**1. Introduction**

The main goal of competitive swimming is to cover a certain distance in the least possible time. Performance in swimming depends on producing propelling forces and reducing resistance to movement in the water [1]. Maintaining streamlined balance and body position is crucial in enhancing the proficiency of swimmers' performance, which depends on the strength of the core muscles [2]. Several studies recommended adding core strength training to be an integral part of swimming training to improve performance [2–4]. Exercises to train core muscles can be exceptionally beneficial for sprint swimmers, allowing the effective transmission of force between the trunk and the upper and lower extremities to propel the body through the water, which leads to increased athletic performance and improved functional skills [5].

The enhancement of force production resulting from core training is achieved by improving neural adaptation, leading to faster nervous system activation, improved synchronisation of motor units, increased neural recruitment patterns, and lowered neural

**Citation:** Khiyami, A.; Nuhmani, S.; Joseph, R.; Abualait, T.S.; Muaidi, Q. Efficacy of Core Training in Swimming Performance and Neuromuscular Parameters of Young Swimmers: A Randomised Control Trial. *J. Clin. Med.* **2022**, *11*, 3198. https://doi.org/10.3390/ jcm11113198

Academic Editor: David Rodríguez-Sanz

Received: 14 April 2022 Accepted: 2 June 2022 Published: 3 June 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

inhibitory reflexes [3,4]. These elements can be particularly beneficial for sprint swimmers [3]. Moreover, they reduce training costs and effort and help coaches choose the most appropriate training program to assess which swimmers could improve their performance effectively. Furthermore, they can reduce the rate of injuries by improving the efficacy of core muscles [3]. A strong core enables athletes to perform more effectively and conduct swift body movements, enhancing force distribution throughout the body [6]. A weak core leads to energy leakage, resulting in less powerful kicks and a decreased overall amount of power produced [7].

Previous studies focused on the effects of land-based limb power and strength interventions, with inconsistent findings with regard to swimming [8]. Furthermore, there is limited evidence regarding applying core-training programs to swimmers in terms of swimming performance. Weston et al. [9] reported an improvement in front crawl swimming time and core muscle functions following a 12-week isolated core-training program among young swimmers. A recent study by Karpi ´nski et al. [10] also reported an improvement in swimming performance following a six-week core-training program among national-level Polish swimmers. Patil et al. [2] also reported an improvement in sprint time following six weeks of a core-training program in competitive swimmers. At the same time, Martens et al. [11] did not show a direct relationship between improvement in core muscle strength and swimming performance. There is also a lack of accurate performance measurements in core muscle training among swimmers [9,12]. Even though few studies are available that have assessed swimming speed, most of these studies did not assess accurate swimming parameters such as stroke rate, stroke length, sprint time, stroke index, etc., following the core-training program. It is also important to assess the performance parameters of the key core muscles that maintain the body position during swimming, such as the external oblique, erector spinae, and latissimus dorsi.

Tensiomyography (TMG) is a novel and non-invasive neuromuscular measurement used to quantify the contractile properties of the muscles and provide information about how the muscles respond to the exercises and the load [13,14]. It has also been used to assess muscle stiffness and composition [15]. The assessment of the contractile properties of the muscles can provide valuable information about the adaptations of the muscles in response to the training. Several researchers used TMG to measure the effect of various training loads in soccer [16–18], volleyball [19,20], and basketball players [21] and monitor the effects of physical training in soccer and basketball players throughout the season [21,22]. TMG has also been used to establish the relationship between neuromuscular parameters and sports performance indicators in cyclists [23] soccer [24] and rugby players [25]. To the best of the authors' knowledge, TMG has never been used to quantify the effect of core training among swimmers. Therefore, this study aimed to investigate the efficacy of a six-week core-training program in the swimming performance and neuromuscular properties of young swimmers. We hypothesised that an additional core-training program, along with a regular swimming training program, would lead to positive changes in the performance of young swimmers. This is the first study to use TMG to measure the effect of core-training exercises on swimmers.

### **2. Materials and Methods**
