Forces applied at the footrest during ergometer kayaking among female athletes at different competing levels – a pilot study

In analysis of elite sport performance, ergometers are constructed to reflect the specific sport performance analysed [1]. The ergometers measure the work or power during the test [2] and sometimes also assess specific performance indices such as distance, time and speed. Few ergometers, however, provide information about force development during exercise. In kayaking, air braked kayak ergometers are often used for measurement of power output [1]. Previous testing on kayak ergometers [3] has been shown to reflect the physiological response during flat-water kayaking.

Kayaking engages large muscle groups to drive the kayak as fast as possible through the water. The kayaker has to overcome the drag force, which acts in the opposite direction to movement. Hydrodynamic (boat) and aerodynamic (boat and paddler) drag is generated as the kayak moves through the water [4]. The paddle in the water acts to transmit the net forces developed within the kayak by the paddler to provide forward propulsion. The forces developed at the paddle driving the kayak through the water have been thought to be produced mainly by upper body muscles [5‐7].

There have only been few studies of the forces developed within the kayak during paddling. Aitken and Neal [8] found peak forces of 200 N in sub-elite kayak paddlers to be applied to the paddle during kayaking. In elite kayak paddlers Baker [9] measured peak forces of about 375 N in men and 290 N in women at the paddle. Since force development at the foot stretcher during the driving phase of the stroke has been shown to influence power output in rowing [10], similar conditions may apply to kayaking. Most elite kayakers apply some form of fixation of the feet to the footrests at least during competition. This allows both pushing and pulling forces to be applied to the footrest. We are not aware of any previous studies of the forces at the footrest and seat in kayaking, as also pointed out in a recent review article [4].

The aim of this preliminary study was to determine the forces applied at the footrest during ergometric kayaking in individual kayakers at different competitive levels – junior elite, national elite and international elite.

VO₂ during the all-out test is shown in Fig. 1. All three subjects reached a plateau in VO₂, though not as succinct in the junior kayaker, and respiratory exchange ratio exceeded 1.1 during the all-out test. The results of measurements during exercise are presented in Fig. 2. The subjects are sorted by increasing power during the test. As could be expected, the rank order was the same for power, VO_2peak and competition time, both at 500 and 1000 m (Table 1). The relative differences between the three athletes were similar for power (At All-out 155; 182; 235 W), VO_2peak (at All-out 3.2; 3.3; 3.9 L/minute) and forces at the paddle (At All-out144; 183; 192 N). There were, however, dramatic differences in the forces applied at the footrest (At All-out pull 23; 77; 150 N), where the most accomplished paddler generated forces 3 to 26 times as high as the least accomplished paddler (Table 1).

The main finding of this study was that the kayakers at different competitive levels in this study generate considerably different forces on the footrest during paddling on a kayak ergometer.

Aitken and Neal [8] reported peak forces (right paddle 213.5 ± 9.6 N, left paddle 200.6 ± 7.9 N) measured with strain gauges on the paddle shaft during 500 m on-water kayak paddling in sub-elite kayak paddlers. Baker [9] has reported higher peak forces (men 1000 m 375 N, women 500 m 290 N) during on-water measurements in kayak paddlers from the Australian national team. Our findings are compatible with the previous studies, despite the fact that we had only three female subjects and that the relationship between force measurements on water and in a kayak ergometer is unknown.

We have measured forces at the footrest during kayaking. Forces at the footrest have previously been measured during rowing. Caplan and Gardner [12] thus found that mean power increased with pulling forces of the footrest. Pushing forces at the footrest during rowing have been proposed to relate proportionally to forces at the oar blade [2, 13]. In rowing the oars are attached to the boat [14]. This is mechanically different from kayaking, where there is no attachment between the paddle and the boat. In rowing, the forces from the oars act rather symmetrically on the boat and rower and the boat is pushed forward through the feet. In kayaking, the kayakers themselves have to transfer the force from the paddle to the boat via the body [6]. Since the force in the paddle blade, that drives the kayak forward, acts a distance away from the centre line of the kayak, every stroke will tend to turn the craft. This is partly compensated for in the boat design. The moment may also need to be balanced by sideway forces in the seat being stabilised by a pulling force in the foot at the opposite side from the active side. A high moment from a high power, could then be balanced from pulling force in one foot.

Timing between upper body and lower body seems to be important during ergometric kayaking by looking at the force curves (Fig. 3) from the three athletes. Even further seems the coordination between the pushing and pulling movement also to be important. One could speculate that the timing of the moment is important to be able to produce high power. A paddle stroke involves rotation of the torso from the shoulders to the pelvis [4]. Rotation of the pelvis is likely to involve leg muscles and application of forces on the footrest may help stabilising the torso during the movement.

Earlier it has been suggested that high aerobic and anaerobic capacity are the most important factors distinguish between elite kayakers [5, 7]. Our findings suggest that timing and biomechanical factors as forces at the feet have greater impact on performance (Fig. 2).

Our preliminary results show that while the relative differences in power, VO₂ and forces at the paddle were similar in the three athletes, there were very large differences in forces at the foot rest. Technical aspects of paddling, e.g. stroke profile and the direction of force at the contact between paddle and water may conceivably be related to generation of forces at the foot-rest. There are several limitations of this study. The low number of subjects is certainly one. We could only perform the study in association with routine testing during the competition season, which meant that slightly different protocols and different equipment had to be used. The results would however, be the same if we analysed the forces after two minutes in the kayaker who performed four minutes all-out tests. The equipment for measurement of VO₂ had been validated in the same laboratory (Elite Sports Centre Bosön, Lidingö, Sweden), and we are confident that the two units give comparable results. Further studies of the forces at the footrest during kayaking and their relation to power and competition time are needed to confirm our findings. If such relations exist, specific training of the co-ordination between paddle stroke and forces applied at the footrest may help improving performance. Studies of the relation between power and forces with and without fixation of the feet may provide an insight into the importance of pulling forces at the footrest. Forces at the footrest should also be studied during paddling on water, as this may differ from ergometer paddling. More comprehensive measurements of forces and movements are needed to provide a full picture of the biomechanics of kayaking.

Important indices of elite kayaking seem to be forces applied at the footrest as the kayaker performing at the highest level produced the largest forces. Timing and coordination of forces in the paddle and footrest, seems to be important for high kayaking performance. Suggesting that forces at the footrest could be an important indices to assess during training evaluation.