Biomechanics of Rowing E-Book

Valery Kleshnev

• Herausgeber: Crowood
• Kategorie: Lebensstil
• Sprache: Englisch

Seitenzahl: 322

Veröffentlichungsjahr: 2020

Beschreibung

In rowing, races are often won in spite of, not because of, technique, and many misconceptions still preoccupy both rowers and coaches. This book explains the facts about rowing technique and will help you to find the right way to achieve your best performance. In this new edition, comprehensively updated to take account of the most recent developments in the sport The Biomechanics of Rowing offers a unique insight into the technical and tactical aspects of rowing, based on over twenty-five years experience of working with the best rowers and coaches all around the globe, a careful analysis of millions of data samples, and comprehensive biomechanical modelling with the aim of finding an optimal balance of variables. Topics covered include measurement; performance analysis; technique; ergometer rowing and, finally, rowing equipment and rigging.

Leseprobe

First published in 2016 byThe Crowood Press LtdRamsbury, MarlboroughWiltshire SN8 2HR

[e-mail]

www.crowood.com

This e-book first published in 2020

Second edition 2020

© Dr Valery Kleshnev 2016 and 2020

All rights reserved. This e-book is copyright material and must not be copied, reproduced, transferred, distributed, leased, licensed or publicly performed or used in any way except as specifically permitted in writing by the publishers, as allowed under the terms and conditions under which it was purchased or as strictly permitted by applicable copyright law. Any unauthorised distribution or use of this text may be a direct infringement of the author’s and publisher’s rights, and those responsible may be liable in law accordingly.

British Library Cataloguing-in-Publication DataA catalogue record for this book is available from the British Library.

ISBN 978 1 78500 778 1

CONTENTS

Preface to the Second Edition

1 Introduction

2 Measurements

3 Analysis

4 Technique

5 Ergometer Rowing

6 Rowing Equipment and Rigging

7 Performance Analysis in Rowing

8 Various Cross-Disciplinary Topics

References

Index

PREFACE TO THE SECOND EDITION

In the four years since the first edition of Biomechanics of Rowing was published, I received many questions from readers that were quite challenging sometimes, but it was always a very encouraging experience for me. It helped to identify new research areas and move our knowledge further forward. I would like to thank all the readers of my book, my colleagues, sport scientists, rowers and coaches for their interest, questions and very positive feedback.

The past four years were very busy for me, with continuous research and developments in rowing biomechanics, along with new data collection and analysis, which leads to new findings. Every month I published a newsletter, and each of them was an attempt to extend our expertise further in various directions. A lot of new data was collected in BioRow testing of rowers of many squads, and from races at World regattas. New methods were introduced in analysis of rower-boat system and blade work. A few new criteria of rowing technique were developed, such as Catch, Rowing Style and Finish factors, which helped make evaluation more precise and understandable for rowers.

This second edition was updated with the latest information and developments obtained after publishing the first edition. The basic concepts of efficient rowing technique remained unchanged as no contradictory facts were found, and rowing technique of most of the winning crews fit quite well to our criteria. The text was appended with new and more detailed definitions, the latest trends of the rowing speed, racing stroke rates and other extra information. Also, a few complicated or ambiguous pieces of the text were removed, including some predictions and target values, which were replaced by more objective trends and statistical data in rowers’ categories.

I do hope that these updates make the book easier to read and be comprehended by a wider audience of rowers and coaches. And, of course, your feedback is always welcomed.

    CHAPTER 1    

INTRODUCTION

This book is intended for rowers and coaches who want to improve their rowing technique, row faster and maximize their results in regattas, given their physical conditioning. Here I have tried to summarize my knowledge of rowing biomechanics, which was obtained from nearly thirty years of working with thousands of rowers and coaches from all around the world: from Europe to Australia, from China to the USA and Brazil. Many of them ended up being Olympic and World champions and I have learned a lot from them. This knowledge didn’t come as a divine revelation but is a product of extensive measurements and analysis, continuous attempts to solve many puzzles and exhaustive studies of the efficiency techniques of winning crews. Though inspiration is still important, I believe the only way to achieve it is through hard work and continuous thought.

I can say that my understanding of rowing biomechanics and technique is completely different now from that in 1986, which is when I finished my fourteen-year rowing career and started pursuing sport science. It was a very steep learning curve. In the beginning I had very limited instrumentation and had to rely on experts and literature, which mainly emphasized the importance of ‘smooth boat velocity’ and so on. If someone had asked me at the time ‘How should the best force curve look?’ my answer would have been quite evasive: ‘It is possible to win with various force curves.’ I just didn’t know. Now I realize how many mistakes we made at that time.

The logical question that I always ask myself is ‘Are you sure now that all these conclusions are true?’ The answer I give is: ‘They should be correct, on the basis of all the available evidence and its analysis. However, if new facts contradicting the theory should be found, or someone finds an error in the analysis, I have to revise it and develop a new theory.’ Of course, misconceptions are always possible, but at least I try to be open-minded.

For example, a few years ago I thought that a pair of horizontal forces at the handle and the stretcher might create a torque, which could lift the whole rower-boat system out of the water and decrease drag resistance. My colleague and friend Prof. Volker Nolte from Canada had an opposite opinion and counted only a rower’s vertical accelerations, but I was still hoping that a true lift force might exist. After a few quite sophisticated experiments (seeChapter 2.5.4), I have found that Volker was right: horizontal forces cannot be converted into vertical forces in the way I thought, but some data still remained unexplained. Suddenly, a solution came not from a sport scientist, but from a master rower and engineer, Tor Anderson from California, who suggested an effect of centripetal force, which we had both overlooked.

Very often, the reason for changing the concept is not a fault or mistake but due to new data being obtained when new instrumentation becomes available. For example, a few years ago the dominating winning race strategy was one that encouraged the fastest start. Now we can see a change in this trend, where more and more winners use a more even distribution of effort during the race.

Most of the information in this book could be found in the Rowing Biomechanics Newsletter (RBN), which I write and publish, and have done so monthly since 2001. My original reason to start this project was to keep my brain active in my speciality. Later it became a great tool not only for sharing ideas but also for their discussion and verification. Many thanks to all the contributors whose comments were very valuable in correcting errors and mistakes, obtaining new ideas and making the advance in rowing biomechanics possible. However, this book is not a simple compilation of newsletters. All the information was revised and structured and many contradictions accumulated over the years were corrected.

Quite a common approach as a way of improving rowing technique is to look at winning crews in an attempt to copy them, without considering why they are fast. However, nothing that’s worthwhile is ever easy, especially in rowing. Some crews are not winning just because they are; they win in spite of their technique by means of higher physiological power and stronger, better motivation. A large variety of rowing techniques could be found in winners of Elite regattas, so which one should you copy? Remember, a copy is always going to be worse than the original.

I propose a different approach, which is not as easy; it requires some extra efforts and brain power but will help you produce much more consistent and reliable results. What this book can offer you is an understanding of ‘how it works’, and why. This is a sort of mosaic, a completed puzzle, where the bits and pieces of rowing technique are placed in an organized manner and bound together through mechanical principles. This is not a simple system, and is sometimes controversial. You may try to improve one efficiency component, but lose more on another one. Therefore, using common sense is the rule of thumb here, and all ideas must always be verified empirically with actual rowing results.

This book is also for sport scientists: for people who want to measure numbers in rowing, relate them to technique and give specific advice to coaches and rowers. In general, sport biomechanics is a very specific science, much more than physiology, psychology or nutrition. Sporting technique is completely different in various sports, for example between rowing and swimming, canoeing and athletics, so there are very different analytical models and criteria of effectiveness, measurement methods and equipment. The biomechanical equipment is usually custom-made, and we can’t, as it were, ‘go and buy it in a shop’, unlike the skills of other sport scientists. It takes many years for a biomechanic scientist to obtain professional expertise in a specific area, and they usually can’t work across many sports and switch between them quickly, as other sport scientists can do.

Biomechanical models can be very complicated, with many important unknown variables. Sometimes, if you blindly follow an incorrect model, the outcome could even be counter-productive and decrease performance instead of improving it. Again, common sense and continuous verification of your ideas with practical results are absolutely necessary.

Rowing is a unique sport due to its technical complexity, which is defined by the following factors:

■ Rowing utilizes nearly all the muscles of the human body;

■ Rowing requires complex coordination of the rower’s movements, which is determined by many degrees of freedom: the three-dimensional pivoting oar, the moving seat and an unstable boat;

■ Coordination of the rowing movements becomes even more complex in crew boats, which require synchronization of the rowers’ motions;

■ Rowing is the only sport where the athlete moves backwards, which is not natural human movement and dictates inversion of the muscle sequence.

These factors make rowing a very technical sport and explain why rowing biomechanics is so important for developing an effective technique and achieving good results in this sport. Technique is not the only important component of rowing performance; a high physiological capacity is also compulsory. The top results can be achieved only through a combination of these two main factors together with mental toughness. There was evidence (comparison of erg scores and on-water results) showing that an effective technique could make the boat 3–5 per cent faster (10–15 seconds over a 2km race) at the same physiological power production, which is the difference in speed between gold medallists and sixth-placed B-finalists at Elite regattas.

In addition, rowing is a very productive sport in terms of measurements and science; rowing equipment allows many places where the sensors can be mounted to measure forces, angles, velocities and accelerations of the boat, oars and rower. Therefore, rowing biomechanics has quite a long history, originating at the end of the nineteenth century,13 when sensors were mounted on the oarlock and the rowing force was measured. Since that time, the measurement equipment has been continuously developing. Data acquisition technology is booming these days, since the beginning of the information age in the twenty-first century. However, numbers and curves would be useless without proper understanding of their meaning, how they are related to effective rowing technique and what sort of numbers are required for the best performance.

This book contains eight chapters:

1. This introduction;

2. Measurements – explains technology and meaning of biomechanical methods;

3. Analysis – the core theories behind rowing biomechanics;

4. Technique – practical applications of biomechanical information and knowledge;

5. Ergometer rowing – giving the specifics of using machines;

6. Rowing equipment and rigging;

7. Performance analysis – discusses races and rowing speed analysis;

8. Various cross-disciplinary topics – a brief overview of areas on the borderline of rowing biomechanics with other disciplines.

The purpose of this book is to help rowers and coaches to understand better the main biomechanical principles of effective rowing technique, to relate them to what they can see and what they can measure in rowing, and to show them some ways to improve technique and maximize the performance of their crews.

ROADMAP ON ROWING PERFORMANCE

Performance in rowing is a complex matter as it is in any sport. It requires high physiological power production, effective technique, mental toughness and smart management of an athlete’s lifestyle and training. The main purpose of biomechanics in rowing is improvement of technique. The main questions are:

■ What components of a rower’s skills can be analysed to develop optimal technique?

■ What biomechanical variables need to be measured to provide data for the analysis?

Fig. 1.1 Road map of rowing performance with the main components of biomechanics.

Fig. 1.1 schematically shows relationships between components of a rower’s skills and biomechanical variables. The real picture is more complicated, since the components of technique are interrelated and usually affected by many other biomechanical variables.

The road map of rowing biomechanics has three levels: measurement, analysis and performance. At the measurement level we collect information from sensors, process it (apply calibration, filters, averaging, and so on), store and feed it into the analysis level.

During analysis, we combine data from various variables, calculate derivative variables (for example power from measured force and oar angle) and values (for example maximum and average force), and produce some meaningful information. There are two separate areas at the analysis level: theory and practice. In the theory area, we produce and publish some common knowledge, such as average values in athlete groups, correlations, and normative criteria. In the practice area, we compare the acquired data with the normative criteria and produce recommendations for a specific athlete or crew, which are then fed into the performance level.

At the performance level we try to correct rowing technique with instructions obtained at the analysis level. Various methods of feedback can be used at this level: after a session, post-exercise and real-time feedback as well as various drills and rigging adjustments. After a technical correction is made, variations of rowing technique should be measured and analysed to check their impact and evaluate an athlete’s adaptability.

At the measurement level, there are three groups of variables related to very basic mechanical categories: time (stroke rate), space (drive length – rowing angles) and force (applied by a rower). Together these three variables produce the fourth mechanical category: energy (rowing power), which is very closely related to the average speed of the rower-boat system and, hence, with rowing performance. Below is a brief description of the main measurement areas:

■ The force curve defines the total impulse supplied by the rower as well as the dynamics of the system. An optimal force curve must be ‘front loaded’, full and not have any humps.

■ Coordination of the body segments’ velocities is related to the force curve and defines rowing style, which is the key component of technique.

■ Rigging defines the kinematics of oar and rower and through gearing ratio – the kinetics of the system. Lighter gearing makes the rower’s movements faster and, possibly, increases power production but reduces blade efficiency.

■ Oar handling skills of a rower could be evaluated using measurements of the vertical oar angle, which is related to the rigging (say, blade pitch and height of the gate) and could impact on blade efficiency.

■ Patterns of the boat velocity and acceleration during the stroke cycle result from the dynamics of the system and should be good indicators of quality of rowing technique.

To evaluate the numbers measured in these areas, we usually compare them with target values and curves, or what are called ‘Biomechanical Gold Standards’, developed based on the combination of two methods, fused together with creativity and common sense:

■ The Statistical method helps to relate measurements to rowers’ performance. Say, if one group of rowers have some common features of technique and always win medals and another group have similar physical qualities but row differently and are always missing finals, then we could conclude that the technique of the first group is more effective.

■ The Modelling method allows different variables to be related between themselves, and, importantly, with the rowing speed and rowing efficiency. For example, based on trends of the best results in world regattas, we could derive a ‘prognostic’ or ‘gold standard’ rowing speed, which 99.9 per cent guarantees a gold medal in the next Olympics. Then, knowing the drag factors of various boat types, we could derive the rowing power, stroke rate and length and the applied force required to achieve prognostic results.

    CHAPTER 2    

MEASUREMENTS

2.1 METHODS

2.1.1 Biomechanical Assessment Procedure

An important part of the biomechanics assessment procedure is the testing protocol, which must provide standard conditions and make results comparable between rowers and over the course of time. There are two major factors affecting rowing technique: the stroke frequency and fatigue. Therefore a test protocol was used consisting of two parts:

■ A step-test with increasing stroke rate: for example, 5–6 sections by 250m or 1 minute at 20, 24, 28, 32, 36 str/min with a free recovery of about 3–5 minutes and 30 second maximal effort;

■ Race length of 2,000m with full effort or specified percentage of it (say, at 95 per cent).

This test protocol was quite time-consuming (1–2 hours) and put a significant load on rowers. Therefore, a combined test protocol was designed, which enabled determination of both effects at once. The test consists of one continuous 2000m piece at racing force application, but various rates (seeTable 2.1).

This testing protocol received very positive feedback from rowers and coaches. This test was a good training load itself; the first half of it is performed at aerobic training intensity, which allows smooth transition to the second half with anaerobic intensity; only the last 500m is performed with stroke rates close to those used in racing. There can be some variation of this protocol for junior rowers and veterans. For example, sections N5 and N7 could be replaced with light paddling with corresponding reduction of the stroke rate for the next sections. The data samples are taken and averaged at every lap.

2.1.2 Data Processing

When rowing is measured with any telemetry system, the raw data looks like a long chain of waves where each peak represents one stroke cycle (seeFig. 2.1a). The number of strokes done (usually 200–250 for 2km test) multiplied by the number of channels (for example 48 channels, usually measured in an eight) makes the amount of data overwhelming and difficult to comprehend.

Fig. 2.1 Examples of raw data (a) and averaged force curves at various stroke rates (b).

A common way to represent cyclic rowing data is plotting it as an X–Y chart, where the X coordinate is the oar angle or handle position on a rowing machine. As an example, Fig. 2.1b shows the handle force curve in this way. Though this representation is more understandable and gives some impression about rowing technique, it is not useful for precise numerical evaluation, comparison and modelling of rowing biomechanics.

The key part of the BioRow data analysis is an algorithm of data averaging, which allows the conversion of information collected from an unlimited number of cycles into one typical stroke cycle. It was developed from 1991–199328 and was used for more than 25 years for data analysis both in a boat and on a rowing machine, as well as in other cyclic sports (canoeing and swimming). This method allows effective data analysis, storage and comparison, and very clear feedback and interpretation for rowers and coaches. Here it is explained in essence.

Fig. 2.2 Detection of the stroke cycle.

Firstly, the stroke cycle should be detected (Fig. 2.2). For this, we use oar angle data (or handle position on a rowing machine) and define the start of the stroke cycle at the moment when the angle crosses zero during the recovery (oars perpendicular to the boat axis, or the handle of a rowing machine passing over the knees). This point was chosen as it is the most idle period of the cycle, without sharp changes of the rower’s movement, where it is possible to pause naturally. Some other systems use the catch as the cycle start, which breaks apart this quick and very important phase of the stroke, and makes it difficult to analyse. In addition, it is not natural to pause the stroke at the catch. In crew boats, the cycle is detected using only one oar’s data for the whole crew (usually, of the stroke rower, port side in sculling), which allows perfect synchronisation of the data.

Fig. 2.3 Raw and averaged data of the handle force.

To check the validity of this method, various rowing criteria were derived for every stroke of the raw data (Vraw), then their averaged values (Vraw.av) were compared with the same criteria derived from the averaged arrays Vav. It was found that Vav values were slightly lower than Vraw.av, and for most criteria, the difference was within a range of 0.5 per cent. It is important that for average force the difference was much smaller (0.19 per cent) than for maximal force (1.11 per cent), which could be explained by deviation of the timing of the peaks in each stroke, which makes the average curve smoother with lower peak, but insignificantly affects the area under the curve.

In conclusion, the averaging algorithm works correctly and reliably and provides effective data analysis and feedback in rowing and other cyclic sports.

2.2 TIMING

Time is an absolute universal variable, which has only one dimension and direction. Therefore, timing can be related unambiguously to mechanical variables and make the analysis clear and effective. In rowing and also in many other sports, the result itself is measured in the time taken to cover the race distance.

2.2.1 Stroke Rate and Rowing Speed

Stroke rate (or cadence, frequency, pace, etc.) is the most obvious and commonly used timing variable in rowing as in many other cyclic sports. It is always measured by coaches and rowers during training and races and is used to define training and racing intensity. The stroke rate R is defined as a number of strokes N per unit of time T:

where T is in minutes – the commonly accepted unit of time in rowing, and R is strokes per minute denoted as 1/min, or min−1. Together with stroke length and force, the stroke rate is one of three components of rowing power, so it is one of the main determinants of performance in rowing. However, it is not possible to increase the stroke rate to infinity to improve rowing results; it is limited by mechanical conditions (inertial losses of energy increase with the stroke rate) and with neuromuscular abilities of rowers (a higher stroke rate would require a faster muscle contraction, which may be inefficient, and quicker coordination of movements). Therefore, it is important to find the optimal stroke rate, which maximizes rowing speed. This optimum may be different for different crews and boat types. Fig. 2.4 shows an example for two crews: in Crew A the maximal rowing speed was achieved at a stroke rate of 32 min−1, while in Crew B it continues to grow up to and beyond 40 min− 1.

Fig. 2.4 The effect of the stroke rate on the rowing speed and distance per stroke (DPS) in two rowing crews.

To evaluate dependence of the rowing speed on stroke rate and find its optimum, we introduced a method36 based on effective work per stroke (EWPS). Previously, distance per stroke DPS was used as a measure of the stroke effectiveness. However, DPS always decreases at higher stroke rates (even in the best crews), because the duration of the stroke cycle becomes shorter.

So, the question was: ‘What do we need to preserve as the stroke rate increases?’ It was decided that the main objective is to sustain the application of force F, of stroke length L, and of mechanical efficiency E. The effective work per stroke, EWPS, integrates all these variables and is used as the basis of the method:

EWPS

∼

F * L * E

(2)

The rowing speed V and rowing power P are related as following:

where DF is some dimensionless factor depending on the boat type, displacement, weather conditions and blade efficiency. Therefore, EWPS can be expressed in terms of power P, stroke cycle time T, rowing speed V, stroke rate R:

For the two sections of rowing with different stroke rates (R1 and R2), if the value of EWPS was maintained constant and also DF1 and DF2 are the same, then ratio of the rowing speeds (V1 and V2) must be:

Correspondingly, the ratio of DPS (distance per stroke) values can be expressed as:

Fig. 2.5 Dependence of the rowing speed and DPS on the stroke rate (a), analysis of EWPS (b).

To use this method, we do not need to know drag factor DF, because it is assumed constant for all samples analysed. However, this is applicable only for the same boat, rowers and weather conditions, which is a limitation of the method. Fig. 2.5a illustrates the equations and represents dependencies of the rowing speed and DPS on the stroke rate.

The most practically convenient application of the method is the definition of ‘prognostic’ or ‘model’ value of the speed Vm for every stroke rate:

where V0 is usually average of all samples of the race or step-test. Then, the actual speed in each sample Vi can be compared with the ‘model’ Vm and its deviation D calculated:

If D is positive, then EWPS in this sample was relatively higher than average over the whole race or test (Fig. 2.5b) and vice versa. This method can be used for race analysis in cyclic water sports (rowing, swimming,20 canoeing), employed for evaluation of the strength- and speed-endurance using a step-test and does not require sophisticated equipment (only a stopwatch or StrokeCoach).

should be used to calculate normative splits for various stroke rates. For example, your target for a 2km ergo race is 6:00 at the rate of 36 min − 1. If you can train at the rate 18 at a split of 1:53, this means your muscles are ready to produce the same amount of work per stroke, as required for your target result and rate.

2.2.2 Rowing Rhythm

Fig. 2.6 Dependence of the rowing rhythm on the stroke rate.

2.2.3 Case Study: Factors Affecting the Rhythm

Is it better to have the rowing rhythm higher or lower? Many coaches believe that a lower rhythm is more efficient and ask their crews to shorten the drive time, but does that make sense? Biomechanical variables of two M1x were analysed at the same stroke rate of 32.5 str/min (Fig. 2.7). Sculler 1 (red) had a rhythm of 49.5 per cent or 0.91s drive time compared to Sculler 2’s (blue) 52.5 per cent and 0.97s correspondingly; that is, the second one had a 3 per cent higher rhythm and 0.06s longer drive time. The reason for this difference was quite simple: Sculler 1 had a total oar angle of 107.5 degrees while Sculler 2 had 116 degrees; that is he had an 8.5 degree longer stroke length. This fully explains the difference in rhythm and drive time since the average handle velocity during the drive (= drive length / time) had the same value of 1.73 m/s in both scullers. This happened in spite of Sculler 1 applying a 3.9 per cent higher maximal force and 2.6 per cent higher average force than Sculler 2.

Fig. 2.7 Biomechanical variables affecting the rowing rhythm.

What other biomechanical features are related to this difference in rhythm and stroke length? During the recovery, Sculler 2 has to move the handle much faster (Fig. 2.7, point 1) to cover a longer distance in a shorter time, so his average handle speed was 11.7 per cent higher. This was impossible without faster seat/leg movement (2). At the catch, Sculler 2 changes direction of the seat movement much quicker than Sculler 1, slightly before his handles change direction (3). Contrarily, Sculler 1 uses his trunk even before the catch (4). Consequently, the boat acceleration of Sculler 2 has an earlier and deeper negative peak (5), but higher first positive peak (6), so his boat and stretcher move relatively faster (7), creating a better platform for acceleration of Sculler 2’s mass (‘trampoline effect’, seeChapter 3.2.5).

Other technical advantages of Sculler 2 were:

■ More effective return of the trunk at the finish (8);

■ Better blade work at the catch (9) and finish (10);

■ Faster force increase up to 70 per cent of max. (11);

■ 1.5 per cent lower variation of the boat velocity (0.5s gain over 2km);

■ 3.3 per cent higher rowing power because of longer drive.

As a result, the rowing speed of Sculler 2 was 5.9 per cent higher (6:34 for 2km) than Sculler 1 (6:57) as well as his performance (world medallist compared to third finalist for Sculler 1). Conclusion:The rhythm and drive time cannot be changed voluntarily as they depend on the stroke rate, length and rowing speed. The stroke length is the main factor affecting the rhythm. There are other factors, which may affect rhythm (shape of the force curve and depth of the blade), which we may study in the future.

2.3 ANGLES

2.3.1 Horizontal Oar Angle and Drive Length

The horizontal oar angle is one of the most important variables in rowing biomechanics, which defines the amplitude of the oar movement in a horizontal plane. It is measured from the perpendicular position of the oar relative to the boat axis, which is zero degrees (Fig. 2.8a). The catch angle is defined as the minimal negative angle, the finish angle is the maximal positive angle and the total angle is the difference between finish and catch angles. The horizontal oar angle is used for triggering the stroke cycle, which occurs at the moment of zero oar angle during recovery.

The oar angle can be measured at the oar shaft or at the gate, and these two methods produce slightly different results (Fig. 2.8b). The total angle measured at the gate was found to be 4–5 degrees larger than the total oar angle, mainly because of finish angles. There are two main reasons for this difference (Fig. 2.9):

Fig. 2.8 Definitions of the horizontal oar angles (a), comparison of the angle measurements at the oar and at the gate (b).

Fig. 2.9 Differences in measurements of the oar angle at the oar shaft and at the gate.

1. A bend of the oar shaft. When force increases at the first half of the drive, the oar shaft bends and its angular velocity is slightly faster than at the gate. At the second half of the drive the oar extends, and its rotation appears to be slower than the gate rotation. This is the reason for the small difference in the catch angle and has no effect on the finish angle, because the force at this point is minor.

2. Backlash of the oar sleeve in the gate is the main contributor to the difference in the finish angle. It depends on the geometry of the gate, sleeve and button, and also on coordination of feathering along with horizontal and vertical movements of the oar. The backlash does not create any inefficiency because the blade is already out of the water and no propulsive force is produced at that moment.

The method of measuring the angle (at the oar, or at the gate) usually corresponds to the method of measuring the force and is determined by the following factors:

■ If the target is the geometry and kinetics of the rower’s movement then the oar angle and force are the best choice. The main advantage of this method is accurate determination of the handle position and power production of the rower.

■ If boat kinetics and propulsive forces need to be measured then gate angle and force are quite useful for defining force components at the pin. However, the rower’s power cannot be estimated accurately because of unknown actual leverage of the oar.

The drive length is defined as the length of the arc Larc made by the middle of the handle, and related to the amplitude of horizontal angle A and actual inboard Lin.a as:

The actual inboard Lin.a is the distance from the pin (centre of the oar rotation) to the middle of the handle, and it is related to the normally measured inboard Lin (from the collar to the top of the handle) as:

where Wg/2 is half the gate width (2cm for the standard gate) and Wh/2 is half the handle width, which is set at a standard 6cm in sculling and 15cm in rowing. It is important to maintain this standard, because it makes drive length comparable in sculling and rowing, and is used for calibration of the handle force and provides correct calculations of work per stroke and rowing power.

Oar angles are longer in sculling boats (Table 2.2), because of shorter inboard length, and for the same reason the angles are slightly longer in big boats. Male and open-weight rowers row 2–4 deg longer catch angles than females and light-weights, while finish angles are quite similar in these categories.

A common question, ‘What are the target angles for the best performance?’, is not easy to answer, because top rowers became successful using various ratios of the stroke length (angles) to the stroke rate. Last few years, higher racing stroke rate became fashionable (seeChapter 7.3), so the stroke length looks shorter than before. From our experience, top rowers use catch angles about + 1 SD longer than average (56–58 deg in sweep, and 66–68 deg in sculling), but finish angles were found quite close to the average.

Fig. 2.10 Stroke length at various stroke rates.

Usually, the maximal stroke length occurred at a stroke rate of around 24 str/min (Fig. 2.10). The length became 2–3cm shorter at lower rates, and this is probably related to lower inertia forces which help to stretch muscles and ligaments at catch. The reduction of the stroke length is more significant at higher rates, especially in big boats: in 4 x and 8 + it was 10–11cm shorter at a stroke rate of 40 str/min relative to 24 str/min, while in smaller boats it was only 6–7cm shorter.

2.3.2 Vertical Oar Angle

Vertical oar angle is an important variable that could be used for evaluation of the blade work in the water. Fig. 2.11a shows the reference system used for the measurements of the vertical angle (VA). For practical reasons, the zero vertical angle was defined at the centre of the blade at water level. A positive direction means the blade is above water level, and a negative direction means the blade is below water level.

Fig. 2.11 Definitions of the vertical oar angle (a), and sensor for measurement of 2D oar angles in BioRowTel system (b).