Differences in trunk and lower extremity muscle activity during squat exercises with and without hammer swing



Twelve healthy men, ages 19 to 45, participated in this study. All participants were physically active and engaged in at least three practices per week. Before the start of the experiment, all participants who had suffered serious injuries in the last 3 months or pain on the day of the examination were eliminated. Participants had to stop when they felt pain during any phase of the test. None of the participants was interrupted due to injury or discomfort during the examination. This laboratory study used a within-participant repeated measures design. Muscle activity was the dependent variable and exercise form was the independent variable. The study was approved by the Tokyo Medical and Dental University Research Ethics Board (research protocol ID number: M2018-162) and followed the principles of the Declaration of Helsinki ( 52nd General Assembly of the World Medical Association, Edinburgh, Scotland, October 2000) for medical purposes. research involving human subjects. All participants provided written informed consent to participate in the study.


This study measured electromyography (EMG) levels in the lower limb and trunk during two exercises. The dominant leg, defined as the leg kicking the ball, was used as the measuring leg. The exercise tasks were the HSS and the CIS (Fig. 1). During exercise, EMG levels of Abd H, TA, TP, PL, rectus femoris (RF), biceps femoris long head (BFLH), semitendinosus (ST), gluteus maximus (GM), Mul and internal oblique muscles (IO) were measured by surface EMG. All exercises were verbally explained and measurements were taken after sufficient practice to familiarize subjects with the test. All measurements were taken on the same day. Four members of the research team collected the data and uploaded it to a digital platform.

Figure 1

Explanation of the Hammerobics synchronized squat and the conventional isometric squat. (a) Hammerobics hammer configuration. (b) Squat synchronized with Hammerobics. (vs) Conventional isometric squat.

Data collection and reduction

Equipment set up

EMG signals were recorded during the exercise task using surface EMG (Ultium EMG, EM-U810M8, Tele Myo2400, Noraxon USA Inc., Scottsdale, AZ, USA) and recorded at 2000 Hz with filtering bandpass (10–500 Hz) on a personal computer (EM-P5, Noraxon) using a receiver (EM-U880, Noraxon). The EMG system and the Noraxon Myvideo system using a NiNOX 125 were synchronized. Before attaching the electrodes, the skin was shaved, abraded and cleaned with alcohol. The application site of electrodes for EMG has been determined according to previous studies17,18,19 and guidelines of SENIAM (URL: http://www.seniam.org/). Surface electrodes (Ambu, Blue Sensor M-00-S, Ballerup, Denmark) were attached 35 mm apart to the Abd H, TA, TP, PL, RF, BFLH, ST, GM, Mul and IO on the right side (Figure 2). The electrodes of each muscle were attached parallel to the muscle fibres. Skin impedance was confirmed to be 20.

Figure 2
Figure 2

The site of application of electrodes for electromyography. (a) medial view of the lower leg, (b) anterolateral view of the lower leg, (vs) anterior view of upper leg, (D) posterior view of upper leg, (e) anterior view of the abdomen, (F) posterior view of the lower back. A: Tibialis posterior, B: Abductor hallucis, C: Peroneus longus, D: Tibialis anterior, E: Rectus femoris, F: Semitendinosus, G: Biceps femoris long head, H: Internal oblique, I: Multifidus, J: Gluteus maximus.

Exercise setup

For the configuration, in HSS, a 7.26 kg (φ: 116.5 mm; NISHI Athletics Goods Co. Ltd., Tokyo, Japan) hammer was attached to each end of the Olympic lifting bar by looping the wire of the hammer. The total length of the equipment from the bottom of the bale to the wire was 0.5 m. The weight configuration is described in Table 1. The weight of the equipment was set according to the participant’s body weight range. In CIS, the total weight of the barbell and the Olympic barbell was adjusted to equal the weight of each participant’s HSS. Participants were instructed to perform HSS and CIS exercises under the same conditions. Prior to starting the task, participants had the chance to experience HSS and CIS exercises for 5-10 min to familiarize themselves to ensure that the body would be kept at the same height and the knee at 90° between exercises. In addition, posture was always assessed visually by the examiner (90° knee angle and systematically using a goniometer). Each type of exercise was performed in two trials.

Martelobic Synchronized Squat

The Hammerobics Synchronized Squat (HSS) is a type of isometric squat exercise in which both hammers are swung simultaneously in the same direction. This exercise creates anteroposterior and vertical movements by swinging hammers that are suspended with wires from each end of an Olympic barbell (Fig. 1). During execution, the amplitude of the oscillating hammers was kept within 90° of the vertical plane for safety reasons14. To perform the HSS, it is necessary to maintain an isometric squat position with an upright upper body posture while moving the hammerheads steadily in the anteroposterior direction. It should be noted that the objective of the exercise is not to see what amplitude can be applied to the hammer swing, but to maintain the amplitude of the swing without disturbing the rhythm of the hammers, using a minimum of body movement , change of posture and rhythm. During the HSS test, ten oscillations were recorded. The movements of the hammer during the HSS test were captured by a high-speed camera synchronized with an EMG system.

Conventional isometric squat

The conventional isometric squat (CIS) is an isometric exercise using a barbell with the same weight as the HSS, in which the individual remains in a squat position to keep the hip and knee angles relatively flexed. Data was recorded for 10 s during the CIS test. For the HSS trial data, three data swings were extracted from the obtained data and used for analysis. The motion during the HSS test was divided into two phases based on the motion of the hammer captured by the high-speed camera. We defined hammer motion with HSS as front to back (FB) and back to front (BF). During the FB phase, the hammer moved from the front of the participants after reaching the highest point, then backwards to the highest point. For the BF, the movement of the hammer is the reverse of that of the FB phase, from the back at the top to the front at the top. EMG levels in each phase were used for analysis. In each CIS trial, we recorded 10 s when the participant was in the initial squat posture. Between data 4.01 to 7.00 s were used.

All raw EMG signals were rectified and smoothed using a root mean square algorithm with a 50 ms time reference. This experimental test was not used for comparison of muscle activity levels between muscles. A comparison of the amplitude of the signals of a given muscle was carried out between the two exercise tasks in an individual in the same session, strictly under the same experimental conditions, and without altering the EMG electrodes.21.22. The mean value used for analysis (μV-s) was calculated and averaged over the three full oscillations during the exercise task, and the mean values ​​were used for analysis23.

Data analysis

Data analysis was performed using IBM SPSS Statistics version 25.0 (IBM Corp., Armonk, NY, USA). The Shapiro-Wilk test was performed to confirm normality. Depending on the normality of the distribution, a one-way analysis of variance or the Kruskal-Wallis test was used to examine the difference between the exercise tasks. The post hoc test for one-way analysis of variance or Kruskal-Wallis test was Bonferroni’s correction. A pa value

Source link


About Author

Comments are closed.