## 4 Discussion  
This study identified aspects of the rowers' technique that can affect sculling performance and could be directly targeted during training, such as arm and trunk positioning at the catch and finish. Other parameters important for performance, such as the slip angles, are more difficult to control directly. However, by identifying the underlying neuromuscular strategies affecting these parameters and the overall performance, it is possible to provide useful information for targeted training protocols. The first objective was to describe the average neuromuscular activation and kinematics patterns from the trunk and upper body in sculling. The neuromuscular activation pattern resembled the one measured on ergometer [18; 19; 21; 22] and water, albeit with smaller and different sets of muscles [22; 23]. Similarly to what was observed on the ergometer [4], the current study observed the absence of co-contraction in the trunk flexors/extensors. It has been demonstrated that co-contraction in pulling is smaller than in pushing tasks [35], and even if the on-water condition is more unstable than ergometer rowing, there is likely not enough instability to require increased core muscle co-contraction. The observed activity of RA for a brief interval at catch, right before the activations of the trunk extensors, might indicate a strategy to reach as far as possible to increase the stroke length, which might be linked to respiration/intra-abdominal pressure due to the strong forces generated at the catch [36] or might be due to the core stabilization known to occur  
Figure 6: Effect of one standard deviation (1 SD) change in the muscle activations on catch slip angle (**A**) and finish slip angle (**B**). Grey squares indicate no statistical significance (\(p\) value > 0.05), while red and blue squares indicate increase and decrease in performance, respectively, with respect to 1 SD change in muscle activation. BB: biceps brachii; BR: brachioradialis; DA: deltoideus anterior; DP: deltoideus posterior; FCU: flexor carpi ulnaris; TBL: triceps brachii longus; RA: rectus abdominis; EO: external obliquus; IO: internal obliquus; ESL: lumbar erector spinae; EST: thoracic erector spinae; TFL: tensor fascia late; GM: gluteus maximus. in preparation of leg movements [37]. Also, the different activation profiles of lower (IO) and upper (RA, EO) trunk flexors show that these muscles have different purposes within a rowing cycle, with the former group dedicated to slowing down the trunk before the finish, and the latter dedicated to flexing the trunk during recovery and bringing the rower back to the catch position. Such a strategy of activating OI and TFL, with almost no contribution from RA during the recovery phase, indicate of the rowers' technique to keep the upper trunk extended during the recovery. Indeed, based on the statistical analysis, an increased RA activation during recovery seems detrimental to performance, being associated with reduced power, speed, and FSA. The activations of DA and TBL during the beginning of the drive phase underline the desire of the rowers to keep their arms extended, which helps in the force transfer from the lower limbs and trunk to the oar. In this initial phase, in line with [PERSON] et al. [23], the BB has very little activation. However, the statistical analysis showed that a slight increase in BB activation, increasing arm stiffness via co-contraction with TBL, could benefit overall performance by reducing the slip angles. The second objective of the study was to investigate the modifying effects of technical determinants, kinematics, and muscle activations on the rowers' performance. In line with what was reported in the literature and what is usually reported by trainers [2; 3; 28], longer length, larger effective angles, and more negative boat accelerations were significantly associated with better performance while higher slip angles had negative effects. At the same time, no significant effect on performance was found for the asymmetries in slip angles and stroke length.