APPLICATION OF ELECTROMYOGRAPHY IN MOVEMENT STUDIES

The scope of this paper is to provide sound principles of EMG signal acquisition and processing in order to optimise the quality of signal and therefore lead to a better interpretation of mechanical muscle output during movement studies. Some background information will be provided on the origin of the EMG signal, factors affecting the quality of signal, recording techniques, signal processing, the fidelity and reproducibility of the signal, and few applications in movement studies. EMG has been a subject of laboratory research for decades. Only with recent technological developments in electronics and computers has surface EMG emerged from the laboratory as a subject of intense research in particularly movement studies, rehabilitation and occupational and sports medicine. Most of the applications of surface EMG are based on its use as a measure of activation timing of muscle, a measure of muscle contraction profile, a measure of muscle strength of contraction (physical load or psychological stress) or as a measure of muscle fatigue

PRESSURE MEASUREMENT BETWEEN A FUNCTIONAL KNEE BRACE AND THE LEG

When functional knee brace is applied on the leg, the kinematics and kinetics of the knee may be changed due to the relative motion of the brace to the leg and by external compression induced by the straps of the knee brace (DeVita, Lassiter, Hortobagyi, & Torry, 1998; Styf, Nakhostine, & Gershuni, 1992). If the brace moves during dynamic movement, the alignment of both centers of rotation of the knee and brace might induce more resistance to the motion. At the same time, the external compression by the strapping of the brace might cause high intramuscular pressure beneath the area of the brace straps. The intramuscular pressure under the strapping decrease local muscle blood flow and muscular oxygenation, and induce premature muscle fatigue. In this situation, functional knee braces do not improve performance and may even inhibit performance in asymptomatic athletes. The purpose of this on-going research was to measure the knee brace migration on the leg and pressure induced on the leg by the brace straps during dynamic motion. This work will only report the results on pressure and force measurements

KNEE AND BOOT 3D KINEMATICS DURING FORWARD ACCELERATION IN ICE HOCKEY SKATING MEASURED WITH A MOBILE CAMERA ARRAY

The purposes of this study were three-fold, the first purpose was to determine the spatial kinematics at both the knee and ankle joint, the second objective aimed at identifying differences in the kinematics of the joints over consecutive push-offs (PO) and the third objective was to verify the adequacy of using a novel method for video-data acquisition for the analysis of ice hockey skating. Statistically significant (ANOVA, =0.05 & Scheffe post-hoc) differences between knee joint Range of motion, angle of maximum and initial knee flexion were found between the first and subsequent PO. Ankle joint data were more similar than knee joint values. This uniformity at the ankle joint could result from hockey skate boots being very stiff. Future research using this approach is warranted and should focus on the effects of skate design on the skating motion as well as include the hip joint into the analysis

THREE-DIMENSIONAL KINEMATICS AND EMG OF THE LOWER LIMB OF MALE AND FEMALE ATHLETES PERFORMING A SINGLE LIMB LANDING

The purpose of this study is to compare the time-frequency characteristic, the amplitude and the timing of recruitment of the EMG signal, as well as the three-dimensional kinematics, of the lower limb of female and male volleyball players performing a onelegged drop jump landing. Results showed that women landed with significantly higher peak knee abduction angles than men. Furthermore, peak activity of the semitendinosus, relative to initial contact (IC), occurred significantly sooner (prior tolC) for the female athletes than the male athletes (following IC). The male volleyball players' timing might be more protective to the ACL as the peak anterior tibio-femoral shear force is generated after IC. In addition, no gender differences were found for median frequency of muscle activity prior to and following IC

THE EFFECT OF FUNCTIONAL KNEE BRACE MIGRATION ON THE KNEE JOINT MOMENT AND POWER PATTERNS DURING WALKING

The purpose of this investigation was to determine the differences in joint moment and power patterns during walking with and without a functional knee brace and when the brace was deliberately misaligned with the knee axis of rotation. Five participants were asked to walk over a force platform with and without the brace as well as during a condition where the axis of rotation of the brace had been deliberately shifted 1 cm down the leg. Inverse dynamics were used to calculate changes in joint moments and powers at the knee joint. Initial findings indicate that the extensor moment during push-off and ils corresponding eccentric power were greatest in the braced and misaligned brace conditions, though the differences in peak joint moments and powers between these two conditions was not large enough to implicate brace migration as an injury mechanism

EMG AND 3D KINEMATICS OF THE LOWER LIMB OF MALE AND FEMALE ELITE SOCCER PLAYERS PERFORMING AN UNANTICIPATED CUTTING TASK

The purpose of this study is to compare the timing of recruitment and the amplitude of the EMG signal, as well as the three-dimensional kinematics, of the lower limb of female and male elite soccer players performing an unanticipated cutting manoeuvre. Results showed that women performed the cutting task with significantly higher knee valgus angles at initial ground contact (IC) and higher peak knee valgus angles than men. Furthermore, onset of the semitendinosus and peak biceps femoris activity occurred significantly sooner for the female athletes than for the male athletes, which may increase strain on the ACL. Women also executed the task with greater RF and BF activity. This increased hamstring activity may be a compensatory mechanism to offset increased knee joint laxity in order to achieve functional joint stability

DIFFERENCES AMONGST BONE, SKIN, AND SKATE MARKER-BASED ROTATIONS OF THE FOOT DURING PUSH-OFF IN SKATING

The present study aims at exploring differences amongst bone, skin, and skate marker based rotations of the foot during skating. A vector that passes through two markers on the bone, a vector that passes through two markers on the skin, and a vector that passes through two markers on the skate were used to represent foot rotations from dorsiflexion to neutral position and from neutral position to plantar flexion based on bone, skin, and skate markers. Paired samples t-tests were used to compare the rotations of different vectors to each other. The results showed that a significant difference amongst bone, skin, and skate rotations existed during plantar flexion but not during dorsiflexion. This significant difference extended to the total motion from dorsiflexion to plantar flexion where skate rotations were 26% smaller than bone rotations and 49% smaller than skin rotations. Bone rotations were 31 % smaller than skin rotations. Based on the results of this study, it can be concluded that, unlike shoe motion, the rigidity of the skate structure causes the skate motion to underestimate the motion of the underlying bony and skin structures

TIME-MOTION ANALYSIS OF ICE-HOCKEY SKILLS DURING GAMES

INTRODUCTION: Time-motion analysis (TMA) has been performed for a variety of sporting activities, including ice-hockey. However, these previous TMA studies of ice-hockey did not differentiate between playing levels and/or playing positions. The main goal of this study is to establish whether differences exist between the skills most frequently performed by players in various positions during actual competition (forwards, defensemen and goaltenders). Furthermore, to determine if there are differences in the skills performed by players of two different playing levels (university and major junior). Recommendations for coaches at the grassroots and elite levels will be made to assist them in more appropriately training players for actual play. METHODS: Ten (5 at each level) regular season games, in the last quarter of the regular season, were recorded on videotape for analysis. This time frame was chosen to ensure that team cohesiveness was well established. One video-camera (total of 6) was assigned to follow a set position on the ice, e.g., one camera for the left wing, right wing, etc. All of the subjects involved in the study gave their informed consent, in accord with the regulations of the Health Sciences Ethics Committee. Analysis of these videotapes was performed by coding the observed skills. Descriptive statistics (mean, std, etc.) on the frequency of occurrence of the specific skills are calculated. RESULTS: Preliminary results show that the most frequently performed skills are skating forward without the puck and gliding forward without the puck. The two skills typically occurred in the neutral zone, even during strength play. Further analysis of the data will point to differences between playing levels and/or positions. Goaltender skills were analyzed separately. These players spend the greatest amount of their time standing in front of the middle of their net. The next most frequent skill for goaltenders, is the ready position, on the left side of the net. DISCUSSION/CONCLUSIONS: At this point of the study, it seems that hockey players spend most of their playing time waiting for the play to develop, and then reacting to what they see happening. This appears to be more easily done by gliding forward on both feet. As well, players spend a very limited amount of their playing time with the puck. Therefore, a significant amount of practice time should be spent in developing the most common skills with a puck, so that players will be more proficient at playing with the puck in game situations. However, skating skills without a puck should be developed equally well, since players rarely have the puck. For goaltenders, it seems that they would benefit greatly from concentration exercises, since most of their time is spent standing in the center of their net. The ready position should also be well practiced, since it is the second most frequent skill for goaltenders

LOWER LIMB KINETICS AND QUADRICEPS ACTIVATION FOLLOWING TOTAL KNEE ARTHROPLASTY WITH THE MEDIAL PIVOT KNEE DURING LEVEL AND INCLINE WALKING

The purpose of this study was to compare gait patterns and quadriceps muscle activity of patients with a Medial Pivot knee to that of healthy, age-matched individuals. Five total knee arthroplasty patients and five age-matched control participants performed a minimum of three walking trials on both level and inclined surfaces, during which lower limb kinetics, kinematics, and muscle activity were recorded. Patients exhibited increased hip and knee extension moments, as well as increased knee flexion and peak power during stance phase of gait, corresponding with increased activation of the vastus medialis. Findings indicate that patients continue to compensate with the non-operative limb at more than 6-months after surgery, while the vastus medialis plays a key role in stabilizing the knee

THREE DIMENSIONAL KINEMATICS AND LOWER LIMB EMG OF ACL DEFICIENT KNEE JOINT WEARING A FUNCTIONAL KNEE BRACE DURING RUNNING

Knee braces have been found to provide limited stability to the ACL deficient (ACLD) knee in situations where the ,knee is loaded during sporting movements. Variability of the gait cycle of the injured knee during strenuous activity with and without a functional knee brace can be expected. Three dimensional (3D) kinematic and electromyography (EMG) data were collected for ten consecutive gait cycles from each participant after running 6 min on a treadmill under both braced and unbraced conditions. Bracing significantly reduced the abduction angle throughout the gait cycle however without reducing the total range of motion (p < 0.05). The functional knee brace showed a consistent trend of setting the ACLD knee in an external rotation position, thus avoiding internal rotation. Our findings supported the mechanical contributions of the brace in limiting abduction and suppressing internal rotation for ACLD knee during strenuous activities