Characteristics of the Shrug Motion and Trapezius Muscle Activity During the Power Clean.

ABSTRACT: Nagao, H and Ishii, Y. Characteristics of the shrug motion and trapezius muscle activity during the power clean. J Strength Cond Res 35(12): 3288-3295, 2021-Although the shrug motion and trapezius muscle activity are commonly considered as important in Olympic weightlifting exercises, there are no data on the shrug motion in Olympic weightlifting. Providing objective data on shrug motion and upper trapezius muscle (TZ) activity during power clean (PC) will help coaches properly evaluate technique and select accessory exercises. The purpose of this study was to clarify the role of the shrug motion and TZ activity during PC. Twenty trained men performed the PC at 50, 70, and 90% of 1 repetition maximum (1RM). Kinematics motion data and TZ surface electromyography were recorded. The range of motion of the shrug angle (sROM) and scapular adduction angle (aROM) were calculated during each phase of the PC. The TZ activity of each phase was evaluated by the root-mean-square of TZ activity (TZ%RMS), normalized by the maximal voluntary contraction. In the first pull and transition phases, TZ%RMS was significantly larger (p < 0.05; η2 = 0.10, 0.11) at 90% 1RM than at 50% 1RM. In the second pull phase, the sROM and aROM were significantly larger (p < 0.01; η2 = 0.19, 0.19) at 50% 1RM than at 90% 1RM, and the TZ%RMS was significantly larger (p < 0.01; η2 = 0.30) at 50% 1RM than at 70% 1RM and 90% 1RM, and at 70% 1RM than at 90% 1RM. Trapezius muscle activity appears to work to maintain scapular position, especially in the first pull and transition phases. In the second pull phase, the TZ was aggressively contracted to elevate the scapula and pull the barbell, but the sROM decreased as the load increased.

Why does the Quiet Eye improve aiming accuracy? Testing a motor preparation hypothesis with brain potential.

The purpose of the present study was to determine whether the Quiet Eye (QE) acquired over time is associated with motor preparation processes by using movement-related cortical potentials (MRCPs). Eighteen male, right-handed college students voluntarily participated in this study. Participants performed a dart throw while wearing an eye-tracking system and electrode cap to measure electroencephalogram waveforms (EEG). After performing the dart task, participants were randomly assigned to a Quiet Eye training group (QET) or control training group (CT). Six subjects were excluded due to incomplete electroencephalography (EEG) data. MRCPs were analysed separately within 4 QE categories: High performance score and Long fixation time (HL), High performance score and Short fixation time (HS), Low performance score and Long fixation time (LL), and Low performance score and Short fixation time (LS). Results revealed that although the QET group acquired QE characteristics, MRCPs did not differ between the two groups. Thus, a longer-term experimental design may be necessary to observe EEG changes. Furthermore, QE durations may relate to not only motor programming but also online control.

The inhibition of motor contagion induced by action observation.

In sports, success and failure are believed to be contagious. Yet it is unclear what might cause contagion. This study investigated whether motor contagion is associated with the active observation of the kinematic actions of others. In Experiment 1, six skilled hammer throwers threw a hammer after watching a video of a model throwing toward the left, center, or right. The video included two types of action kinematics which resulted in throw directions that were either easy or difficult to predict based on the model's kinematics. In Experiment 2, the athletes threw hammers after watching the same stimuli as Experiment 1, but while engaging in one of two types of focus (self-focus or non-self-focus) to determine whether motor contagion could be diminished. Results demonstrated that the direction of each participant's throw was more influenced by the videos that contained easy action kinematics, supporting a critical role for the meaningfulness of the link between an action and its outcome in producing motor contagion. Motion analysis revealed that motor contagion was not likely to be a result of the observer imitating the model's action kinematics. The contagion observed in Experiment 1 disappeared when participants engaged in self-focus. These results suggest that motor contagion is influenced by the predictability of an action outcome when observing an action, and that motor contagion can be inhibited through self-focus when observing.

Warm-up with weighted bat and adjustment of upper limb muscle activity in bat swinging under movement correction conditions.

The effects of weighted bat warm-up on adjustment of upper limb muscle activity were investigated during baseball bat swinging under dynamic conditions that require a spatial and temporal adjustment of the swinging to hit a moving target. Seven male college baseball players participated in this study. Using a batting simulator, the task was to swing the standard bat coincident with the arrival timing and position of a moving target after three warm-up swings using a standard or weighted bat. There was no significant effect of weighted bat warm-up on muscle activity before impact associated with temporal or spatial movement corrections. However, lower inhibition of the extensor carpi ulnaris muscle activity was observed in a velocity-changed condition in the weighted bat warm-up, as compared to a standard bat warm-up. It is suggested that weighted bat warm-up decreases the adjustment ability associated with inhibition of muscle activation under movement correction conditions.

Muscle activation characteristics of the front leg during baseball swings with timing correction for sudden velocity decrease.

This study aimed to clarify the activation characteristics of the vastus lateralis muscle in the front leg during timing correction for a sudden decrease in the velocity of a target during baseball swings. Eleven male collegiate baseball players performed coincident timing tasks that comprised constant velocity of 8 m/s (unchanged) and a sudden decrease in velocity from 8 to 4 m/s (decreased velocity). Electromyography (EMG) revealed that the muscle activation was typically monophasic when responding unchanged conditions. The type of muscle activation during swings in response to decreased velocity condition was both monophasic and biphasic. When biphasic activation appeared in response to decreased velocity, the impact time and the time to peak EMG amplitude were significantly prolonged and the timing error was significantly smaller than that of monophasic activation. However, the EMG onset from the target start was consistent both monophasic and biphasic activation in response to conditions of decreased velocity. In addition, batters with small timing errors in response to decreased velocity were more likely to generate biphasic EMG activation. These findings indicated that timing correction for a sudden decrease in the velocity of an oncoming target is achieved by modifying the muscle activation characteristics of the vastus lateralis muscle of front leg from monophasic to biphasic to delay reaching peak muscle activation and thus prolong impact time. Therefore, the present findings suggests that the extent of timing errors in response to decreased velocity is influenced by the ability to correct muscle activation after its initiation rather than by delaying the initiation timing of muscle activation during baseball swings.

Kinesthetic aftereffects induced by a weighted tool on movement correction in baseball batting.

We investigated the kinesthetic aftereffects of a weighted tool on interceptive performance. Eight college baseball players performed three warm-ups before the interceptive task: a normal warm-up, a recalibrated warm-up with a standard 850-g bat and a 1200-g weighted bat, and a weighted warm-up with a 1200-g bat. For the interceptive task, subjects were asked to swing the standard bat coincident with the arrival and position of a moving target. After the warm-ups with the weighted bat, participants felt that the bat was lighter and swung faster. When participants needed to correct their swings to the target's velocity change, larger timing errors were produced in the weighted than in the normal practice condition. These results indicate that warm-ups with a weighted tool create adverse effects for the movement (re)programming processes in interceptive action. This suggests that warm-ups with a weighted tool for an interceptive task affect the central nervous system and not the peripheral system.

Influence of practice with within-trials and inter-trials changes of target velocity in improving movement correction.

In the present study, the influences of two practice methods on movement correction during interceptive action was examined. Fourteen men practiced intercepting a moving virtual target. One group practiced on a target that changed velocity from 4 to 8 m/sec. during the trial (within-trials change group). The other group practiced under Slow and Fast conditions, in which the initial velocity (4 or 8 m/sec.) remained constant (inter-trials change group). After the practice, both groups showed similar decreases in temporal errors in interception of an acceleration target. However, the within-trials change group showed non-corrected movements, whereas the inter-trials change group showed corrective movements. Thus, the practice methods for within-trials and inter-trials change resulted in different corrective strategies to acceleration target.