# The Effects of a Simulated Duathlon on Trunk Motion: A Sensor Based Approach
## 1 Introduction  
A duathlon is a multisport event that consists of running and cycling followed by another bout of running that is performed sequentially with no recovery between each discipline. Investigating the compounding impacts of multisport events on athletic performance involves complex experimental designs with transitions from one modality to another. In this regard, duathlon shares similarities with triathlon, but with the swimming leg swapped for an additional running section. Akin to triathlon, the amplifying effect of one activity loaded before another remains a prevalent area of exploration [1; 2]. A common configuration in duathlon is the sprint distance duathlon that consists of a 5 km run, then a 20 km cycle, followed by a 2.5 km run [3]. Duathlon is internationally governed by Word Triathlon (WT), formerly the International Triathlon Union (ITU), which consents to global duathlon competitive events. Like triathlon, the most limiting (detrimental) performance effect commonly occurs once an athlete has dismounted the bicycle to commence the final running segment [4]. Nevertheless, while duathletes are known to experiencesimilar performance detriments when running after cycling, there is an absence of research that has examined this phenomenon in the field, that is, in the athlete's natural and familiar environment. The trunk muscles are involved in both running and cycling. The trunk protects the spinal cord and supports the weight of the trunk, transferring it to the pelvis and lower limbs. Here, the trunk and its theoretical centre of mass (CoM) function as part of a cohesive kinetic chain as athletes grapple with the difficulties of switching between different yet equally demanding (e.g., from running to cycling, and then running). While some researchers remain active in the exploration of trunk kinematics in triathlon [5; 6; 7], somewhat surprisingly, given the importance of trunk stability and trunk control in both running and cycling, a scarcity of research exists when duathlon is considered. A study by [PERSON] et al. [8] noted that cycling appears to have an adverse effect on subsequent running performance. The literature is replete with examples of how cycling modifies both kinematics and kinetics of running immediately after cycling. These modifications, specifically detrimental performance decrements, include alterations in neuromuscular [9], physiological [10], and biomechanical [11; 12] parameters of running immediately followed by cycling with significant changes to athlete ground reaction forces detected when running after cycling [13]. Some researchers have found a decrease in stride length and step cadence [4]. The kinematic and kinetic modifications that have been conveyed in running post-cycling are realistic, given the onset of neuromuscular fatigue that occurs during cycling and prior to running. Because of likely alterations to neuronal and neuromuscular firing patterns in athletes running after cycling, a period of adaptation to running is needed. This adaptation of the motor program means that a delay occurs before the instantaneous switch to running [14]. In this instance, a high-intensity run may cause substantial muscle fatigue [15], which could affect subsequent cycling and running performances to a greater extent when compared with triathlon. Established biomechanical methods, such as the evaluation of step-characteristics [16] or lower limb range of motion [17], often lack the capability to quantitatively discriminate between subtle running differences. Consequently, such approaches run the risk of discounting fundamental gait-related information [18]. To that end, various biomechanical measures have been adapted to develop and enhance methodologies. Here, running economy, which is commonly considered as a measure of optimal running performance, is subjective to different interpretations.