Lower Limb Muscle Activation During the Sit-to-Stand Task in Subjects Who Have Had a Stroke

Effects of Limbs' Spasticity on Spinopelvic Alignment in Post-Stroke Patients: A Cross-Sectional Study

Objectives: This study aimed to determine the impacts of upper and lower limb (UL and LL) spasticity and impairment on spinal alignment in chronic post-stroke patients. Methods: A total of 45 consecutive chronic post-stroke patients, 18 women and 27 men, from 18 to 70 years old who presented post-stroke hemiparesis were recruited in this cross-sectional study. The clinical assessment included the Modified Ashworth Scale (UL-MAS and LL-MAS spasticity), Upper Limb Motricity Index (UL-MI), FAST-UL, and Five Times Sit-to-Stand Test (5T-STS); the Associated Reaction Rating Scale was used to measure associated reactions in the hemiparetic UL, the plumb line distance from the spinous process of C7 on the sagittal (PL-C7s) and frontal plane (Pl-C7f), the kyphosis apex (PL-AK), and the spinous process of L3 (PL-L3). Angular measures of spinal alignment were measured by a Bunnell scoliometer™ (angle of trunk rotation-ATR) and a gravity-dependent inclinometer (inclination at C7-T1 and T12-L1). Results: In chronic post-stroke patients, there was found to be an association between the 5T-STS and PL-C7f (β = 0.41, p = 0.05) and the angle of inclination at T12-L1 (β = 0.44, p = 0.01). The FAST-UL correlated with PL-C7f (β = -0.41, p = 0.05), while the UL-MI correlated with this last parameter (β = -0.36, p = 0.04) and the ATR (β = -0.31, p = 0.05). The UL-MAS showed correlation with the ATR (β = 0.38, p = 0.01). Conclusions: The results lead to the possibility that, in chronic post-stroke patients, spinal misalignment on the frontal and sagittal plane is associated both with strength impairment and UL spasticity. The improvement or restoration of spinopelvic parameters can take advantage of therapeutic interventions targeted at motor improvement and spasticity reduction of the hemiparetic side.

Effects of Visual-Motor Illusion via Image Videos Showing Increased Exercise Intensity on the Tibial Anterior during Sit-to-Stand Movement: A Study of Healthy Participants

Visual-motor illusion (VMI) elicits kinesthetic sensation from visual stimulation. We have previously performed ankle motion VMI with resistance applied to the ankle joint on the paralyzed side (power-VMI (P-VMI)) and ankle motion VMI without resistance (standard-VMI (S-VMI)) to activate the tibialis anterior (TA) muscle in stroke-paralyzed patients and compared sit-to-stand (STS) durations, but these studies did not measure TA activity during the STS movement. The purpose of this study was to evaluate the effects of different intensities of visual stimuli presented during VMI on TA and STS movement. Healthy right-footed adults (n = 18) observed two different VMI videos of ankle dorsiflexion, including S-VMI and P-VMI, with an observation time of 2 min each. STS movement was evaluated before and after watching each video. Each participant performed both S-VMI and P-VMI interventions on the same day. Only P-VMI enhanced the integrated electromyogram of the TA, increased the angular velocities of the trunk forward inclination and the ankle dorsiflexion, and shortened the STS duration. Our results indicate that P-VMI facilitates the activation of TA during STS, and we believe that we have clarified the intervention mechanism of VMI.

Rollator usage lets young individuals switch movement strategies in sit-to-stand and stand-to-sit tasks

The transitions between sitting and standing have a high physical and coordination demand, frequently causing falls in older individuals. Rollators, or four-wheeled walkers, are often prescribed to reduce lower-limb load and to improve balance but have been found a fall risk. This study investigated how rollator support affects sit-to-stand and stand-to-sit movements. Twenty young participants stood up and sat down under three handle support conditions (unassisted, light touch, and full support). As increasing task demands may affect coordination, a challenging floor condition (balance pads) was included. Full-body kinematics and ground reaction forces were recorded, reduced in dimensionality by principal component analyses, and clustered by k-means into movement strategies. Rollator support caused the participants to switch strategies, especially when their balance was challenged, but did not lead to support-specific strategies, i.e., clusters that only comprise light touch or full support trials. Three strategies for sit-to-stand were found: forward leaning, hybrid, and vertical rise; two in the challenging condition (exaggerated forward and forward leaning). For stand-to-sit, three strategies were found: backward lowering, hybrid, and vertical lowering; two in the challenging condition (exaggerated forward and forward leaning). Hence, young individuals adjust their strategy selection to different conditions. Future studies may apply this methodology to older individuals to recommend safe strategies and ultimately reduce falls.

Analysis of inter-joint coordination during the sit-to-stand and stand-to-sit tasks in stroke patients with hemiplegia

BACKGROUND

Inter-joint coordination is an important factor affecting postural stability, and its variability increases after fatigue. This study aimed to investigate the coordination pattern of lower limb joints during the sit-to-stand (Si-St) and stand-to-sit (St-Si) tasks in stroke patients and explore the influence of duration on inter-joint coordination.

METHODS

Thirteen stroke hemiplegia patients (five with left paretic and eight right paretic) and thirteen age-matched healthy subjects were recruited. The Si-St and St-Si tasks were performed while each subject's joint kinematics were recorded using a three-dimensional motion capture system. Sagittal joint angles of the bilateral hip, knee and ankle joints as well as the movement duration were extracted. The angle-angle diagrams for the hip-knee, hip-ankle and knee-ankle joint were plotted to assess the inter-joint coordination. The inter-joint coordination was quantified using geometric characteristics of the angle-angle diagrams, including perimeter, area and dimensionless ratio. The coefficient of variation (CV) was performed to compare variability of the coordination parameters.

RESULTS

There were no significant differences in the perimeter, area and dimensionless ratio values of the bilateral hip-knee, hip-ankle and knee-ankle inter-joints during Si-St and St-Si tasks in the stroke group. The perimeter values of bilateral hip-knee and knee-ankle inter-joints in the stroke group were lower (P<0.05) than in the healthy group during Si-St and St-Si tasks. Although no significant bilateral differences were found, the inter-joint coordination in stroke patients decreased with the increased movement duration of both Si-St and St-Si tasks. Additionally, the CV of the hip-knee inter-joint area during the Si-St task in the stroke group was less than (P<0.05) that in the healthy group.

CONCLUSION

Stroke patients exhibit different inter-joint coordination patterns than healthy controls during the Si-St and St-Si tasks. The duration affects joint coordination, and inter-joint coordination is limited on the hemiplegic side joint pairs, which may lead to inconsistency in the rhythm of the left and right leg inter-joint movements and increase the risk of falls. These findings provide new insights into motor control rehabilitation strategies and may help planning targeted interventions for stoke patients with hemiplegia.

Effects of visual-motor illusions with different visual stimuli on the sit-to-stand of people with hemiplegia following stroke: A randomized crossover controlled trial

BACKGROUND

The objective of this study was to determine the effects of different visual stimuli during visual-motor illusion on sit-to-stand in people with hemiplegia following stroke.

METHODS

This was a randomized crossover controlled trial. Twenty people with hemiplegia following stroke were randomly divided into groups. The video images used for visual-motor illusion were ankle dorsiflexion without resistance (standard visual-motor illusion [standard illusion]) and maximum effort dorsiflexion with resistance (power visual-motor illusion [power illusion]). People with hemiplegia following stroke underwent both illusion interventions with a 1-week washout period in between; group A started with the standard illusion intervention and group B started with the power illusion intervention. Outcomes included the sit-to-stand duration, maximum weight-bearing value, trunk movement during sit-to-stand, ankle joint movement during sit-to-stand, and active ankle dorsiflexion movement on the paralyzed side.

RESULTS

The angular velocity of the trunk and ankle joints increased significantly during sit-to-stand, and sit-to-stand duration decreased significantly in response only to power illusion. In addition, the change in angular velocity of active ankle dorsiflexion was significantly greater in response to power illusion than was the change in response to standard illusion.

CONCLUSION

Power illusion induces a greater improvement in paralyzed ankle dorsiflexion function than standard illusion, resulting in shorter sit-to-stand duration.

Trunk and lower extremity biomechanics during sit-to-stand after stroke: A systematic review

OBJECTIVES

This systematic review aimed to pool available evidence of differences in trunk and lower extremity biomechanics during the different phases of a sit-to-stand (STS) task between persons with stroke and to healthy controls.

METHODS

Four electronic databases (Medline, Web of Science, EMBASE, and Cochrane Library) were systematically searched up to, and including, December 2021. Studies were included if they investigated kinematic, kinetic and/or electromyographic outcome measures of adults with stroke during STS and compared results with healthy controls. Data from eligible studies were categorized according to STS subphases if reported (Phase I: Movement onset to seat-off; Seat-off; Phase II: Seat-off to movement termination; Whole task [if no subtasks reported]). The Newcastle-Ottawa Scale was used to assess risk of bias.

RESULTS

Twenty-one studies were included in this systematic review. Methodological quality ranged from 13% to 75%; mean score was 55%. The findings of this systematic review suggest that after stroke, people rise to stand (phase I) with increased lateral trunk flexion and displacement of the center of pressure (COP) towards the non-paretic side, decreased anterior pelvic tilt, decreased hip flexion and altered timing of lower limb muscle activation. In addition, during phase II, lateral pelvic translation and weight distribution asymmetry was increased, knee extension velocity was decreased and delayed, stabilization was decreased and COP velocity was increased compared with healthy subjects.

CONCLUSIONS

This systematic review clearly showed changes in kinematics, kinetics and muscle recruitment after stroke, with differences between the different phases of STS. Therapeutic interventions should focus on subphases of this functional task to optimize performance in daily living.

Gluteus Maximus Muscle Activation Characteristics During a Chair-Rise in Adults With Chronic Stroke

BACKGROUND AND PURPOSE

A successful chair-rise is an important indicator of functional independence post-stroke. Lower extremity electromyographic analyses provide a basis for muscle activation from which clinical intervention protocols may be derived. Gluteus maximus activation during the chair-rise has not been thoroughly researched in the chronic stroke population. This study investigated the magnitude and onset of gluteus maximus activation during the chair-rise comparing adults post-stroke with healthy controls.

METHODS

In this cross-sectional study, adults with chronic stroke (n = 12) and healthy controls (n = 12) completed 4 natural-speed chair-rise trials. Magnitude and onset of bilateral gluteus maximus activation were measured during the movement with secondary comparative data from biceps femoris and vastus lateralis muscles. Kinetic and kinematic measurements were used to quantify chair-rise phases and movement cycle duration.

RESULTS

Significant decreases in paretic ( P = 0.002), and nonparetic ( P = 0.001) gluteus maximus magnitudes were noted post-stroke compared with ipsilateral extremities of healthy adults. Significant gluteus maximus onset delays were noted in paretic extremities compared with nonparetic extremities post-stroke ( P = 0.009) that were not apparent in comparative muscles. Similar onset times were noted when comparing the paretic extremity post-stroke to the ipsilateral extremity of healthy controls ( P = 0.714) despite prolonged movement cycle durations in those with chronic stroke ( P = 0.001). No onset delays were evident in the biceps femoris ( P = 0.72) or vastus lateralis ( P = 0.338) muscles.

DISCUSSION AND CONCLUSIONS

Despite apparent unilateral muscle weakness post-stroke, bilateral decreases in gluteus maximus activation magnitudes and compounding onset deficits of the paretic extremity were observed during chair-rising. Further research is needed to determine whether interventions maximizing bilateral activation magnitudes and improving temporal activation congruency during chair-rising will carry over to functional gainsVideo Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A387 ).

Clarify Sit-to-Stand Muscle Synergy and Tension Changes in Subacute Stroke Rehabilitation by Musculoskeletal Modeling

Post-stroke patients exhibit distinct muscle activation electromyography (EMG) features in sit-to-stand (STS) due to motor deficiency. Muscle activation amplitude, related to muscle tension and muscle synergy activation levels, is one of the defining EMG features that reflects post-stroke motor functioning and motor impairment. Although some qualitative findings are available, it is not clear if and how muscle activation amplitude-related biomechanical attributes may quantitatively reflect during subacute stroke rehabilitation. To better enable a longitudinal investigation into a patient's muscle activation changes during rehabilitation or an inter-subject comparison, EMG normalization is usually applied. However, current normalization methods using maximum voluntary contraction (MVC) or within-task peak/mean EMG may not be feasible when MVC cannot be obtained from stroke survivors due to motor paralysis and the subject of comparison is EMG amplitude. Here, focusing on the paretic side, we first propose a novel, joint torque-based normalization method that incorporates musculoskeletal modeling, forward dynamics simulation, and mathematical optimization. Next, upon method validation, we apply it to quantify changes in muscle tension and muscle synergy activation levels in STS motor control units for patients in subacute stroke rehabilitation. The novel method was validated against MVC-normalized EMG data from eight healthy participants, and it retained muscle activation amplitude differences for inter- and intra-subject comparisons. The proposed joint torque-based method was also compared with the common static optimization based on squared muscle activation and showed higher simulation accuracy overall. Serial STS measurements were conducted with four post-stroke patients during their subacute rehabilitation stay (137 ± 22 days) in the hospital. Quantitative results of patients suggest that maximum muscle tension and activation level of muscle synergy temporal patterns may reflect the effectiveness of subacute stroke rehabilitation. A quality comparison between muscle synergies computed with the conventional within-task peak/mean EMG normalization and our proposed method showed that the conventional was prone to activation amplitude overestimation and underestimation. The contributed method and findings help recapitulate and understand the post-stroke motor recovery process, which may facilitate developing more effective rehabilitation strategies for future stroke survivors.

Effects of kinesthetic illusion induced by visual stimulation on the ankle joint for sit-to-stand in a hemiparesis stroke patient: ABA' single-case design

[Purpose] The purpose of this study was to investigate the effect of kinesthetic illusion induced by visual stimulation to the paralyzed side ankle joint on the sit-to-stand of a hemiparesis stroke patient. [Participant and Methods] A 33-year-old male with left hemiparesis due to a right putamen hemorrhage participated. This study used the ABA’ single-case design. Phase A and A’ conducted only conventional physiotherapy. Phase B conducted kinesthetic illusion induced by visual stimulation and conventional physiotherapy. To create a kinesthetic illusion, a video image of the patient’s ankle joint dorsiflexion movement on the non-paralyzed side was inverted and placed on the patient’s paralyzed ankle. The patient observed this display for 5 min. We evaluated weight-bearing symmetry values during sit-to-stand, duration of sit-to-stand, trunk and ankle joint movement on the paralyzed side during sit-to-stand, active ankle dorsiflexion angle on the paralyzed side, and the composite spasticity score. [Results] The weight-bearing symmetry values, movement of the ankle dorsiflexion during sit-to-stand, active ankle dorsiflexion angle, and composite spasticity score were significantly improved in phase B as compared with phase A and the effect was sustained in phase A’. [Conclusion] Kinesthetic illusion induced by visual stimulation for a hemiparesis stroke patient affected the ankle dorsiflexion function, resulting in an improved asymmetry during sit-to-stand as assessed by weight-bearing symmetry values.

Proprioceptive neuromuscular facilitation induces muscle irradiation to the lower limbs - A cross-sectional study with healthy individuals

INTRODUCTION

This study aimed to evaluate the effectiveness of proprioceptive neuromuscular facilitation (PNF) in promoting muscle irradiation to the lower limbs and to relate these findings with muscle activation during the sit-to-stand task.

METHODS

Twenty-four healthy women were recruited via convenience sampling and submitted to four PNF patterns: upper limb pattern with flexion-abduction-external rotation (UL), lower limb pattern with flexion-adduction-external rotation with knee flexion (lower limb pattern 1 [LL1]), lower limb pattern with flexion-abduction-internal rotation with knee flexion (lower limb pattern 2 [LL2]), and lifting to the right. Electromyography was recorded from the gluteus maximus, gluteus medius, vastus medialis, vastus lateralis, and soleus during the PNF patterns and during the sit-to-stand task.

RESULTS

The most recruited muscles during the sit-to-stand task were the vastus lateralis, vastus medialis, and soleus (p < 0.05). Lifting to the right induced the greatest activation of the gluteus maximus (p < 0.001). Lifting to the right and LL2 were better than UL at recruiting the gluteus medius (p < 0.05). Lifting to the right and LL1 were better than UL at recruiting the vastus medialis and lateralis (p < 0.05; p < 0.05). and Lower limb pattern 1 and 2 were better than UL at recruiting the soleus muscle (p < 0.05).

CONCLUSION

PNF can be used to induce muscle irradiation to maintain or improve muscle activity to the muscles recruited during the sit-to-stand task. The best PNF pattern for inducing muscle irradiation to muscles recruited during the sit-to-stand task are lifting to the right, LL2, and LL1.

Comparing cortico-motor hotspot identification methods in the lower extremities post-stroke: MEP amplitude vs. latency

Transcranial magnetic stimulation (TMS) is a technique used to probe and measure cortico-motor responses of the nervous system. However, lower extremity (LE) specific methodology has been slow to develop. In this retrospective analysis, we investigated what motor evoked potential metric, amplitude (MEP_amp) or latency (MEP_lat), best distinguished the motor-cortical target, i.e. hotspot, of the tibialis anterior and soleus post-stroke. Twenty-three participants with stroke were included in this investigation. Neuronavigation was used to map hotspots, derived via MEP_amp and MEP_lat, over a 3cm × 5cm grid. Distances between points with the greatest response within a session and between days were compared. Both criterion, amplitude and latency, provided poor identification of locations between trials within a session, and between multiple visits. Identified hotspots were similar only 15 % and 8% of the time between two assessments within the same session, for amplitude and latency respectively. However, MEP_amp was more consistent in identifying hotspots, evidenced by locations being less spatially distant from each other (Amplitude: 1.4 cm (SD 0.10) Latency: 1.7 (SD 1.04), P = 0.008) within a session and between days (Amplitude: 1.3 cm (SD 0.95), Latency 1.9 cm (SD 1.14), P = 0.004). While more work is needed to develop LE specific methodology for TMS, especially as it applies to investigating gait impairments, MEP_amp appears to be a more consistent criterion for hotspot identification when compared to MEP_lat. It is recommended that future works continue to use MEP_amp when identifying tibialis anterior and soleus hotspots using neuronavigation.

Changes in Muscle Activation and Ground Reaction Force of the Lower Limbs According to Foot Placement During Sit-to-Stand Training in Stroke Patients

OBJECTIVE

The aims of the study were to investigate the kinetic effects of sit-to-stand training in various foot positions on the coronal plane in patients with strokes and to suggest appropriate exercises.

DESIGN

Thirty-six poststroke subjects participated in this study. The subjects performed three sit-to-stand trials in the following foot positions: (a) symmetric foot positioning (symmetric), (b) affected foot placed to the side (asymmetric 1), and (c) and less affected foot placed to the side (asymmetric 2). They were asked to perform sit-to-stand training at a spontaneous velocity and remain standing for 5 secs, whereas the vertical ground reaction force was measured using force platforms. The activation of lower limb muscles was evaluated using surface electromyography, and the peak and mean vertical ground reaction force and weight-bearing symmetry ratio were evaluated using force platforms.

RESULTS

Our results showed significant increases in the muscle activation, peak and mean vertical ground reaction force, and weight-bearing symmetry ratio of the lower limbs using the asymmetric 2 strategy (P < 0.05).

CONCLUSIONS

Our results suggest that sit-to-stand training with the less affected foot placed to the side by the width of the subject's foot may be the most beneficial in the rehabilitation of patients with hemiparetic stroke.

Correlation between lower limb muscle asymmetry during the sit-to-stand task and spatiotemporal gait asymmetry in subjects with stroke

The purpose of this study was to investigate the relationship between the both lower limb muscle asymmetry during sit-to-stand (STS) and spatiotemporal gait asymmetry in subjects with stroke. Twenty-nine patients were included in this study, lower limb muscle (rectus femoris, tibialis anterior, gastrocnemius) asymmetry during STS, five times sit-to-stand (FTSTS) and spatiotemporal (speed, step length, step time, swing time, stance time, single support time) gait asymmetry were measured. According to the results of the measurement, significant positive correlations between gastrocnemius and rectus femoris asymmetry during STS and step length asymmetry. Furthermore, significant positive correlations between rectus femoris asymmetry during STS and step time asymmetry. In addition, significant negative correlations between the FTSTS and gait speed. This study's results suggested that necessary to apply exercise that the gastrocnemius and rectus femoris symmetry during STS for improving step length and step time symmetry of gait, and necessary to apply exercise that increase STS speed for gait speed.

Neuromechanical Differences Between Successful and Failed Sit-to-Stand Movements and Response to Rehabilitation Early After Stroke

BACKGROUND

Recovery of the sit-to-stand (StS) movement early after stroke could be improved by targeting physical therapy at the underlying movement deficits in those people likely to respond.

AIM

To compare the movement characteristics of successful and failed StS movements in people early after stroke and identify which characteristics change in people recovering their ability to perform this movement independently following rehabilitation.

METHODS

Muscle activity and kinematic (including center of mass, CoM) data were recorded from 91 participants (mean 35 days after stroke) performing the StS movement before (baseline), immediately after (outcome), and 3 months after (follow-up) rehabilitation. Three subgroups (never-able [n = 19], always-able [n = 51], and able-after-baseline [n = 21]) were compared at baseline with the able-after-baseline subgroup compared before and after rehabilitation.

RESULTS

The subgroups differed at baseline for quadriceps onset time ( P = .009) and forward body position when quadriceps peaked ( P = .038). Following rehabilitation, the able-after-baseline subgroup increased their forward position ( P < .001), decreased the time difference between bilateral quadriceps peaks ( P < .001) and between quadriceps and hamstrings peaks on the nonhemiplegic side ( P = .007). An improved performance in the always-able subgroup was associated with a number of baseline factors, including forward positioning ( P = .002) and time difference between peak activity of bilateral quadriceps ( P = .001).

CONCLUSIONS

This neuromechanical study of StS before and after rehabilitation in a sample of people early after stroke identified the importance of temporal coupling between forward trunk movement and quadriceps and hamstrings' activity. These findings advance the science of stroke rehabilitation by providing evidence-based therapy targets to promote recovery of the StS movement.

Evaluation of the Keeogo™ Dermoskeleton

Purpose: (1) To determine the specific functional characteristics of individuals with neurological impairments that may predict successful use of Keeogo™ dermoskeleton and (2) to quantify the specific benefit Keeogo™ provides to a regular user of the device. Methods: Thirteen individuals (seven males; six females; 52 ± 4.6 years old) with mobility impairments due to neurological disease or injury were recruited. Berg Balance Sale (BBS) score and Timed Up and Go (TUG) performance were used to identify baseline characteristics in participants. The 6-min walk test (6MWT) and 25-foot walk test (25FWT) were performed with the participants wearing and not wearing the dermoskeleton; a successful user of Keeogo™ displayed a ≥ 5% improvement in walking performance while wearing the device. A chronic stroke survivor (hemiparesis on left side) completed the stair climb test (SCT) and the 30-second chair stand test (30CST) with and without Keeogo™. Muscle activity, kinetics and postural control were analyzed during the sit-to-stand (sitTS), and compared to an age- and sex-matched healthy control. Results: Successful users of Keeogo™ have a moderate level of functionality (BBS: 46-51 s and/or TUG: 8-12 s). Wearing Keeogo™ improved performance on the 30CST, SCT and improved motor control, postural control and movement kinetics during the sitTS task in a chronic stroke survivor with significant hemiparesis. Conclusion: This is the first study providing data to help to identify which individuals with neurological impairment might benefit from using Keeogo™ dermoskeleton, together with new information quantifying its functional benefit to the user. Implications for Rehabilitation Keeogo™ is a user-initiated dermoskeleton that has been designed to assist individuals with mobility impairments to participate more effectively in activities of daily living (ADLs). Moderately impaired individuals have the greatest potential to benefit from using the device. Benefits of wearing the device include improvements in walking speed and endurance, performance on ADLs, motor control, kinetics, and postural control.

Effect of Whole-Body Vibration on Neuromuscular Activation of Leg Muscles During Dynamic Exercises in Individuals With Stroke

Liao, L-R, and Pang, MYC. Effect of whole-body vibration on neuromuscular activation of leg muscles during dynamic exercises in individuals with stroke. J Strength Cond Res 31(7): 1954-1962, 2017-This study examined the leg muscle activity during exposure to different whole-body vibration (WBV) intensities while performing various dynamic exercises in patients with chronic stroke. Thirty patients with chronic stroke performed a series of dynamic exercises under 3 conditions: (a) low-intensity WBV (peak acceleration: 0.96 units of gravity of Earth [g]), (b) high-intensity WBV (1.61 g), and (c) no WBV. Neuromuscular activation was recorded with surface electromyography (EMG) on bilateral biceps femoris (BF), vastus lateralis, tibialis anterior (TA), and gastrocnemius (GS) in both legs and was reported as EMGrms (root mean square) normalized to % maximal voluntary contraction. The EMG amplitude of all tested muscles was significantly increased by adding WBV during dynamic exercise (p ≤ 0.05). The EMG amplitude of BF, TA, and GS during exposure to high-intensity WBV was significantly greater than low-intensity WBV (p ≤ 0.05). The increase in EMG amplitude caused by WBV was exercise dependent in GS and TA (p ≤ 0.05). The EMG response to WBV in GS and BF in the affected leg was significantly greater than the corresponding muscles in the unaffected leg (p ≤ 0.05). The extent of WBV-induced muscle activity was dependent on the dynamic exercise, WBV intensity, and muscle trained among patients with chronic stroke.

Unstable Surface Improves Quadriceps:Hamstring Co-contraction for Anterior Cruciate Ligament Injury Prevention Strategies

Background:

Increasing quadriceps:hamstring muscular co-contraction at the knee may reduce the risk of anterior cruciate ligament (ACL) injury. The purpose of this investigation was to examine muscle activation in the quadriceps and hamstrings and peak kinematics of the knee, hip, and trunk when performing a single-leg drop (SLD) on to a Bosu ball (unstable surface) compared with on to the floor (stable surface).

Hypotheses:

(1) The SLD on an unstable surface would lower the quadriceps to hamstrings electromyographic (EMG) activation ratio (Q:H EMG activation ratio) compared with being performed on the floor. (2) Lower Q:H EMG activation ratio would be caused by a relative increase in hamstring activation, with no significant change in quadriceps activation.

Study Design:

Controlled laboratory study.

Methods:

Thirty-nine Division I National Collegiate Athletic Association (NCAA) female athletes performed 3 SLDs per leg onto a Bosu ball and onto the floor. Muscle activity of the vastus lateralis and lateral hamstrings were used to estimate peak quadriceps and hamstring activation, along with the Q:H EMG activation ratio. Kinematic measures at the knee, hip, and trunk were also estimated. Differences between landings were assessed using a 2-level analysis of variance (limb and surface).

Results:

The maximum Q:H EMG activation ratio was significantly reduced when athletes performed an SLD onto the Bosu ball (20%, P < 0.001) compared with the floor. Peak hamstring activity was higher when athletes landed on a Bosu ball (18% higher, P = 0.029) compared with when they landed on the floor.

Conclusion:

Compared with landing on the floor (a stable surface), landing on a Bosu ball (unstable surface) changed the athlete’s co-contraction at the knee and increased hamstring activity. However, landing on a Bosu ball also decreased the athlete’s knee flexion, which was an undesired effect.

Clinical Relevance:

These findings highlight the potential utility of unstable surfaces as a training tool to reduce the risk of ACL injury in female athletes.