Doma, Kenji, and Deakin, Glen (2009) EMG, force and kinematics between concentric and eccentric contractions of a chin up exercise. In: Proceedings of the 7th Ausralasian Biomechanics Conference. From: ABC7: 7th Australasian Biomechanics Conference, 30 November - 1 December 2009, Gold Coast, QLD, Australia.

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Abstract

NTRODUCTION: The movements during isointertial resistance exercises are typically executed with concentric and eccentric contractions to perform the movement pattern of the exercise (1). Numerous studies have shown a higher electromyography (EMG) response during concentric compared to eccentric contractions (2, 3 and 4). However, the exercises incorporated in these studies have been limited to single-joint movements, and subsequently, only one muscle group at a time has been examined. In addition, the magnitude of force production and the displacement of body segments have yet to be compared between concentric and eccentric contractions of multi-joint exercises in literature.

Consequently, the purpose of this study was to compare the level of muscle activity (MA) between concentric and eccentric phases of a multi-joint exercise, such as a chin-up (CH), and to determine whether tensile force production (TFP) and the kinematics of the exercise would affect the characteristics of MA.

METHODS: Eleven resistance trained males (age 25.5 ± 7.5 years, height 1.78 ± 0.76 m, weight 81.7 ± 11.4 kg) performed five sub-maximal repetitions of CH. The middle three repetitions were examined to compare the average level of MA, TFP and displacement between the concentric and eccentric phases. Maximal voluntary contractions were conducted to normalize root-mean squared electromyography values (NrmsEMG) of the pectoralis major, latissimus dorsi, biceps brachii, triceps brachii, rectus abdominus and erector spinae. The angular displacement of the back and the horizontal displacement of the shoulder and seventh cervical vertebrae (C7) were obtained via kinematic analysis. The TFP was obtained by attaching a load cell (force transducer) between the support and a custom built chin up bar. The NrmsEMG, kinematic and TFP values were analysed using a repeated measures ANOVA.

RESULTS AND DISCUSSION: The NrmsEMG of pectoralis major, biceps brachii, triceps brachii, erector spinae and latissimus dorsi, the TFP and the horizontal displacement of the shoulder and C7 were significantly greater during the concentric compared to the eccentric phase for the CH (p < 0.05). There were no significant differences in NrmsEMG of rectus abdominus and angular displacement of the back between the concentric and eccentric phases for the CH (p > 0.05).

The NrmsEMG of the majority of the selected muscle groups and the TFP during concentric was significantly greater than the eccentric phase. These similar patterns of change for TFP and NrmsEMG between the two types of contraction suggest that the magnitude of load is related to the level of muscle activity (5), supporting the linear EMG-force relationship (6). The greater level of MA during the concentric phase may be due to the muscle fibres producing greater force with eccentric contractions (7), and subsequently, the level of MA during the eccentric does not have to match that of the concentric phase to produce the same magnitude of force. In addition, the overcoming of inertia during the lifting phase, a factor which is absent during the lowering phase, may explain the greater TFP and MA during the concentric compared to the eccentric phase.

The displacement of the shoulder and C7 in the sagittal plane was greater during the concentric compared to the eccentric phase. These kinematic differences are expected since CH is an open-kinetic chain exercise, where the lower extremity is free to move in any cardinal plane. Subsequently, as greater movement occurred during the concentric phase, the level of MA of the selected muscle groups may have been higher in order to stabilize the body. The subjects may have also pulled against the chin-up bar with greater force in order to stabilize the body, producing greater TFP during the concentric phase.

CONCLUSION: The results indicated that the level of MA is greater during the concentric compared to the eccentric phases of the CH for the majority of the selected muscle groups. These differences appear to be due to the alteration in TFP as well as differences in the displacement of the body segment movements between the concentric and eccentric phases.

Item ID:	39405
Item Type:	Conference Item (Abstract / Summary)
ISBN:	978-0-646-52474-0
Related URLs:	https://www.anzsb.asn.au/
Date Deposited:	22 Jul 2019 00:30
FoR Codes:	11 MEDICAL AND HEALTH SCIENCES > 1106 Human Movement and Sports Science > 110699 Human Movement and Sports Science not elsewhere classified @ 100%
SEO Codes:	92 HEALTH > 9299 Other Health > 929999 Health not elsewhere classified @ 100%
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