A new device for measuring forces in the footrest and seat during sprint kayaking

INTRODUCTIONDuring kayak paddling, the paddler develops forces in the shaft, which are transferred through the body to the kayak by the two contact points in the kayak: the seat and the footrest [4]. Forces produced in the lower legs contribute positively to the velocity of the kayak during flatwater kayaking [1,2,3]. Brown et al. (2010) investigated the activation of the major muscles in the legs during a stroke cycle on eight international level paddlers (six men and two women). Findings of the study showed a clear activation of the major muscle groups in the trunk and the legs (latissimus dorsi, rectus abdominus, external oblique, rectus femoris, biceps femoris and gastrocnemius) during the stroke cycle. A study by Lee Chong-hoon et al. (2014) showed that the legs contribute with 6 % of the total force production. Further, has (Nilsson & Rosdahl, 2016) investigated the leg kick during maximal velocity. The maximal velocity dropped with 16 % if the legs where restricted compared to non-restricted. The three studies underlines the importance of the leg kick in the stroke cycle [1,2,4]. There are currently no studies, which has investigated the forces applied on the seat in the kayak. However, as the seat is one of two contact points between the athlete and the kayak, forces must be applied here as well.Michael et al. (2010) compared a regular fixed seat with a swivel seat (a seat that can rotate around the centre axis) on a kayak ergometer. The swivel seat did produce a 6.5 % higher power output. This may underline that the type of seat may have a significant influence on the performance [3].The purpose of this study is to develop a device, which can measure the forces transferred to the footrest and seat during on water kayaking. It is of great importance that the device does not hinder the kayak athletes in their paddling technique.METHODSThree force transducers (LCM200 Miniature Tension and Compression Load Cell, Futek -10 Thomas, Irvine, CA 92618 USA) were used in the devices, two in the footrest and one in the seat. The footrest device consists of a metal plate shaped like a Nelo fourth generation footrest, the footrest can be seen on figure 1. Aluminum spacers are screwed onto the plate, together with two Futek load cell, threaded into the metal plates of the footrest. On top of the spacers are two separated plates screwed onto the spacers, the two plates are respectively on the left and right side of the footrest, making it possible to distinguish left from right on the footrest. Rubber-rings has been added between the screws in order to minimize shear forces and noise. The footrest plate is fixed to the original frame of the footrest, thereby; it can fit into a Nelo 4 kayak. A Nelo seat was used for the seat device. The seat was fixed on a linear ball bearing (T rail TW-01 drylin®), which sided on a steel profile. A Futek load cell was attached to the sliding seat, the load cell was attached to a metal bar, which were fixed to the seat frame of the boat. So in order to set the preferred seat - footrest distance, one must move the metal bar in order to move the seat. A portable custom built data-acquisition system was made. The system consists of a LattePanda microcontroller with windows 10 which where is running MATLAB. A DAQ NI USB-6009 (National Instruments, Austin, Texas) was used an A/D converter, single-ended was used. A biovision force amplifier (Biovision, Wehrheim, Germany) was placed after each transducer. Each force transducer required an excitation voltage of +/- 10 volts. Each force transducer was set to sample rate of 1000 Hz. An Anker power bank (Anker, Seattle, USA) of 20100 mAh which could provide 5 volts and 4.8 A powered the setup. REFERENCES[1] Brown Mathew., Lauder M., Dyson R. (2010). (2010). Activation and contribution of trunk and leg musculature to force production during on-water sprint kayak performance; Paper presented at the XXVIII International Conference on Biomechanics in Sports,[2] Lee Chong-hoon, N. K. (2014). Analysis of the kayak forward stroke according to skill level and knee flexion angle. International Journal of Bio-Science and Bio-Technology, 4(4), 41-48. [3] Michael, J. S., Smith, R., & Rooney, K. (2010). Physiological responses to kayaking with a swivel seat. International Journal of Sports Medicine, 31(8), 555-560. 10.1055/s-0030-1252053[4] Nilsson, J., & Rosdahl, H. (2016). Contribution of leg muscle forces to paddle force and kayak speed during maximal effort flat-water paddling. International Journal of Sports Physiology and Performance, 10.1123/ijspp.2014-0030 Retrieved from http://urn.kb.se/resolve?urn=urn:nbn:se:du-20578