## 4 Discussion  
We determined the best rowing seat cushion pressure and rowing cadence conditions that increased tissue oxygenation and blood volume of the erector spinae muscle, increased cardiopulmonary stimulation, and reduced effort during exercise and recovery periods. The present study confirmed that rowing on cushion pressure under 80 mmHg can increase O2 Hb and tHb during the exercise period, whereas fast rowing can result in a higher HR. Moreover, we also determined that a cushion pressure of 140 mmHg is suitable for slow rowing and can increase O2 Hb and tHb in the recovery period and reduce effort. In the present study, we determined that the tissue oxygenation and blood volume of the erector spinae under different seat cushion pressure levels increased during the exercise period. The increments of O2 Hb and tHb at 80 mmHg were higher than those at 0 mmHg. This may have been caused by a slight increase in the sway of the lower back in the sagittal plane under 80 mmHg pressure, but the sway did not cause instability. However, it increased the flexion-extension activity of the lumbar spine and even reduced the contraction of the erector spinae. In a previous study, which used the same rowing conditions (i.e., same rowing machine, seat cushion, and cadence) as the present study, researchers determined that the seat cushion pressure of 80 mmHg increased sagittal sway in the lower back (about + 4%) during rowing but slightly reduced erector spinae activation (reduced from 10.89% to 10.11% maximum voluntary isometric contraction (MVIC)) compared with stable surface erector spinae activation [28]. Movement of the spine helps improve fluid transport in intervertebral discs and has beneficial effects against shrinkage of the spine and compression of intervertebral discs [24; 25; 26]. However, if isometric contraction intensity is greater than 20% MVIC, tissue oxygen levels and blood volume decrease with increases in contraction time and intensity [31]. Therefore, blood and oxygen reperfusion during the rowing recovery phase (which occurred as the participant returned to the catch position for the next stroke) could be increased by increasing lumbar activity (including muscle contraction and relaxation), but the intensity of muscle contractions should be maintained under low activation. For example, in the present study, rowing on  
Figure 6: Responses of RPE to various pressure and rowing cadence conditions during the recovery period (mean \(\pm\) SE). * Significantly different from low cadence under the same pressure. # Significantly different from 140 mmHg under the same cadence. the seat cushion under 80 mmHg with light resistance increased the tissue oxygenation and blood volume of the erector spinae by slightly increasing potential lumbar activity. However, the tissue oxygenation and of the erector spinae under 140 mmHg were not greater than those under 0 mmHg. The RPE results indicated a significant increase compared with 0 mmHg (\(p\) = 0.083; Table 2). The increased difficulty related to the unstable surface may have caused greater stress, thereby increasing RPE and obstructing tissue oxygenation and blood volume. The previous study also determined that a seat cushion with 140 mmHg of pressure significantly increased lower back sway in the frontal and horizontal planes during rowing but also had a trend intended to increase erector spinae activation (an increase from 10.89% to 12.02% MVC) compared with that under stable surface conditions [28]. Therefore, according to the results of the present study, higher cushion pressure does not always lead to increased muscle oxygenation and blood volume. A proper cushion pressure range is required to increase tissue oxygenation and blood volume in the back muscles. In the present study, the increases in O2 Hb and tHb during fast rowing tended to be lower than those during slow rowing (\(p\) = 0.067). This indicated that faster stroke rates are not conducive to tissue oxygenation and of the erector spinae muscle.