Yes Glenn and Gary
– Last Updated: Feb-08-14 3:10 PM EST –
I agree with both of you. The semantics pertaining to the biomechanics of the forward stroke is kind of tricky. Terms such as push or pull usually grossly oversimplify or misrepresent what is actually going on.
I cannot find the site with the graphical depictions of the forward stroke I alluded to earlier. Perhaps I saw this in a video. In searching for it I came across a couple of other sites, one of which I had seen in the past. (Warning: some of this stuff is rather arcane and most people will probably wish to scroll on. What follows is intended for the certifiable.)
Here is an author who compares stroke mechanics with straight shaft and bent shaft paddles and makes a case for the 7 degree bent:
http://redrockstore.com/paddles/7degree.htm
I don't care much for his diagrams but it so happens that he uses language similar to what I did when he describes the straight shaft paddle in comparison to the bent shaft and says:
"Because the straight shaft paddle does not clear the body of a paddler like a bent shaft paddle does, the paddle-swinging dynamics change. The paddle gets lifted higher into the air before it's dunked in the water. Then, as it is pulled through the water by the blue arm, the green arm ends up actually pushing forward. This makes the blue arm point of contact act like a fulcrum or the "pivot point on a see-saw"."
As the diagrams show, the "blue arm" represents the shaft arm and the "green arm" the grip arm.
Years ago, Harry Roberts described the forward stroke thus:
"At entry the upper arm cocks rearward as if preparing to throw a jab. Simultaneously, the lower arm reaches forward while the torso rotates to increase the reach
of the lower arm. From this paddle entry position, the upper arm thrusts forward, the lower arm pulls rearward, and the torso rotates back to the neutral position. During the lower arm's pulling phase, the elbow remains straight and rigid."
I think most competitive paddlers have rejected this bottom arm straight and rigid style of paddling. I still hear people talking about the top arm punching forward from time to time.
I think this piece gives a much more accurate description of the forward stroke:
http://www.piragis.com/newsletter/canoestrokeefficiency.html
Notice that George Arimond advocates maintaining a bend in the lower arm elbow at approximately 140 degrees throughout the power phase of the stroke. So the bottom arm does not really flex during the power phase, but it is not maintained in full extension.
As for the top arm, George says:
"The top arm (i.e. the arm holding the top grip) moves with the bottom arm, but instead of pulling it presses in a forward/downward arc (see Figure 1)."
So he doesn't describe the top arm as either pushing or pulling but "pressing" forward and downward.
As for the thing I mentioned about not having to lift as much at the plant with a bent shaft paddle, take a look at Figure 1 in that last link which depicts the "Preparatory Position", the part of the stroke just before the paddle enters the water. The author points out that at this position the paddle shaft will be angled backwards from the horizontal about 40-50 degrees with a straight shaft paddle, but about 52-62 degrees with a 12 degree bent.
Sit in your chair and imagine yourself getting ready to plant the blade of a 12 degree bent shaft paddle. Put your arms and hands in that position. Now imagine planting the blade of a straight shaft paddle of about the same length, with the blade entering the water at the same angle and do the imaginary adjustment of your arms and hands that is necessary considering that the paddle shaft is now going to be angling back toward you by 12 additional degrees.
For me that involves increasing the flex in the grip arm elbow and moving both hands back toward my trunk, but also upwards, the grip hand much more than the shaft hand. That is what I meant by having to lift the straight shaft paddle more at the plant.
The article by George Arimond is actually based on a graduate research paper he did for Bemidji State University (where else?) back in 1980:
http://minds.wisconsin.edu/handle/1793/56800?show=full
He filmed 3 top marathon canoe racers with markers placed on their joint centers at wrists, elbows, shoulders, center point of head, and center point of torso. A stop action projector was used to project still frame images onto a computer digitizer tablet. I imagine that computer graphics capabilities have advanced a bit since 1980.
There were some interesting findings. Although there were more similarities than differences, he found significant variations in body mechanics from paddler to paddler, and even in the same paddler from paddling side to paddling side.
I reread this and will summarize some of his findings that I thought were significant.
1. For each paddler the in-water phase was about 60% of the total stroke duration, and the out-of-water phase about 40%.
2. During the in-water phase there was an axis of angular rotation or "pivot point" at the interface of the water surface and the throat of the paddle. The paddle shaft rotated forward and the paddle blade backward relative to this pivot point during the power stroke.
3.During most of the power phase this pivot point remained stationary relative to the camera and shore as the boat moved past it. But the pivot point actually moved forward relative to the shore somewhat at the start of the in-water phase, and slightly backward at the end. The fact that the pivot point moved forward somewhat during the plant argues that competitive paddlers do not load the paddle until the blade is fully immersed.
4. During the preparatory phase of the stroke the top forearm of the paddlers was extended to within 25 degrees of full extension. During the power phase the upper arm forearm showed a very gradual extension until reaching the end of the in-water phase. But there was significant fluctuation in this extension pattern, especially in the middle 40% of the in-water phase, and it showed no consistent comparative pattern test subjects or strokes. Moreover, one test subject when paddling on the left side (but not the right) demonstrated flexion of the upper arm forearm during the first part of the in-water phase, followed by extension in the latter part of the phase.
5. The paddlers all had some degree of lower forearm flexion at the preparatory phase, typically with the forearm at 155-170 degrees (10-35 degrees of elbow flexion). The lower forearm flexed further during the in-water phase by a mean of 43 degrees, so the paddlers typically ended the in-water phase of the stroke with the lower forearm at around 120 degrees on average. (Note that this finding is somewhat contradictory to the advice given by George Arimond in the prior link.) But again there was significant fluctuation of this lower elbow movement during the middle 40 percent of the in-water phase with no consistent comparative pattern of this fluctuating movement between strokes.
6. (This is I think the most significant finding.) At the preparatory phase the top upper arm was extended above the shoulder girdle and the bottom upper arm was at or below shoulder level. From this preparatory position both upper arms began flexion which continued throughout the in-water phase.
"The top and bottom upper arm movement was almost identical between subjects during the in-water phase, especially during the middle 40 percent of the water phase which provides greatest leverage for the paddle blade. Remember that during this middle 40% of the water phase there were significant variations in the manner in which the paddlers were extending or flexing their forearms.
7. All of the paddlers demonstrated some degree of torso rotation away from the paddle side and slight forward flexion of the trunk at the preparatory phase. The degree of torso rotation at the preparatory phase was observed to vary between paddlers. At the preparatory phase the upper shoulder was elevated and the lower shoulder depressed.
8. During the in-water phase the thorax rotated back toward the paddle side. The trunk flexed forward during the first 10-30% of the in-water phase, then extended until reaching approximately mid-air phase. But the subjects demonstrated considerable variation in the trunk flexion/extension movement. Mean degree of trunk flexion during the initial water phase was 9 degrees with 19 degrees of trunk extension occurring during the rest of the water phase and beginning of the in-air phase. During the latter part of the in-air phase the trunk flexed back to the starting position.
9. Movements of the head/neck were always opposite those of the trunk and seemed to initiate movements of the trunk, but there was considerable variation in movement patterns between individuals.
In his conclusion, George Arimond makes the following arguments:
"The uniform flexion of the upper arms was one of the most significant findings of this research. The importance of this movement is recognized in the fact that it occurs when the paddle blade is in a position to exert maximum leverage on the water. It was further noted that the upper arms showed the greatest degree of movement. Considering this large degree of movement and the paddle blade's maximum leverage angle, it is reasonable to suggest that the upper arm exerts the greatest leverage on the paddle. Movement within the trunk allows the upper arms to achieve a maximum range of flexion as well as maximum leverage. As the water phase beings, the trunk flexes, which assists the upper arms in submerging the paddle blade. As the paddle blade becomes submerged, the trunk extends, which allows the upper arms to continue flexion without uselessly submerging the blade deeper. The torso rotation and the shoulders' return action also aid the upper arm."
So although you could argue that the upper arm is "pushing" and the lower arm is "pulling" it seems that the most important driver of the stroke is the powerful upper arm flexion on the trunk, coupled with movements of the trunk (both rotational and flexion/extension) arcing the paddle shaft forward and downward while rotating the blade backward around a pivot point near the water's surface.
We think of the paddle shaft and paddle blade moving backward during the power phase but in reality what is happening during the power phase after the blade is fully immersed at the plant is that we are imparting a powerful angular rotation around an axis near the paddle throat as the boat moves past that axis (or pivot point). The motion of the paddle blade is more like that of a paddle wheel steamer with only one paddle blade than a blade being pulled back through the water.
And the upper arm motion during the paddle stroke is nothing like a jab or a rapid "thrusting forward" of the upper arm. In a jab the forearm is rapidly extended while the upper arm is simultaneous extended, rather than flexed.