The Effect of Virtual Reality on Gait Variability

Optic Flow (OF) plays an important role in human locomotion and manipulation of OF characteristics can cause changes in locomotion patterns. The purpose of the study was to investigate the effect of the velocity of optic flow on the amount and structure of gait variability. Each subject underwent four conditions of treadmill walking at their self-selected pace. In three conditions the subjects walked in an endless virtual corridor, while a fourth control condition was also included. The three virtual conditions differed in the speed of the optic flow displayed as follows – same speed (OFn), faster (OFf), and slower (OFs) than that of the treadmill. Gait kinematics were tracked with an optical motion capture system. Gait variability measures of the hip, knee and ankle range of motion and stride interval were analyzed. Amount of variability was evaluated with linear measures of variability - coefficient of variation, while structure of variability i.e., its organization over time, were measured with nonlinear measures - approximate entropy and detrended fluctuation analysis. The linear measures of variability, CV, did not show significant differences between Non-VR and VR conditions while nonlinear measures of variability identified significant differences at the hip, ankle, and in stride interval. In response to manipulation of the optic flow, significant differences were observed between the three virtual conditions in the following order: OFn \u3e OFf \u3e OFs. Measures of structure of variability are more sensitive to changes in gait due to manipulation of visual cues, whereas measures of the amount of variability may be concealed by adaptive mechanisms. Visual cues increase the complexity of gait variability and may increase the degrees of freedom available to the subject. Further exploration of the effects of optic flow manipulation on locomotion may provide us with an effective tool for rehabilitation of subjects with sensorimotor issues

Age induced modifications in the persistency of voluntary sway when actively tracking the complex motion of a visual target

Movement persistency, reflected in systematic cycle to cycle fluctuations of a rhythmical task such as walking or voluntary sway, is compromised with increasing age, making older adults more susceptible to falls. In the present study, we tested whether it is possible to improve rhythmic voluntary sway persistency in old age by actively tracking the complex (i.e. persistent) motion of a visual target. Twenty healthy young and 20 older adults performed 132 cycles of anterior-posterior sway under two conditions: a) self-paced sway and b) sway while tracking the vertical motion of a complex visual target. The persistency of sway cycle amplitude and duration, detected from the center of pressure displacement, was quantified using the Fractal exponent α. We also recorded body kinematics in order to assess the intersegmental coordination that was quantified in the Mean Absolute Relative Phase (MARP) and the Deviation Phase (DPh) between the trunk and the lower limbs. In self-paced sway, older adults showed a lower persistency of cycle duration and a higher MARP and DPh between the trunk and the lower limbs compared to young adults. Tracking the complex visual target motion increased the persistency of cycle amplitude, in young but not in older adults, when compared to the self-paced sway while it decreased the persistency of cycle duration in both groups. The relative phase measures showed a moderate to strong relationship with the persistency of cycle amplitude and duration when older adults swayed in their self-pace. These findings suggest older adults cannot exploit active tracking of the complex visual motion cue to improve voluntary sway persistency. This could be related to the less stable and out of phase intersegmental coordination characterizing rhythmic voluntary sway in old age

Variability of Lower Extremity Joint Kinematics During Backward Walking in a Virtual Environment

Backward walking (BW) shows significant differences with forward walking (FW) and these differences are potentially useful in rehabilitation. However the lack of visual cues makes BW risky. The purpose of this study was to investigate the effect of visual cues provided by a virtual environment on FW and BW on gait variability. Each subject underwent four conditions of treadmill walking at self-selected pace. The subjects walked backwards in three conditions and forwards in the fourth condition. A virtual corridor was displayed to the subjects in the FW condition (forward optic flow) and two of the backward conditions (forward and backward optic flow). The third BW condition was a control condition (no visual cues). Gait variability measures of the hip, knee and ankle range of motion and the stride interval were analyzed. Magnitude of variability was evaluated with the coefficient of variation and structure of variability with approximate entropy. Significant differences were demonstrated between the FW and the BW gait characteristics as well as in gait variability (for both magnitude and structure of variability). No significant differences were found between the three BW conditions as a result of the direction of visual cues. In order to get optimal benefit of BW in the aged and the diseased, optical flow of visual feedback may need to be manipulated in a different manner than FW. Future studies will explore other parameters of visual cues like the velocity of optic flow and appearance of obstacles to obtain the best visual cue configuration for rehabilitation

Swaying to the complex motion of a visual target affects postural sway variability

Background Voluntary shifting body weight in the anteroposterior direction is an important element of daily life activities, such as rising from a chair or initiating a step. In order to accommodate the daily-life challenges of such tasks, voluntary postural sway needs to be flexible and variable. Research question In this study we asked how whole-body tracking of a complex visual target motion with the concurrent provision of feedback modulates the variability of voluntary sway. Methods Twenty young adults (age: 27.10 ± 9.15years, height: 170.73 ± 9.40 cm, mass: 62.84 ± 11.48 kg) performed 132 cycles of voluntary antero-posterior sway, on a force platform, under two conditions: a) self-paced sway and b) swaying while tracking the complex motion of a visual target. Magnitude and temporal structure of variability of postural sway were investigated with the Coefficient of Variance (CoV) and the fractal exponent α, respectively. This analysis was performed for sway cycle duration, amplitude and velocity. The cross-correlation function between the target and sway cycle parameters was computed as a measure of visuo-postural coupling. Results The CoV of sway cycle amplitude, duration and velocity increased during active tracking of the complex target. Fractal exponent α increased for sway cycle amplitude but decreased for cycle duration and remained unchanged for sway velocity. The cross-correlation function revealed a consistent peak at lag+1 indicating an asynchrony between the target and sway cycle duration, while the peak cross-correlation for cycle amplitude was noted at lag 0. Significance Swaying to the complex motion of a visual target improves the variability of sway cycle amplitude, at the cost of cycle duration. This is associated with a more synchronous spatial than temporal coupling to the visual target motion. This knowledge could inform the design of postural tracking paradigms as appropriate exercise interventions, for improving voluntary sway in populations with reduced limits of stability (i.e. older adults)

Razvoj grčkog ribarstva tijekom razdoblja 1928. -1939.

In the present study, Greek fisheries landings were extended back to 1928, for the first time, from data derived by the General Statistical Service of Greece during the 1928-1939 period. In particular, we: (a) present the annual fisheries landings for all species combined, fishing effort for all gear-types combined and species-specific landings during 1928-1939, (b) re-allocate the spatial resolution of landings during 1928-1939 to that during 1964-2007, and (c) compare the landings for different periods during 1928-2007. Results showed that during 1928-1939, landings and effort generally increased. The time series of all species landings exhibited a strong between-year variability, with 23 out of 40 species displaying a significant increasing trend. The analysis of fisheries landings over time (1928-2007) displayed four distinct patterns corresponding to four phases of Greek fisheries development: (1) a gradual increase during 1928-1949 (pre-development phase of fisheries), (2) a steeper increase during 1950-1969 (growth phase), (3) a much steeper linear increase during 1970-1994 (fully tο over-exploited phase) and (4) a declining trend during 1995-2007 (collapse phase). These phases coincided chronologically with significant socio-economic and political events that took place in Greece since 1928.U ovom radu, po prvi put, je iznesen status ulova u grčkom ribarstvu i to u razdoblju od 1928. do 1939. godine prema podacima iz Opće statističke službe u Grčkoj. Konkretno, izneseno je slijedeće: a) predstavljen je godišnji ulov ribarstva za sve vrste zajedno, ribolovni napor za sve vrste alata u kombinaciji i vrste specifičnih ulova tijekom razdoblja 1928.-1939., b) ponovno dodijeljive prostorne rezolucije ulova tijekom 1928.-1939., te tijekom 1964.-2007., i c) uspoređen je ulov za različita razdoblja tijekom 1928.-2007. Rezultati su pokazali da su se tijekom 1928.-1939., ulov i ribolovni napor općenito povećali. Vremenske serije svih vrsta ulova su bile izložene jakim međugodišnjim varijabilnostima, te od 40 vrsta njih 23 su pokazale značajan trend rasta. Analiza ukupnog ulova ribarstva tijekom vremena (1928.-2007.) prikazuje četiri različita uzoraka koji obilježavaju četiri faze razvoja grčkog ribarstva: 1. postupno povećavanje tijekom 1928.-1949. (pred-faza razvoja ribarstva), 2. strmo povećanje tijekom 1950.-1969. (faza rasta), 3. značajan linearni porast tijekom 1970.-1994. (faza potpunog dο prekomjernog ulova) i 4. opadajući trend tijekom 1995.-2007. (kolaps faza). Ove faze se kronološki poklapaju sa značajnim socio-ekonomskim i političkim događanjima koja su se zbivala u Grčkoj od 1928. godine

The Influence of Visual Perception of Self-Motion on Locomotor Adaptation to Unilateral Limb Loading

Self-perception of motion through visual stimulation may be important for adapting to locomotor conditions. Unilateral limb loading is a locomotor condition that can improve stability and reduce abnormal limb movement. In the present study, the authors investigated the effect of self-perception of motion through virtual reality (VR) on adaptation to unilateral limb loading. Healthy young adults, assigned to either a VR or a non-VR group, walked on a treadmill in the following 3 locomotor task periods—no load, loaded, and load removed. Subjects in the VR group viewed a virtual corridor during treadmill walking. Exposure to VR reduced cadence and muscle activity. During the loaded period, the swing time of the unloaded limb showed a larger increase in the VR group. When the load was removed, the swing time of the previously loaded limb and the stance time of the previously unloaded limb showed larger decrease and the swing time of the previously unloaded limb showed a smaller increase in the VR group. Lack of visual cues may cause the adoption of cautious strategies (higher muscle activity, shorter and more frequent steps, changes in the swing and stance times) when faced with situations that require adaptations. VR technology, providing such perceptual cues, has an important role in enhancing locomotor adaptation

Electromechanical Delay of the Knee Flexor Muscles Is Impaired After Harvesting Hamstring Tendons for Anterior Cruciate Ligament Reconstruction

Background Changes in electromechanical delay during muscle activation are expected when there are substantial alterations in the structural properties of the musculotendinous tissue. In anterior cruciate ligament reconstruction, specific tendons are being harvested for grafts. Thus, there is an associated scar tissue development at the tendon that may affect the corresponding electromechanical delay. Purpose This study was conducted to investigate whether harvesting of semitendinosus and gracilis tendons for anterior cruciate ligament reconstruction will affect the electromechanical delay of the knee flexors. Study Design Case-control study; Level of evidence, 3. Methods The authors evaluated 12 patients with anterior cruciate ligament reconstruction with a semitendinosus and gracilis autograft, 2 years after the reconstruction, and 12 healthy controls. Each participant performed 4 maximally explosive isometric contractions with a 1-minute break between contractions. The surface electromyographic activity of the biceps femoris and the semitendinosus was recorded from both legs during the contractions. Results The statistical comparisons revealed significant increases of the electromechanical delay of the anterior cruciate ligament–reconstructed knee for both investigated muscles. Specifically, the electromechanical delay values were increased for both the biceps femoris (P = .029) and the semitendinosus (P = .005) of the reconstructed knee when compared with the intact knee. Comparing the anterior cruciate ligament–reconstructed knee against healthy controls revealed similar significant differences for both muscles (semitendinosus, P = .011; biceps femoris, P = .024). Conclusion The results showed that harvesting the semitendinosus and gracilis tendons for anterior cruciate ligament reconstruction significantly increased the electromechanical delay of the knee flexors. Increased hamstring electromechanical delay might impair knee safety and performance by modifying the transfer time of muscle tension to the tibia and therefore affecting muscle response during sudden movements in athletic activities. However, further investigation is required to identify whether the increased electromechanical delay of the hamstrings can actually influence optimal sports performance and increase the risk for knee injury in athletes with anterior cruciate ligament reconstructions

The effects of a plyometric training program on the latency time of the quadriceps femoris and gastrocnemius short-latency responses

Aim: The purpose of this study was to determine if a plyometric training program can affect the latency time of the quadriceps femoris and gastrocnemius short-latency responses (SLRs) of the stretch reflex. Methods: Sixteen healthy subjects (12 female and 4 male) were randomly assigned to either a control or a plyometric training group. Maximum vertical jump height (VJ) and SLRs of both quadriceps femoris and gastrocnemius were measured before and after a four week plyometric training program. Results: Plyometric training significantly increased VJ (mean+/-SEM) by 2.38+/-0.45 cm (P\u3c0.05) and non-significantly decreased the latency time of the quadriceps femoris SLR (mean+/-SEM) 0.363+/-0.404 ms (P\u3e0.05) and gastrocnemius SLR (mean+/-SEM) 0.392+/-0.257 ms (P\u3e0.05). VJ results support the effectiveness of plyometric training for increasing VJ height. Conclusions:The non-significant changes in the latency time of the quadriceps femoris and gastrocnemius SLRs seen in the training group suggest that performance improvements following a four-week plyometric training program are not mediated by changes in the latency time of the short-latency stretch reflex

Electromechanical Delay of the Knee Flexor Muscles After Harvesting the Hamstrings for Anterior Cruciate Ligament Reconstruction

Objective: To investigate if harvesting of semitendinosus (ST) and gracilis for anterior cruciate ligament (ACL) reconstruction will have an effect in coordinative firing pattern of the hamstrings under fatigue. We hypothesized that fatigue will increase the electromechanical delay (EMD) of the hamstrings on the harvested site and impair the synchronization between the medial and lateral hamstrings, in terms of muscle activity onsets. Design: Prospective nonrandomized study. Setting: Institutional. Patients: Twelve ACL reconstructed patients with hamstrings, 2 years postoperatively. Interventions: The patients performed a fatigue protocol with 25 continuous maximal isometric voluntary contractions of 8-second duration with 2-second intervals. Main Outcome Measures: The electromyography activity of biceps femoris (BF) and ST was recorded bilaterally and simultaneously with the torque measurements. The dependent variable examined was the EMD difference between BF and ST (muscle activation pattern). Results: The fatigue protocol caused significant differences for the EMD values for both the intact and the reconstructed leg, demonstrating the influence of fatigue in EMD. However, the synchronization pattern between the medial and lateral hamstrings did not change significantly throughout the fatiguing protocol, revealing a balanced effect of fatigue. Conclusions: Although the EMD of ST and BF was significantly increased due to fatigue, as expected, their synchronization pattern as identified by the difference in their EMDs remained the same. Thus, the reconstructed knee responded in a balanced manner and the hamstrings firing pattern remained the same, despite the intervention to the ST tendon

Knee braces can decrease tibial rotation during pivoting that occurs in high demanding activities

Purpose The purpose of this study was to investigate whether knee braces could effectively decrease tibial rotation during high demanding activities. Methods Using an in vivo three-dimensional kinematic analysis, 21 physically active, healthy, male subjects were evaluated. Each subject performed two tasks that were used extensively in the literature because they combine increased rotational and translational loads on the knee, (1) descending from a stair and subsequent pivoting and (2) landing from a platform and subsequent pivoting under three conditions: (A) wearing a prophylactic brace (braced), (B) wearing a patellofemoral brace (sleeved), and (C) unbraced condition. Results In the first task, tibial rotation during the pivoting phase was significantly decreased in the braced condition as compared to the sleeved condition (P = 0.019) and the non-braced condition (P = 0.002). In the second task, the same variable was significantly decreased in the braced condition as compared to the sleeved (P = 0.001) and the unbraced condition (P \u3c 0.001). The sleeved condition also produced significantly decreased tibial rotation with respect to the unbraced condition (P = 0.021). Conclusions Bracing decreased tibial rotation in activities where increased translational and rotational forces were applied. Because knee braces decreased tibial rotation, they can possibly be used with ACL-reconstructed and ACL-deficient patients to prevent such problems. Level of evidence Case–control study, Level III