Evaluation of a rotating swim bench as a surrogate for freestyle swimming

Introduction: The swim bench is an isokinetic ergometer designed for competitive swimming training and is used in research as an accessible alternative to in-water data collection. However, limited literature addresses the biomechanical fidelity of the swim bench relative to in-water swimming. The lack of body roll on a conventional fixed swim bench may limit realistic simulation of the freestyle stroke pull. Accordingly, the KayakPro SwimFast swim bench includes a rotating bench setting; yet specific changes to a competitive swimmer’s kinematics and muscle activity on a rotating bench compared to a fixed bench or in-water swimming are unknown.
The purpose of this study was to assess the effect of swim bench setting on freestyle stroke 3D kinematics and muscle activity and evaluate the similarities between the swim bench and pre-existing in-water kinematic data [1]. The rotating bench setting was expected to produce greater shoulder angles and shoulder roll, narrower elbow angles, and less torso flexion than the fixed. Further, the rotating bench setting was expected to generate greater muscle activation of the shoulder prime movers, rotator cuff and scapular stabilizers. In comparison to the in-water data, the stroke length, elbow flexion, total shoulder roll, and length of entry phase were expected to differ on the swim bench.

Methods: Fifteen, male, right-handed, collegiate and national level competitive swimmers [20.4±1.18 yrs., 1.81±5.11 m, 78.5±6.01 kg] recruited from local varsity swim teams participated. Upper limb and torso kinematics were collected bilaterally, and surface electromyography (sEMG) collected on 12, right, upper limb muscles. Participants performed 8 sets (4 rotating & 4 fixed) of 30 seconds freestyle stroke pulling on a KayakPro SwimFast swim bench (KayakPro USA LLC, Florida, USA) at 55 stroke cycles/minute.
Kinematic data was filtered with a low-pass Butterworth filter at a 4 Hz cut off, and time normalized to percent stroke cycle (%SC). sEMG data was filtered with a band-pass Butterworth filter between 30 to 500 Hz, amplitude normalized to maximum voluntary isometric contraction and time normalized to %SC. Swim bench setting continuous joint angles and muscle activations were compared using statistical non-parametric mapping, one-tailed, paired t-tests. In-water measures were compared to the swim bench using mixed one-way ANOVAs via JMP 17 software (SAS Institute, North Carolina, USA).
Results & Discussion: Contrary to the hypotheses, few kinematic and sEMG differences existed between the rotating and fixed swim bench settings. Significant differences were found in the right shoulder elevation (p = 0.021) (Fig. 1), posterior deltoid activation (p = 0.015) (Fig. 2), and infraspinatus activation (p = 0.026). However, the fixed bench produced greater activations and angles rather than the hypothesized rotating setting. Regardless of bench setting, participants laterally flexed the torso, potentially as compensation for the lack of roll allowance on the swim bench overall. The similarities between the settings indicate that the rotating swim bench may not substantially augment the realistic simulation of the underwater freestyle pull. Thus, swimmers can choose the more comfortable setting for training.
Compared to in-water swimming, both swim bench settings produced similar elbow flexion ranges; however, the stroke length decreased (p<0.0001), total shoulder roll decreased (p<0.0001), and entry phase duration decreased (p<0.0001) significantly. Despite the difference in shoulder roll magnitude, the movement pattern aligns with current literature, indicating at least partial replication of in-water swimming [2]. The reduction in stroke length may relate to the lack of entry phase on the swim bench because swimmer’s commonly glide further forward during entry and elevate the shoulder to facilitate a longer moment arm for the catch [3]. The reduction in stroke length, total shoulder roll, and entry phase duration with the addition of the lateral torso flexion are notable considerations for long term use. Swimmers could develop associated habits that reduce swimming economy and increase drag when translated to in-water training.
Significance: This study provides novel findings for coaches and researchers to consider for the use of the swim bench for training and research purposes.