## 1 Introduction  
Exercises for strengthening core muscles are currently being widely promoted. These exercises have been used as a part of prevention and rehabilitation programs for musculoskeletal injuries [1, 2]. However, limited and conflicting evidence exists regarding their efficiency for the improvement of sporting performance. This is most likely due to the lack of sport-specific tests evaluating the stability and strength of core muscles. Sport training induces specific adaptations of the core, which may not be revealed using non-specific tests [3]. In practice, the biomechanical analysis of techniques, the experience of strength and conditioning specialists and their training evidence have been generally used. Another drawback is that most of the tests do not target the spine-stabilizing muscles despite the fact that the most important stabilizers are task specific [4]. Selecting an appropriate test to assess core muscle stability and strength is difficult because of the interaction of the lumbopelvic hip structures. Core stability in static single-joint and dynamic multi-joint exercises may not correlate due to its high level of task specificity [5]. Static core muscle stability and strength tests may therefore be unable to distinguish between power-trained athletes and assess the effect of training involving dynamic core muscle exercises. This low sensitivity of current testing methods limits their practical applications. Tests used to assess active trunk control during functional tasks are restricted to linear movements that lack the explosive movements associated with sporting activities [6]. In practice, a medicine ball or cable pulleys can be used for this purpose, as they allow motion in all three planes. For instance, one can use a device that allows the monitoring of biomechanical variables during trunk rotations in the form of a modified woodchop exercise while sitting [7] or standing [8]. The protocol including a diagonal chop and lift power exercise generates reliable data and it seems to simulate dynamic movement of the trunk [6]. Although rotational power is a fundamental component in functional tasks, such as striking or throwing, [PERSON] et al. [9] suggest that rotational power measured during the chop and lift may not be an essential factor in throwing velocity in cricket. The external validity of isometric and isokinetic strength tests of the trunk muscles for functional tasks is also ambiguous. Some authors have documented the relationship between measures of core muscle strength and athlete performance [10; 11], whereas others have not [12; 13; 14]. The relationship between the limbs and core muscles has been demonstrated for various lifting tasks, forehand and backhand strokes in tennis, overhead throwing in baseball and so forth [15; 16; 17; 18; 19; 20; 21]. These findings highlight the importance of core musculature in the transfer of momentum and torque throughout the kinetic chain during sport-specific tasks [4]. Furthermore, there are no significant differences in peak torque measured using an isokinetic dynamometer between and within groups of highly skilled golfers and healthy individuals who do not play golf [22]. Further, no significant differences were found in the trunk muscle endurance between the elite golfers and the controls [22]. Similarly, no significant differences in the static holding times and a decline in the electromyography (EMG) median frequency between low-handicap golfers with low back pain and healthy non-golfing controls were reported [23]. The shortcomings of these laboratory tests is that strength characteristics of core muscles are measured when sitting in a fixed position. However, core muscles facilitate trunk movements more easily when the body is in an upright position [24], thus between- and within-group differences in strength and power produced during trunk rotations can be better revealed. Therefore, to be relevant to a particular sport, core muscle stability and strength tests must mimic their specific movements very closely.