# Antagonist Muscle Co-Activation during Kettlebell Single Arm Swing Exercise
###### Abstract  
The purpose of this study was to determine the muscle activation and co-activation of selected muscles during the kettlebell single arm swing exercise. To the best of our knowledge, this is the first study investigating the muscle co-activation of a kettlebell single arm swing exercise. Nine volunteers participated in the present study (age: 22.6 \(\pm\) 3.8 years; body mass: 80.4 \(\pm\) 9.2 kg; height: 175.6 \(\pm\) 7.5 cm). The electrical muscle activity of eight right agonist/antagonist muscles (AD/PD, ESL/RA, ESI/EO, and GM/RF) were recorded using a surface EMG system (Myon m320 RX; Myon, Switzerland) and processed using the integrated EMG to calculate a co-activation index (CoI) for the ascending and descending phases. A significant effect of the ascending and descending phases on the muscles' CoI was observed. Post hoc analyses showed that the co-activation was significantly higher in the descending phase compared to that in the ascending phase of AD/PD CoI (34.25 \(\pm\) 18.03% and 24.75 \(\pm\) 13.03%, \(p<\) 0.001), ESL/RA CoI (34.97 \(\pm\) 17.86% and 24.19 \(\pm\) 10.32%, \(p<\) 0.001), ESI/EO CoI (41.14 \(\pm\) 10.72% and 30.87 \(\pm\) 11.26%, \(p<\) 0.001), and GM/RF CoI (27.49 \(\pm\) 12.97% and 34.98 \(\pm\) 14.97%, \(p<\) 0.001). In conclusion, the co-activation of the shoulder muscles varies within the kettlebell single arm swing. The highest level of co-activation was observed in the descending phase of AD/PD and GM/RF CoI, and the lowest level of co-activation was observed during the descending phase, ESL/RA and ESI/EO CoI. In addition, the highest level of co-activation was observed in the ascending phase of ESL/RA and ESI/EO CoI, and the lowest level of co-activation was observed during the ascending phase, AD/PD and GM/RF CoI. The co-activation index could be a useful method for the interpretation of the shoulder and core muscles' co-activity during a kettlebell single arm swing. kettlebell; antagonist muscle; electromyography; co-activation; movement analysis; injury prevention; wearable technologies +
Footnote †: journal: Medicaljoint extends via the activation of the gluteus maximus and the hamstrings synergistically. Meanwhile, the shoulder joint flexes to 90\({}^{\circ}\), supported by the activation of the anterior deltoid [4; 5; 6]. In the descending phase, the hip joint flexes via the activation of the gluteus maximus and the hamstrings eccentrically. Meanwhile, the shoulder joint extends, supported by the eccentric activation of anterior deltoid [1]. The coordinated recruitment of core muscles has a key role in trunk stabilization, allowing for an effective transfer of forces from the hip to the arms holding the kettlebell [1; 2; 7]. [PERSON] and [PERSON] [6] suggested that the mechanical demand of a kettlebell swing exercise appears to be sufficient to elicit increases in the ability to apply force quickly. Therefore, the kettlebell swing exercise could prove a useful addition to strength and conditioning practitioners interested in developing their athletes' ability to rapidly apply large forces to sports-specific resistances. To our knowledge, there are only few studies that have investigated muscle activation via surface electromyography in the kettlebell swing exercise. Studies focused on the muscles most involved (such as the rectus abdominis, internal oblique, external oblique, lower and upper erector spinae, gluteus maximus, gluteus medius, biceps femoris, and anterior deltoid). [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [5] showed that both a two-handed and single-handed kettlebell swing provide sufficient muscular recruitment for the strengthening of the gluteus maximus, gluteus medius, and biceps femoris. Single armed swings showed greater activation levels than two-armed swings, with greater activation on the contralateral side of the upper erector spinae and the ipsilateral side of the rectus abdominis [1].