In-phase Coordination Research Articles

Patterns of change in propulsion force and late braking force in patients with stroke walking at comfortable and fast speeds

Increased propulsion force (PF) in the paretic limb is associated with improved walking speed in patients with stroke. However, late braking force (LBF), an additional braking force occurring between PF onset and toe-off, is present in a subset of stroke patients. Few studies have investigated the changes in LBF and walking speed in these patients. This study aimed to elucidate the patterns of change in PF and LBF during fast gait in hemiplegics and identify potential compensatory strategies based on the LBF patterns. Data from 100 patients with stroke walking at both comfortable (mean, 0.79 ± 024 m/s) and fast speeds (mean, 1.06 ± 0.35 m/s) were analyzed retrospectively stroke using a 3D motion analyzer. PF was higher during fast-speed walking than that during comfortable-speed walking in all patients, while LBF showed both decreasing and increasing trends during fast-speed walking. In the LBF increasing pattern, a reduction in in-phase coordination of the shank and foot during the pre-swing phase was observed, along with an increase in pelvic hike during fast-speed walking compared to those in the decreasing LBF pattern. Our findings demonstrate that alterations in LBF patterns are associated with gait deviations in patients with stroke at fast speeds.

Lower-limb inter-joint coordination during balance recovery after trips

BackgroundTrips are one of the most common external perturbations that can lead to accidental falls. Knowledge about postural control attributes of balance recovery after trips could help reveal the biomechanical causes for trip-induced falls and provide implications for fall prevention interventions. Research questionThe objective of the present study was to examine coordinated lower-limb movements during balance recovery after trips. MethodsOne hundred and twenty-three volunteers participated in an experimental study. They were tripped unexpectedly by a metal pole when walking on a linear walkway at their self-selected speed. Lower-limb inter-joint coordination quantified by continuous relative phase measures, including the mean of the absolute relative phases (MARP) and the deviation phase (DP), was analyzed during the execution of the first recovery step after unexpected trips. ResultsCompared to unsuccessful balance recovery, smaller MARPknee-ankle and DPknee-ankle of successful recovery were observed with distal inter-joint coordination on the swing side. Inter-joint coordination of the stance limb did not significantly differ between successful and unsuccessful recovery conditions. These findings indicate that the control of the swing limb’s distal joints is crucial for regaining balance after trips. SignificanceAn implication derived from this study is that greater in-phase coordination and smaller coordination variability in distal joints of the swing limb could be considered as potential targets for interventions aimed at preventing trip-induced accidental.

Differences in Lower-Extremity Joint Coordination During Two Landing Phases of a Drop Jump Task.

The aim of the present study was to compare the differences in joint coordination patterns and variability in the lower extremity between the first and second landing phases of the drop jump. Eighteen resistance-trained men (age: 22.8 ± 1.8years) performed drop jumps from a height of 0.40m. An eight-camera motion capture system was utilized to record kinematic trajectories. Modified vector coding technique and circular statistics were used to determine the coordination pattern and variability of the following joint couples during the first and second landings: hip frontal-knee frontal (HfKf), hip sagittal-knee frontal (HsKf), hip sagittal-knee sagittal (HsKs), knee frontal-ankle frontal (KfAf), knee sagittal-ankle frontal (KsAf), and knee sagittal-ankle sagittal (KsAs). Statistical differences in the distribution frequencies of coupling angles and variability between the dominant and nondominant limbs across the two landing phases were compared using two-way repeated analysis of variance and Wilcoxon rank-sum tests. During the second landing phase, the proportion of HsKs, KfAf, and KsAs showing in-phase coordination was reduced but the proportion of KfAf and KsAs showing proximal joint (knee) coordination was increased (p < .05). Significant differences in bilateral asymmetry were observed only for the HfKf and KfAf patients (p < .05). HsKs, KfAf, and KsAf varied considerably during the second landing phase (p < .05). Joint coordination patterns during the second landing phase of the drop jump differed considerably from those during the first landing phase, thereby increasing the risk of knee and ankle injuries.

Inter-Segment Coordination of Male and Female Collegiate Ice Hockey Players During Forward Skating Starts

ABSTRACT Purpose: Coordination in ice hockey skating has been minimally investigated, particularly in females. The objective was to compare lower-extremity inter-segment coordination of collegiate male and female ice hockey players during forward skating starts. Methods: 3D kinematic data were collected on collegiate male (n = 9) and female (n = 10) participants during accelerative steps. Continuous relative phase (CRP) was calculated for shank-sagittal/thigh-sagittal, shank-sagittal/thigh-frontal, and foot-sagittal/shank-sagittal segment pairs across 2.5 strides on each side. Principal component analysis (PCA) extracted features of greatest variability of the CRP and relationships between principal components and sex were investigated using hierarchical linear model. Results: Males demonstrated more out-of-phase coordination (higher CRP) for side one (p = .01) and side two (p < .01) shank-sagittal/thigh-sagittal as well as side one shank-sagittal/thigh-frontal (p < .01) segment pairs throughout each step. Females demonstrated a greater change in CRP from late stance/early swing to late swing/early stance on side two for shank-sagittal/thigh-frontal segments (p < .01). For side two shank-sagittal/thigh-frontal segments, faster males utilized more out-of-phase coordination throughout each step whereas faster females utilized more in-phase coordination (p < .01). Conclusion: Males and females may employ different coordinative strategies to achieve faster skating speeds. Males tend to utilize more out-of-phase coordination of the shank and thigh throughout strides, although coordinative differences of the shank and foot were not found between sexes. Further investigation is needed to examine the relationship between lower limb strength and coordination as well as the effect of targeted training protocols on lower extremity coordinative patterns.

Follow the Leader: Parent- and Child-led Synchrony in Competitive and Cooperative play

Social interactions involve both cooperation to achieve a shared goal and competition over shared resources and rewards. The ability to engage in inter-personal coordination is an important measure of socio-emotional and cognitive well-being. Both cooperation and competition require interpersonal coordination, however with different motivational backgrounds. Competition is defined by a higher level of extrinsic motivation, while cooperation is related to more intrinsic motivation. In the context of the parent-child dyad, each individual has different motivations and contributions to the dyad. The parent’s and child’s sense of competitiveness and contribution to inter-personal synchrony will presumably differ from each other and adapt to one another. The current research employed Motion Energy Analysis, an objective measure of coordination of movements between individuals, to measure motor in-phase and anti-phase synchrony during parent-child cooperative and competitive play, with a focus on parent and child-led synchrony. Findings highlight that parents rate themselves as less competitive than their children rate themselves; with no such difference noted in cooperation. Further, parent-led motor synchrony is defined more by in-phase coordination in competition, especially when the interaction is novel. Alternatively, child-led motor synchrony is more anti-phase during competition. In cooperation parents and children lead synchrony to the same extent and in the same phase. Current findings highlight that parent’s and children uniquely adjust their leading behaviors in synchrony in competition, presumably adjusting their behavior to accommodate a complex situation. Given the importance of cooperative and competitive interactions to overall social well-being, and the parent’s role of modeling behaviors for their child, findings may direct future guidance and treatment plans that will promote social development.

Exploring pelvis and thigh movement and coordination patterns during walking in patients after total hip arthroplasty

BackgroundPatients after total hip arthroplasty (THA) have altered hip kinematics compared to healthy controls, specifically hip extension and range of motion are lower. Exploring pelvis-thigh coordination patterns and coordination variability may help to elucidate why differences in hip kinematics are evident in patients following THA. Research QuestionDo sagittal plane hip, pelvis and thigh kinematics, and pelvis-thigh movement coordination and coordination variability differ between patients following THA and healthy controls during walking? MethodsSagittal plane hip, pelvis and thigh kinematics were collected using a three-dimensional motion capture system while 10 patients who had undergone THA and 10 controls walked at a self-selected pace. A modified vector coding technique was used to quantify pelvis-thigh coordination and coordination variability patterns. Peak hip, pelvis and thigh kinematics and ranges of motion, and movement coordination and coordination variability patterns were quantified and compared between groups. ResultsPatients after THA have significantly (p ≤ .036; g ≥ 0.995) smaller peak hip extension and range of motion, and peak thigh anterior tilt and range of motion compared to controls. Additionally, patients following THA have significantly (p ≤ .037; g ≥ 0.646) more in-phase distally and less anti-phase distally dominated pelvis-thigh movement coordination patterns compared to controls. SignificanceThe smaller peak hip extension and range of motion displayed by patients following THA is due to smaller peak anterior tilt of the thigh, which in turn limits thigh range of motion. The lower sagittal plane thigh, and in turn hip, motion used by patients after THA may be due to increases in the in-phase coordination of pelvis-thigh motion patterns, which cause the pelvis and thigh to work as a singular functional unit.

Effects of aging on arm coordination at different walking speeds

BackgroundPrevious work has shown that the mean continuous relative phase and coordination variability of lower limbs are modified in older adults when walking. Research questionHere, we propose to understand the extent to which such control mechanisms for upper limbs are present during gait. Specifically, we seek to understand if aging and gait speed constraints influence the interjoint control of upper limbs during walking. MethodsThis observational study evaluated thirty-three participants, divided into older (n = 20, age 66.4 ± 4.3 years; mass: 77.2 ± 14.2 kg; height: 165 ± 9.20 cm) and young adults (n = 13, age 29.5 ± 4.7 years; mass 75.5 ± 9.6 kg; height: 172 ± 6.24 cm) were asked to walk at 0.28, 0.83, 1.38 m.s−1 on a level treadmill while their segmental movements were simultaneously registered with 3D motion capture system. We calculated the mean continuous relative phase and coordination variability (continuous relative phase variability) in elbow-shoulder and shoulder-hip pairs, and a generalized estimating equation was used to test the main and interaction effects of age and speed. ResultsOlder adults had a reduced continuous relative phase (more in-phase coordination) of upper limbs at whole stance for elbow-shoulder, at loading response for shoulder-hip, at mid-stance and terminal stance for elbow-shoulder and shoulder-hip in comparison to young adults at different speeds (p < 0.05). The coordination variability of upper limbs was greater (higher continuous relative phase variability) in older than young adults at 0.28 and 1.38 m.s−1. SignificanceThese findings substantiate the altered motor control role of upper limbs in gait aging, suggesting that lower self-selected speed may be related to the reduced ability to control arm movement during the intermediate phases of gait.

The effect of changes in saddle height on coordination and its variability during pedalling cycle

ABSTRACT Modifications in saddle height affect the range of movement of the lower limb’s joints during pedalling. Although its effect on movement patterns is poorly understood. The purpose of this study was to analyse the acute effects of small changes in bicycle saddle height on pedalling coordination and its variability. Lower extremity kinematic data were collected in random order for ten well-trained cyclists while pedalling at three different saddle heights: preferred, 2% higher and 2% lower than preferred position. A dynamical systems approach was used to quantify the coordination and its variability for selected joint couplings. Modifications in saddle height produced large changes in the frequency of movement patterns, although they were not enough to alter the coordination classification. Lowering the saddle height increased the frequency of the proximal coordinative hip-ankle pattern (F = 11.77, p < .01) and knee-ankle couplings (F = 14.39, p < .01), while decreasing inphase coordination (F > 11.03, p < .01) during the propulsive phase. Pedalling coordination variability was not affected, being greatest during the movement transitions and when the ankle joint was included in the coupling. This study demonstrated that pedalling pattern coordination and coordination variability were generally stable to acute small changes in saddle height in well-trained cyclists.

The relationship between insulin and glucagon concentrations in non-diabetic humans.

Abnormal postprandial suppression of glucagon in Type 2 diabetes (T2DM) has been attributed to impaired insulin secretion. Prior work suggests that insulin and glucagon show an inverse coordinated relationship. However, dysregulation of α‐cell function in prediabetes occurs early and independently of changes in β‐cells, which suggests insulin having a less significant role on glucagon control. We therefore, sought to examine whether hepatic vein hormone concentrations provide evidence to further support the modulation of glucagon secretion by insulin. As part of a series of experiments to measure the effect of diabetes‐associated genetic variation in TCF7L2 on islet cell function, hepatic vein insulin and glucagon concentrations were measured at 2‐minute intervals during fasting and a hyperglycemic clamp. The experiment was performed on 29 nondiabetic subjects (age = 46 ± 2 years, BMI 28 ± 1 Kg/m2) and enabled post‐hoc analysis, using Cross‐Correlation and Cross‐Approximate Entropy (Cross‐ApEn) to evaluate the interaction of insulin and glucose. Mean insulin concentrations rose from fasting (33 ± 4 vs. 146 ± 12 pmol/L, p < 0.01) while glucagon was suppressed (96 ± 8 vs. 62 ± 5 ng/L, p < 0.01) during the clamp. Cross‐ApEn was used to measure pattern reproducibility in the two hormones using glucagon as control mechanism (0.78 ± 0.03 vs. 0.76 ± 0.03, fasting vs. hyperglycemia) and using insulin as a control mechanism (0.78 ± 0.02 vs. 0.76 ± 0.03, fasting vs. hyperglycemia). Values did not differ between the two scenarios. Cross‐correlation analysis demonstrated a small in‐phase coordination between insulin and glucagon concentrations during fasting, which inverted during hyperglycemia. This data suggests that the interaction between the two hormones is not driven by either. On a minute‐to‐minute basis, direct control and secretion of glucagon is not mediated (or restrained) by insulin.

Movement Coordination during Functional Single-Leg Squat Tests in Healthy, Recreational Athletes

The single-leg squat (SLS) represents a functional movement task for determining leg function. Objective movement analysis is required to evaluate inter-limb symmetry and movement coordination. Therefore, this study aimed to investigate inter-limb symmetry of SLS kinematics and movement coordination using the modified vector coding technique. A 3D motion capture system and electromyography were used to assess SLS execution and muscle activation of hip ab- and adductors of 17 healthy, recreational athletes. Coordination patterns of hip, knee, and ankle joint movement were assessed by the modified vector coding technique. Statistical parametric mapping revealed no significant differences between both legs (p &gt; 0.05). Inter-limb symmetry also appeared in movement coordination (p &gt; 0.05). Additionally, the analysis of movement coordination indicates knee-dominant, in-phase coordination. However, coordination patterns were different between downward movement, change of direction, and upward movement (p &lt; 0.001). Since perturbations during SLS execution, such as moments of imbalance, occur as anti-phase coordination patterns, the analysis of coordination patterns can be used as a new evaluation method for SLS performance. Furthermore, the modified vector coding technique might be helpful to analyze different compensation strategies during the SLS in symptomatic individuals.

Head control and head-trunk coordination as a function of anticipation in sidestepping

ABSTRACT Head reorientation precedes body reorientation during direction change to facilitate gaze realignment, thus enhancing perceptual awareness. Whole body kinematics are dependent on the available planning time. The purpose of this study was to assess the role of anticipation on head control and head-trunk coordination during sidestepping tasks. Fourteen male collegiate athletes performed anticipated and unanticipated sidestepping tasks. Transverse plane head, trunk and heading direction, as well as head-trunk coordination were assessed. During change of direction tasks, we observed greater head orientation towards the new travel direction, followed by heading direction and then trunk direction during both anticipated and unanticipated tasks. With reduced planning time, heading in the preparatory phase and trunk rotation in the preparatory and stance phases were significantly less oriented towards the new travel direction, with no differences in head rotation. During anticipated sidestepping, significantly greater in-phase coordination was observed during the preparatory phase compared to unanticipated sidestepping. Head reorientation facilitates gaze realignment and may be prioritized irrespective of planning time during sidestepping tasks. During anticipated trials, the head and trunk move more synchronously compared to unanticipated sidestepping, highlighting the potential benefits of aligning the degrees of freedom earlier in the change of direction stride and optimizing perceptual awareness.

Influence of back muscle fatigue on dynamic lumbar spine stability and coordination variability of the thorax-pelvis during repetitive flexion–extension movements

Previous work has identified that individuals adopt different dynamic lumbar spine stability responses when experiencing back muscle fatigue, and that the neuromuscular system adjusts multi-joint coordination in response to fatigue. Therefore, this study was designed to determine whether distinct differences in coordination and coordination variability would be observed for those who stabilize, destabilize, or demonstrate no change in dynamic stability when their back muscles are fatigued. Thirty participants completed two repetitive trunk flexion–extension trials (Rested, Fatigued) during which lumbar flexion–extension dynamic stability, thorax-pelvis movement coordination, and coupling angle variability (CAV) were assessed. Dynamic stability was evaluated using maximum Lyapunov exponents (λmax) with participants being allotted to stabilizer, destabilizer, or no change groups based on their stability response to fatigue. Each flexion–extension repetition was further segregated into two phases (flexion, extension) and vector coding analyses were implemented to determine thorax-pelvis coordination and CAV during each movement phase. Results demonstrated that when fatigued, ∼30% of individuals adopted more stable (lower λmax) flexion–extension movements and greater CAV during the extension phase, ∼17% of individuals became less stable (higher λmax) and exhibited decreased CAV during the extension phase, and the remaining ∼53% of individuals expressed no change in dynamic stability or CAV. Additionally, more in-phase coordination patterns were generally observed across all individuals when fatigued. Altogether, this study highlights the heterogeneous nature of lumbar spine movement behaviours within a healthy population in response to fatigue.

Inter-limb coupling in individuals with transtibial amputation during bilateral stance is direction dependent.

We investigated the control of upright standing in individuals with unilateral transtibial amputation (TTA) by assessing the inter-limb coupling and the coupling between the center of pressure beneath both limbs combined (COPNET) and the center of pressure (COP) beneath the prosthetic limb and the intact limb. Twenty-one adults with TTA and eighteen unimpaired adults completed 90s of standing on two parallel force plates. The inter-limb coupling and the coupling between the COP beneath each limb and the COPNET were assessed by quantifying the synchronization of the COP signals. This included the number of epochs with synchronized signals, the total duration of signal synchronization and the relative phase and deviation phase between the signals. Additionally, magnitude and temporal characteristics of the COP displacements were quantified. Individuals with TTA exhibited looser inter-limb coupling in the anterior-posterior direction, characterized by more shifts between epochs with synchronized signals, shorter total duration of signal synchronization, less in-phase coordination patterns and a higher deviation phase between the two limbs, compared to unimpaired individuals. This coincided with a larger and more irregular postural sway in the TTA group. No group difference was observed in the mediolateral direction. The coupling between the COPNET and the COP beneath the individual limbs was similarly direction dependent, and tighter for the intact side, suggesting that an intact limb-driven strategy was utilized.

The impact of outdoor walking surfaces on lower-limb coordination and variability during gait in healthy adults

BackgroundInter-joint coordination and variability during gait provide insight into control and adaptability of the neuromuscular system. To date, coordination research has been restricted to laboratory settings, and it is unclear how these findings translate to real-world, outdoor walking environments. Research QuestionCompared to flat walking, to what extent do outdoor surfaces impact lower-limb inter-joint coordination and variability during gait, in healthy adults? MethodsData from inertial measurement units placed on the lower-back, thigh, and shank were extracted from thirty healthy young adults (15 females, 23.5 ± 4.2 years) during outdoor walking on flat (paved sidewalk); irregular (cobblestone, grass); sloped (slope-up, slope-down); and banked (banked-right, banked-left) surfaces. Sagittal joint angles for the right knee and hip were computed and partitioned by gait phase (stance and swing). Continuous Relative Phase analysis determined inter-joint coordination and variability for the knee-hip joint pair using Mean Absolute Relative Phase (MARP) and Deviation Phase (DP), respectively. One-way repeated measures ANOVAs tested surface effects. Post-hoc Bonferroni adjusted surface comparisons were assessed. ResultsSignificant knee-hip surface effects were seen during all gait phases for MARP (p < 0.001) and DP (p ≤ 0.001). Compared to flat walking, grass prompted more in-phase coordination (smaller MARP) during stance and swing phase (p ≤ 0.003). Slope-up caused more in-phase coordination during stance (p < 0.001), while slope-down caused more out-of-phase coordination during stance and swing (p ≤ 0.003), compared to the flat surface. Sloped surfaces prompted more variable (larger DP) knee-hip coordination (p ≤ 0.001), compared to flat walking during stance and swing phase. SignificanceCompared to flat walking, changes in knee-hip coordination and variability were greatest on slope-up/slope-down surfaces. This could reflect greater changes in lower-limb kinematics on sloped surfaces and/or a neuromuscular response to the demands of a more challenging task.

Effects of limited knee flexion movement in intra-limb gait coordination

This study aimed to investigate intra-limb coordination in non-disabled individuals walking with and without a constrained knee and in individuals with stroke. We hypothesized that a constrained knee would modify the intra-limb coordination of non-disabled individuals and that non-disabled individuals walking with a constrained knee would present coordination patterns similar to those presented by individuals with stroke. Twelve individuals with chronic stroke (age: 54.1 ± 9.9 years) and 12 age- and sex-matched individuals (age: 54.8 ± 9.2 years) with no known gait impairment (non-disabled individuals) participated in this study. Non-disabled individuals walked with and without an orthosis on one of their knees, limiting flexion to 40°, which was the average maximum knee flexion presented by the participants with stroke. Lower limb coordination was assessed on the basis of vector coding for the thigh-shank and shank-foot couplings during stance and swing periods of gait. Constrained knee flexion in non-disabled individuals mainly affected the thigh-shank coupling but not the shank-foot coupling of the constrained limb. There was reduced anti-phase coordination during the stance and swing periods and a marked increase in in-phase coordination during the swing period. Non-disabled individuals presented most changes toward the coordination pattern presented by individuals with stroke, except for the thigh-phase mode during the swing period, which was lower than that in individuals with stroke. Reduced knee flexion movement caused similar alterations in the intra-limb coordination pattern in non-disabled individuals compared to those observed in individuals with stroke. Therefore, diminished knee flexion movement, which is presented by individuals with stroke, can be considered a key disturbance that leads to impairment in lower extremity intra-limb coordination.

Individuals with recurrent low back pain exhibit further altered frontal plane trunk control in remission than when in pain

BackgroundMovement alterations due to low back pain (LBP) could lead to long-term adverse consequences if they do not resolve after symptoms subside. This study aims to determine if altered trunk control associated with recurrent low back pain persists beyond symptom duration. MethodsTwenty young adults with recurrent LBP were tested once during an LBP episode and once in symptom remission, and twenty matched back-healthy participants served as controls. Participants walked on a treadmill with five prescribed step widths (0.33, 0.67, 1, 1.33, 1.67 × preferred step width). Motion capture and surface electromyography were used to record trunk kinematics and muscle activation. Thorax-pelvis coordination was calculated using vector coding, and longissimus activation and co-activation were analyzed. FindingsYoung adults with recurrent LBP exhibited a “looser” trunk control strategy in the frontal plane during gait that was persistent regardless of pain status across multiple step widths compared to controls. The looser trunk control was demonstrated by a greater pelvis-only, less thorax-only coordination pattern, and decreased bilateral longissimus co-activation in individuals with recurrent LBP compared to controls. The looser trunk control strategy was further amplified when individuals were in symptom remission and exhibited greater trunk excursion and reduced in-phase coordination in the frontal plane. InterpretationThe amplification of aberrant movement during symptom remission may suggest that movement patterns or anatomical factors existing prior to the tested painful episode underlie altered trunk control in individuals with recurrent LBP. The symptom remission period of recurrent LBP may be a critical window into clinical evaluation and treatment.

Effects of back-support exoskeleton use on trunk neuromuscular control during repetitive lifting: A dynamical systems analysis

Back-support exoskeletons (BSEs) are a promising ergonomic intervention to mitigate the risk of occupational low back pain. Although growing evidence points to the beneficial effects of BSEs, specifically in reducing low-back physical demands, there is limited understanding of potential unintended consequences of BSE use on neuromuscular control of the trunk during manual material handling (MMH). We quantified the effects of two passive BSEs (BackX™ AC and Laevo™ V2.5) on trunk dynamic stability and movement coordination during a repetitive lifting task. Eighteen participants (gender-balanced) completed four minutes of repetitive lifting in nine different conditions, involving symmetric and asymmetric postures when using the BSEs (along with no BSE as a control condition). Maximum Lyapunov exponents (short-term: λmax-s; long-term: λmax-l) and Floquet multipliers (FMmax) were respectively calculated to quantify the local dynamic and orbital stability of thorax and pelvis trajectories. Thorax-pelvis segmental coordination was also quantified using the continuous relative phase. Wearing the Laevo™ significantly increased λmax-s for the pelvis (by ~ 8%) and FMmax for the thorax and pelvis (by ~ 5–10%). Use of either BSE decreased the in-phase coordination pattern for the thorax-pelvis coupling (by ~ 15%). These results suggest that BSE use can compromise neuromuscular control of the trunk, and caution should thus be used in selecting a suitable BSE for use in a given MMH task. Future work is needed, however, to assess the generalizability of different BSE design approaches in terms of unintended short-term and long-term effects on trunk neuromuscular control.

The effect of inherent and incidental constraints on bimanual and social coordination

The current investigation was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with bimanual and social coordination. Individual participants (N = 9) and pairs of participants (N = 18, 9 pairs) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multi-frequency patterns by exerting force with their right and left limbs. Lissajous information was provided to guide performance. Participants performed 13 practice trials and 1 test trial per pattern. On the test trial, muscle activity from the triceps brachii muscles of each arm was recorded. EMG-EMG coherence between the two EMG signals was calculated using wavelet coherence. The behavioral data indicated that individual participants performed the 1:1 in-phase pattern more accurately and with less variability than paired participants. The EMG coherence analysis indicated significantly higher coherence for individual participants than for the paired participants during the 1:1 in-phase pattern, whereas no differences were observed between groups for the 1:2 coordination pattern. The results of the current investigation support the notion that neural crosstalk can stabilize 1:1 in-phase coordination when contralateral and ipsilateral signals are integrated via the neuromuscular linkage between two effectors.

Intra-trunk and arm coordination displayed by Olympic rowing athletes

ABSTRACT The purpose was to assess the intra-trunk and arm coordination of Olympic athletes during rowing on an ergometer. Rowing was performed at three stroke rates (18, 26, and 32 strokes/min). The sagittal plane motions of trunk segments and upper arm were collected for 59 Olympic athletes (32 females and 27 males) from the Chinese National Rowing Team. The coupling angles between the three pairs of segments (lumbar-pelvis, thorax-lumbar, upper arm-thorax) were generated using a vector coding method. The coupling angles were classified: in-phase, anti-phase, superior-phase, and inferior-phase. Three-way, mixed-model ANOVA were used to test the time spent in each coordination pattern. The trunk segments and upper arms demonstrated an in-phase coordination pattern for most of the time. During the drive phase, the time spent in in-phase was increased at higher stroke rates. Athletes are encouraged to use this in-phase pattern, especially between the pelvis and lumbar spine during training with high demands of stroke repetitions or time. During the recovery phase, the trunk segments were rotating mostly in-phase whereas the upper arm was flexing dominantly to maintain stroke length at higher stroke rates. Female and male rowers exhibited similar intra-trunk coordination patterns except for the upper arm-thorax pair.

Trunk-pelvic coordination during unstable sitting with varying task demand: A methodological study

Unstable sitting is used commonly to evaluate trunk postural control (TPC), typically via measures based on center-of-pressure (CoP) time series. However, these measures do not directly reflect underlying control/movement strategies. We quantified trunk-pelvis coordination during unstable sitting using vector coding (VC) and correlated such coordination with CoP-based outcomes across varying task demands. Thirteen uninjured individuals (11 male/2 female) sat on an unstable chair at four instability levels, in a random order, defined relative to the individual gravitational gradient (∇G): 100, 75, 60, and 45%∇G. VC assessed trunk-pelvic coordination, and coupling angles classified movements as: 1) anti-phase, 2) in-phase, 3) trunk-phase, or 4) pelvic-phase. With decreasing %∇G (i.e., increasing instability), we found: increased anti-phase movement in the sagittal and frontal planes; decreased in-phase movement in the sagittal and frontal planes; and increased in-phase and pelvic-phase movement in the transverse plane. In the sagittal and frontal planes, we observed significant weak-to-moderate correlations between anti-phase and in-phase movements (0.288 < |ρ| < 0.549). Correlations between CoP-based measures and pelvic-phase and trunk-phase movements were typically weak and/or non-significant (|ρ| < 0.318). VC techniques discriminated between levels of instability during unstable sitting, identifying in-phase coordination (stiffening strategy) at lower instability levels and anti-phase coordination at higher instability levels. Compared to CoP-based measures, trunk coordination outcomes during unstable sitting provide measures of TPC that more directly quantify underlying movement strategies. These results can also serve as a baseline for future work investigating populations with impaired TPC (e.g., individuals with low back pain or limb loss).