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In this episode, we bring J.T. Hartman on the show to discuss his advanced biomechanics research on the “Differences in Core Rotation and Maximum Forward Reach between Whitewater Kayakers using Feathered and Unfeathered Paddle Blades”. See the results of the study below! As well we have American Meteorological Society Award winner and very special guest, Dr. J. Tom Farrar, on to discuss the effects of man-made climate change on whitewater kayaking. Finally, we cover listener mail and of course rants and raves! As always thank you for listening.
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Differences in Core Rotation and Maximum Forward Reach between Whitewater Kayakers using Feathered and Unfeathered Paddle Blades
by: Elizabeth Prewitt, Jamie Lange, and J.T. Hartman
EXSC 436: Advanced Biomechanics
11 December, 2018
Introduction: The growth in popularity of whitewater kayaking has warranted an expansion of scientific research surrounding the sport. To date, much of the research pertaining to the sport has been centered around Olympic-style flatwater sprint kayaking. Significant research has been done on kayaking-specific kinetic variables, but very little has looked at kinematic variables of kayakers themselves. Whitewater paddlers often utilize feathered paddle blades as a way to maximize power output resulting from increasing core rotation and forward reach.
Purpose: The purpose of the present study was to determine the differences in trunk range of motion and maximum forward reach between kayakers using feathered and unfeathered paddle blades. Hypothesis: The researchers in this study hypothesized that there would be no difference in trunk range of motion or maximum forward reach between kayakers using feathered and unfeathered paddle blades.
Methods: Six active participants from the University of Puget Sound Kayak Club with at least one year of kayak experience volunteered to participate in this study. Subjects came into the lab on two separate occasions consisting of a familiarization trial and experimental trial. In the experimental trial, participants paddled for multiple stroke cycles while being recorded from the transverse plane, using both paddle conditions. Statistical analysis including descriptive means and inferential statistics (t-tests) were performed.
Results: After a paired-samples t-test, a significant difference was found between core rotation and reach, when performed in different paddle conditions — feathered and unfeathered (p < 0.05).
Conclusion: The researchers conclude that the use of unfeathered paddle blades leads to improved trunk ROM and maximum forward reach when compared to the use of feathered paddle blades in whitewater kayakers.
Keywords: whitewater kayaking, core rotation, reach, feathered and unfeathered paddle
Whitewater kayaking is gaining popularity in the realm of extreme outdoor-based sports. Participation in the sport includes outdoor enthusiasts, professional athletes, and even active military personnel and veterans. Since 2004, nine military-affiliated medical centers have adopted some form of kayaking into their rehabilitation programs with an additional nine Veterans Affairs centers expressing interest as well (5). The biomechanical study of whitewater kayakers is a starkly undeveloped area of research. The vast majority of current research pertaining to kayaking has been done on Olympic flatwater sprint kayakers, with much of the data coming from a few sporadic studies performed since the 1980’s (7). Much of this research has looked to improve the power output of kayakers by altering paddle blade shape and stroke technique (4). It is generally agreed upon that kayaking in all forms utilizes power produced largely from transverse rotation of the trunk and upper body, leading to multi-segmental movements which have been shown to improve range of motion in physical therapy patients (3, 6, 2). When looking at kayaking performance, then, it is reasonable to conclude that a person’s ability to rotate their core will positively correlate to overall power production during a stroke cycle (for the purposes of the present study, a stroke cycle was defined as the time from the beginning of a right-hand paddle stroke to the beginning of the next right-hand paddle stroke). As a result of increased core rotation, there is also the possibility of increased forward reach during each stroke cycle. Increased forward reach leads to a lengthening of the power phase of each stroke, ultimately resulting in greater potential for power production during each stroke (2). It has been suggested that maintaining a neutral body position is crucial to the stroke efficiency of kayakers (3). This notion has been suggested as an important factor in stroke efficiency for both male and female kayakers as paddling-specific kinematic differences between them are negligible (1). Increasing the engagement of core rotator muscles has also been linked to increases in trunk stability and performance as well as decreases in rate of injury among kayakers (3).
Real world (on-water) biomechanical analyses of whitewater kayakers are extremely difficult to conduct as a result of harsh conditions, exposure of expensive video analysis equipment to water, and obstruction of anatomical landmarks by necessary safety equipment. As a result, many studies have performed these analyses with the use of kayak ergometers. The use of kayak ergometers in biomechanical analyses has been justified by research which shows that differences in physiological and biomechanical processes between ergometer use and on-water paddling are negligible (8).
Much of the current research evaluating the biomechanics of kayakers has sought to identify the most beneficial magnitude of various kinetic variables, not necessarily the kinematic variables that lead to them. As a result, extremely little research has been done on how the use of feathered (offset) and unfeathered (no offset) paddle blades affects the performance of whitewater kayakers. The researchers therefore believe the present study to be the first to look at how paddle blade offset affects trunk range of motion (ROM) and maximum forward reach. The use of a feathered blade (assuming right-hand dominance) requires a kayaker to hyperextend their right wrist, leading to variance in their ability to fully extend their elbow, flex their shoulder, and rotate their core when compared to use of an unfeathered blade. Hence, the purpose of the present study was to evaluate total trunk ROM and maximum forward reach of whitewater kayakers using feathered and unfeathered paddle blades in a lab setting. The researchers hypothesized that there would be no significant difference in trunk ROM or maximum forward reach between subjects using feathered and unfeathered paddle blades.
Subjects: In this study, a total of six active participants, three male and three female, were recruited via voluntary sampling from the University of Puget Sound Kayak Club. All subjects reported whitewater kayaking one to three times a week and had at least one year of kayaking experience at the collegiate level. The physical characteristics of the participants can be found in Table 1. All subjects completed a Kayak Questionnaire, gave verbal consent to participate in the study and didn’t have any injuries preventing them from participating.
Instrumentation: A Dansprint Kayak Ergometer was used to perform all kayak exercises at a standard resistance determined by the machine. A GoPro Hero 5 Black recording in 1080p at 60 frames per second with a linear field of view set 2.70 m away directly above from the ergometer was used to collect data in the transverse plane. An online metronome provided by a Google search for “metronome” set at 70 beats per minute was played during kayaking. A biomechanical data analysis kit including reflective markers and measuring devices were utilized throughout the experiment.
Familiarization: Subjects were asked to come into lab one week prior to data collection. This time was during Kayak Club hours (between the hours of 8pm and 10pm), when they would usually be kayaking. Each participant’s shoulder width was measured from acromion process to acromion process. This data was used to calculate the grip width for each participant on the ergometer paddle (grip width=130% of participant shoulder width). Tape was placed on the paddle to mark grip width and participants were instructed to keep their index fingers on it while paddling to maintain the same grip throughout the trial. Once seated on the ergometer, the seat was adjusted so the participant’s knees were at 55° of flexion according to medical convention. Across the length of the paddle, 1/8-inch p-cord was taped (representing the un-feathered trial). On the left hand side of the paddle, p-cord was taped also taped at 45° to facilitate the feathered condition. For the unfeathered condition, participants were instructed to keep the second metacarpal knuckle of their index finger of both hands on the p-cord that ran across the entire paddle (0°). This served as the neutral position. For the feathered condition, participants were instructed to rotate the second metacarpal knuckle of their left index finger off of the neutral p-cord to the 45° p-cord every time they performed a left-hand stroke. When they transitioned to the left stroke, they would hyperextend their right wrist, resulting in their left hand moving from the neutral p-cord to the 45° p-cord. Each participant paddled in each condition for a total of 2 minutes and 30 seconds. Strokes were regulated to a rate of 70 strokes/minute. Tester provided verbal feedback to participant to ensure they were paddling at the correct rate and to encourage them through the time.
Experimental: Participants came in during Kayak Club hours for data collection. Upon arrival, participants filled out the questionnaire and anthropometric data was collected. Participants then had reflective markers placed on the left and right acromion processes, the left medial epicondyle of the knee, and the left metacarpophalangeal joint. Based off of participant feedback from the familiarization trial, the grip width was too narrow for natural paddling. To adjust for this, researchers added 30% of the participants shoulder width to the grip width. For each condition, participants paddled with the same procedures used in the familiarization. The tester began recording video after they had begun paddling for multiple stroke cycles. Participants were not aware when filming started or stopped. Filming was concluded after three stroke cycles were completed.
Statistical Analysis: MAXTRAQ, a motion capture system that operates in two-dimensional data analysis was utilized for the digitizing and synthesizing of raw video captured. An example of a digitized subject can be found in the appendix of this study. After digitizing all markers for different condition trials, the shoulder angles and values for reach were exported into Excel. The angles generated from MaxTRAQ were adjusted to fit medical convention using the following formula: Medical Convention=Shoulder Angle-90°. Following that calculation, trunk ROM was computed for each subject in each condition using the following formula: Trunk ROM=Maximum shoulder angle-Minimum shoulder angle. The computer program, “IBM SPSS Statistics Data Editor” was used to perform a variety of statistical tests. Descriptive statistics were calculated for participants. A paired-samples t-test was completed between paddle condition (feathered and unfeathered) and core rotation. Another paired samples t-test was computed to compare maximum reach across the different paddle settings. Confidence level was set at 95% (alpha level = 0.05).
Descriptive statistics for age, height, and weight were collected (Table 1). A significant difference for core rotation was found between the un-feathered and feathered conditions (p<0.05) (Table 2). A significant difference for maximum forward reach was found between the un-feathered and feathered conditions (p<0.05) (Table 3). Figure 1 shows a time series graph demonstrating the core rotation of both paddle conditions for one full stroke cycle of one subject.
Table 1. Descriptive statistics of subjects.
Table 2. Differences of trunk ROM between unfeathered and feathered conditions.
*significant difference between conditions (p<0.05)
Table 3. Differences in maximum reach between unfeathered and feathered conditions.
*significant difference between conditions (p<0.05)
Figure 1. Time series graph showing amount of trunk rotation compared to time for both unfeathered and feathered paddle conditions. Data is shown for one full stroke cycle for one subject.
Contrary to the researchers’ hypothesis, the results of the present study showed a significant difference in both trunk ROM and maximum forward reach between kayakers using feathered and unfeathered paddle blades. When it comes to trunk ROM, the unfeathered condition (45.8083±10.66643 degrees) resulted in a significant increase in trunk rotation as compared to the feathered condition (42.2032±9.69120 degrees) (p=.041). Similarly, the unfeathered condition (22.5389±4.04205cm) resulted in a significant increase in maximum forward reach of the left hand when compared to the feathered condition (20.5274±4.63471cm) (p=0.003). As this was the first study to look at these kinematic variables in whitewater kayakers, there is little existing research to support these findings. However, these results are consistent with the notion that maintaining a neutral body position is a key factor in efficient paddling (3). In the feathered condition, hyperextension of the right wrist during a left paddle stroke likely led to increased flexion of the right elbow and extension of the right shoulder, thereby limiting the subjects’ ability to maximize core rotation and stroke length. Trunk ROM is crucial to power production during a stroke cycle as trunk rotator muscles can work over larger distances and for slightly longer periods of time as ROM increases. As maximum forward reach increases, so does the length of each stroke, especially the length of each power phase. This increase in power phase length means that each stroke is able to produce power for a longer period of time, leading to an increase in forward propulsion of the kayaker. This evidence suggests that use of un-feathered paddle blades while kayaking has the potential to maximize stroke efficiency.
The present study was not without its shortcomings. One shortcoming of the present study was the small sample size of only 6 subjects. It is possible that differences in average trunk ROM and maximum forward reach would be diminished for a larger sample size. Further research is needed in this field to determine whether there are correlations between ideal blade offset and variables such as age, height, and paddling experience. The present study also opens the door for further research to explore differences in kinetic physiological variables between kayakers using feathered and unfeathered paddle blades.
The researchers conclude that the use of un-feathered paddle blades leads to improved trunk ROM and maximum forward reach when compared to the use of feathered paddle blades in whitewater kayakers.
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Screenshot of MaxTraq analysis of core rotation and maximum forward reach: