, participants held position for 10s while data collected
Study Findings
🔹ST showed CP position near baseline, ankle angle wide at 108 deg, and TTT outcome was averaged to be 15.2 cm, no participant reached the ground
🔹MPD showed CP moved forward for all participants by mean 5.2 cm, increased flexion of ankle and trunk angles, TTT outcomes increased to an average of 4.1 cm (73% increase), 6 participants were able to reach the ground
🔹RST showed results in the middle of the two prior testing conditions for CP position, body angles, and TTT outcome measurement
My Take 🤔
It's always interesting to me to see how much balance can affect what we percieve to be other avenues of fitness. The classic TTT, or otherwise known as a standing hamstring stretch, seems to be highly influenced by our ability to maintain balance in this position. As the results show, taking the balance aspect out of the stretch increases "flexibility" immensely. But what is also interesting is that the RST also showed improvements over the initial ST condition. This may be due to the brain undergoing a brief stint of motor learning and adapting what it discovered in the MPD condition to non-supported TTT.
A study by Hak et. al. published in 2012 investigated whether gait speed is ⬇️ when gait stability is challenged during ambulation, and if this may ⬇️ the probability of falling.
Study Details
🔸9 healthy subjects: 4 men/5 women; ages 32.2 +/- 7.5 years
🔸subjects walked on Computer Assisted Rehabilitation Environment (CAREN)
↪treadmill mounted onto a 6-degree-of-freedom motion platform
↪motion platform was used to induce perturbations in mediolateral (ML) direction during walking
↪12 infra-red cameras and Lower Body Plug-in-Gait marker set were used to capture kinematic data
↪safety harness system suspended overhead prevented the subjects from falling but did not provide any weight support
🔸Protocol:
↪2 warm-up trials on treadmill for 3 minutes (self-paced)
↪Experimental portion consisted of 10 trials of 4 min walking
↪Walking conditions included unperturbed condition, balance perturbations at 4 different intensities in the ML direction
↪Each conditon repeated twice for a total of 10 trials with one trial variation at a self-paced speed, and one at a fixed speed
↪all trials given at random
Study Findings
🔹During self-paced trials subjects did not significantly reduce walking speed in response to balance perturbations
🔹During the fixed speed trials,walking speed was lower compared to the self-paced trial, no interaction withperturbation intensity was found
🔹Step parameters were significantly affected by the perturbations:
↪Step length ⬇️ with ⬆️ perturbation intensity
↪Step frequency ⬆️ with an ⬆️ in perturbation intensity
↪Step width was significantly ⬆️ at all the perturbation intensities
🔹Subjects ⬆️ their backward and sideward margins of stability (MoS) meaning a ⬇️ risk of falling
-MoS is quantified as the distance between the centre of mass (CoM) motion state relative to the base of support
My Take 🤓
This study makes sense if you think about it in terms of extremely slow walking. Just because we reduce our speed to a crawl does not mean more stability. Those with ⬆️ levels of balance problems naturally have ⬇️ strides, ⬆️ step rate, and a ⬆️ step width whether they walk fast or slow.
A study by Lattimer et. al. published in 2018 set out to discover the differnced of younger women (YW) and older women (OW) during a simulated forward fall.
Study Details
🔸19 YW (mean age 23.0 yo +/- 3.8 years) and 16 OW (mean age 68.2 yo +/- 5.3 years)
🔸Isometric, concentric, and eccentric strength of non-dominant upper limb taken with isokinetic dynamometer
↪Performed in plane of movement that mimiced muscle activation patterns of controlled forwards descent
🔸5 simulated forward fall trials
↪Performed on FOOSH (Fall on outstretched hand) replication apparatus (FRA) which was custom built for the study and contains two force platforms
↪FRA adjusted to a 30 deg body angle prior to fall and subject harnessed in for safety
↪Instructed to fall initially with outstretched arms shoulder width apart and shoulders at 90 degs flexion; palms hovering 1cm over force plates
↪Quick release drop activated after a 1-5 second delay to allow a real simulated fall
↪Subjects instructed to "have a soft landing by using elbow flexion"
🔸Upper extremity electromyography (EMG) used to measure muscle activity during falls
🔸Motion capture system used to see kinematics of the fall
🔸Elbow angle at impact (ImA), elbow angular velocity (ImV), and elbow angle at 200ms post-impact (EnA) extracted from data
Study Findings
🔹OW showed ⬇ concentric elbow extension strength compared to YW; isometric and eccentric strength not significantly different
🔹YW had significantly ⬆ ImA, ImV, and EnA compared to the OW
🔹YW had 36% ⬆ peak energy absorbtion (ENRG) at impact
🔹YW had ⬆ correlation of concentric strength and peak ENRG
🔹OW had ⬆ correlation of all strength types and ENRG
My Take 🤓
According to this study YW tend to have better force absorbtion during a forward fall perhaps due to their greater elbow angles upon landing in conjunction with control at these angles. OW showed a stiffer landing and lower elbow velocity leading to less ENRG. Perhaps training the pushup in elderly populations can improve this control and thus landing mechanics. Improved ENRG at impact may result in decreased incidence of FOOSH injury.
A study published by Ding et. al. in 2016 investigated the relationship between muscle weakness and slip-related falls among community-dwelling older adults.
Study Details
🔸36 healthy older adults
🔸R knee strength (flexor and extensor) measured with isokinetic dynamometry to determine peak torque
🔸10 minutes after muscle testing, participants underwent treadmill testing to determine preferred normal walking speed
🔸Afterwards, subject put on ActiveStep Treadmill for testing with intentional slip-inducing motions
↪Subjects harnessed in and told not to grab onto rails or harness when a slip occurs
↪moment of slip unknown to subjects
↪Underwent 5 initial non-slip walking trials for 15s
↪On a 6th trial, slip perturbation induced after 10-12 steps by speeding up the treadmills top belt by 8 m/s^2
↪14 slip trials induced total throughout the session
🔸Motion capture system used to look at full body kinematics
🔸Load cell on harness measured force of falls
↪Synchronized with motion capture data for analysis
↪Falls = peak load cell force exceeding 30%
Study Findings
🔹All subjects experienced balance loss after perturbation
↪17 (47.2%) fell and 19 (52.8%) recovered
🔹Knee strength capabilities significantly lower in fallers than non-fallers
🔹Knee extensor strength could predict slip outcome with sensitivity of 64.7%/specificity 68.4%
🔹Knee extensor strength could predict fall in 66.7% of subjects
🔹Knee flexor strength could predict fall in 61.1% of subjects
🔹A decrease in knee extensor strength by .36Nm/kg increased risk of falling by 3.23x
🔹A decrease in knee flexor strength by .29Nm/kg increased risk of falling by 2.30x
🔹Optimal cutoff value to determine fallers was found to be 1.05 and 1.10 Nm/kg for knee extensor and flexors, respectively
My Take 🤓
Strong legs get the job done and make you safer as you age! I consistently praise balance and strength work with my patients. It's quite common to see one of my 65+ patients doing a loaded squat variation, and sometimes even single leg squats. No matter your age, I advise adding in some functional strength training to keep everything strong and ready to go when life tries to take you down.
Thanks for reading the sixth volume of Research Bites! I hope you learned a tidbit or two. Be sure to follow my Instagram account to see these research bites right away, and comment below on what you think about the findings above.
Happy Falling!
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