## 1 Introduction  
Exercise is commonly performed for work, enjoyment, or health, with the benefits of exercise being well documented [1]. Both sport and everyday activities require a balance of both muscular strength and endurance for success and optimal performance [2]. Generally, the two most common modes of exercise for optimising and maintaining performance are endurance training (ET) and resistance training (RT). ET stimulates both the aerobic and anaerobic energy systems [3], with a subcategory of ET referred to as high-intensity interval training (HIIT), characterised by short, high-intensity bouts of exercise with brief rest periods [4]. Alternatively, RT is most commonly performed to achieve gains in muscular power, strength, and hypertrophy [3]. Exercise professionals have sought to improve the training time efficiency by combining RT with ET, with the combination being referred to as CT [5].  
There are conflicting opinions regarding whether concurrent training is beneficial, with studies reporting a synergistic enhancement in aerobic and strength outcome measures [2; 5; 6; 7; 8], whilst others have observed an interference, where concurrent training results in an observed gain in either aerobic or strength outcomes whilst attenuating the adaptation of the other [9; 10; 11]. When developing an exercise training program, the mode, intensity, and volume of training need to be considered to mitigate or reduce any adaptation interference effects [2; 4]. Importantly, concurrent training can increase the maximal oxygen uptake (VO\({}_{2}\)max) [5; 8; 12], following both high and low intensities of endurance training [12].  
Initially, [PERSON] [13] reported that high-intensity interval training is a superior approach regarding time efficiency for stimulating muscle aerobic metabolic adaptations, with the results being comparable to prolonged (90-120 min) endurance training in two weeks. For CT, [PERSON], [PERSON], et al. [14] reported that CT performed twice weekly over 11 weeks resulted in a similar neuromuscular adaptation to that from RT alone in healthy young women, regardless of the intensity or type of aerobic training [8]. These findings suggest that HIIT combined with RT is a time-efficient protocol for optimising both strength and endurance parameters. Furthermore, [PERSON], [PERSON], et al. [6] observed improvements in a range of physical fitness and health parameters in just two weeks of CT consisting of very short \"all-out\" efforts for both ET and RT.  
A limitation of concurrent training protocols is the prescription of inefficient intersection recovery periods between exercise modes [9; 10]. Critically, there is an abundance of suboptimal RT exercise prescriptions, some of which are not specific to outcome measures, whilst other studies prescribe a single RT exercise [8; 12]. Little is known regarding the effects of a concurrent training program that incorporates high RT loads with full-body movements combined with high ET intensities on the physical performance of young adults [15].  
Thus, we examined the effects of a four-week concurrent training program, combining resistance training using full-body dynamic compound movements and endurance training using an HIIT protocol, in an exploratory observational study. We hypothesised that a concurrent training intervention, when ordered with resistance training first, would increase both strength and endurance performance parameters in four weeks synergistically.