Abstract Laser class sailors have to hike out, i.e.hook their feet under the toe straps near the centrelineof the boat and hold their upper bodies over the edgeof the boat, to counteract the heeling forces generatedby the sails. To identify the parameters that are associ-ated with maximal hiking performance, this cross-sec-tional observational study measures various kneeextensor and hip Xexor muscle performance character-istics in 55 Laser sailors and correlates each with thearea-under-the-curve hiking moment over 3 min ofhiking on a hiking dynamometer (HM180). Our resultsshowed that higher body mass and HM180 were signiW-cantly associated with better race scores (Spearman’srho = ¡ 0.69 and ¡ 0.62, respectively, both P < 0.01)in male sailors who participated in the National Inter-
School Laser competition. Body mass (Pearson’s cor-relation coeYcient, r ¸ 0.95, P < 0.01 in both malesand females), maximum voluntary isometric strengthof the quadriceps (r ¸ 0.80, P < 0.01 in both males andfemales), and 3-RM knee extension strength (r ¸ 0.80,P < 0.01 in both males and females) were associatedwith a higher HM180. The correlations between height,abdominal muscle endurance (crunches), explosivelower body strength (vertical jumps), cycling time-to-exhaustion, quadriceps strength endurance, or isomet-ric quadriceps endurance with incremental loads(bucket test), and HM180 were weaker (r < 0.60).HM180 may be a useful performance indicator for Laserracing. Since strength measures correlated well withHM180, greater emphasis should be placed on develop-ing maximum strength in the quadriceps to improvemaximal hiking performance.
Keywords Dynamometer · Sailing · Maximum strength · Muscular endurance
Introduction
Although sailing as a competitive sport has beenaround for more than 150 years, sailing research is inits infancy. Compared to sports like soccer and trackand Weld, not much is known about the biomechanics,physiology, and even the performance indicators insailing.
As dinghies do not have ballast, they rely on thecrew’s bodyweight to counter the heeling forces gener-ated by the sails. Sailors hook their feet under the toestrap near the centreline of the boat, and hold theupper body over the edge of the boat (hiking) to exert
B. Tan (&)Changi Sports Medicine Centre, Changi General Hospital, 2 Simei Street 3, Singapore, Singapore 529889, e-mail: [email protected]
A. R. Aziz · W. Xie · J. Wong · K. C. TehSports Medicine and Research Centre, Singapore Sports Council, 15 Stadium Road, Singapore, Singapore 397718,
N. C. SpurwayCentre for Exercise Science and Medicine, University of Glasgow, Glasgow, G12 8QQ, Scotland, UK
H. MackieFaculty of Health and Environmental Sciences, UNITEC School of Sport, Auckland, New Zealand
C. Toh · F. K. FussSchool of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore, Singapore 639798,
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a righting moment and keep the boat upright. Therighting moment is a function of the sailor’s bodyweight and its moment arm relative to the mid-longitu-dinal axis of the boat (Putnam 1979). The heelingmoment, and hence the required righting moment, isgreatest when sailing upwind. In the Laser class, a sin-gle-handed dinghy that is raced in the Olympics, thereis no need to hike in light winds but as the windstrength increases to approximately 8 knots, the sailorstarts to hike out and is fully extended at approxi-mately 12 knots. Legg et al. (1999) reported that duringthe upwind leg of a simulated Olympic racecourse inwinds ranging from 5 to 15 knots, elite Laser sailorsspent an average of 94% of the time hiking. Hikingrequires sustained quasi-isometric actions (Spurway1999) of the knee extensors and hip Xexors forstretches of several minutes or longer, and severalauthors (Blackburn and Hubinger 1995; Spurway 1999;Vogiatzis et al. 1993) believe that the isometric actionof the hiking muscles restricts their own blood supplyfor the duration of the contraction, and the resultantischaemia rapidly causes fatigue. Since it is diYcult tosustain a full-hike for prolonged periods (e.g. 30 min),maximal hiking tends to be employed only at criticalperiods, e.g. oV the starting line and when attemptingto overtake or avoid being overtaken. Top sailors willbe able to hike maximally for longer, and hiking per-formance is an important determinant of the outcomeof each race in the physically challenging classes likethe Laser. In sailing regattas, penalty points areawarded for each Wnishing position, such that Wrstplaces have the least penalty points and last place hasthe most. Hence the lower the racing score, the betterthe race performance or result. Blackburn and Hubin-ger (1995) reported that in dinghy sailors, the correla-tion between hiking endurance (using a hiking bench)and performance in major regattas was 0.82.
While isometric quadriceps exercise (e.g. wall sits,hiking bench) would oVer the most speciWc drylandtraining for hiking sailors, prolonged isometric action isdiYcult to tolerate and (for the reason just stated) mayrestrict blood Xow through the muscles. Sailors havealso attempted circuit training, isoinertial resistancetraining, running (Wright et al. 1976), indoor rowing(Blackburn 2000b), and cycling to improve their hikingendurance. However, there is as yet no consensus onwhich form or combination of training is best forimproving hiking performance (Blackburn and Hubin-ger 1995; De Vito et al. 1993; Spurway 1999; Spurwayand Burns 1993; Shepherd 1990, 1997; Vogiatzis et al.1995) neither is there any agreement on the mostappropriate dryland test that can be used to predictand monitor hiking performance.
This cross-sectional observational study measuresvarious knee extensor and hip Xexor muscle performancecharacteristics—abdominal endurance (crunches), verti-cal jump power and height, cycling time-to-exhaustion,knee extensor maximal voluntary isometric contraction(MVIC), 3-RM knee extension strength, knee extensorstrength endurance, and hiking endurance with incre-mental resistance (bucket test)—in Laser sailors andcorrelates each with the maximal work done over3 min of hiking on a real-time hiking dynamometer, todetermine which parameter or parameters are mostclosely associated with maximal hiking performance.The authors are not aware of previous studies thathave used such a hiking dynamometer for this purpose.It is hoped that the results will help sailors and coachesidentify suitable gym or laboratory-based performancemeasures that can be used to predict maximal hikingperformance and monitor the hiking sailor’s progressduring training.
Method
Subjects
The sample consisted of 55 Laser sailors who racedeither the Laser Standard or Laser Radial. Volunteerswere sought by putting up an invitation to participatein the study at the notice board of the National SailingCentre, which is Singapore’s main racing hub. Forty-Wve raced at national level or below and ten racedinternationally. The subject characteristics aredescribed in Table 1. All subjects gave informed andwritten consent and the study was approved by theInstitutional Research Ethics Board.
Of the subjects, 20 males and 15 females partici-pated in the National Inter-School Laser Champion-ships, which was held at about the same time as thedata collection period. The racing scores (low-pointscoring, i.e. 1 point for Wrst, 2 points for second, etc.;overall score is the sum of the best four of the Wveraces; the lowest score wins) in the male and femalecategories were recorded. The races were all held inhiking conditions, with the wind velocity varyingbetween 8 and 12 knot.
Procedure
All tests and measurements were conducted in the labo-ratory from June to August 2002 (Singapore has a year-round racing season). Following a familiarization ses-sion comprising all the eight test measures to minimizeany learning eVect, the subjects underwent a Wrst test
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session comprising either tests 1–4 or 5–8 (tests num-bered in the order below) and then a second test sessioncomprising the remaining four tests. All three sessionswere conducted at least 48 h apart. Within each test ses-sion, all tests were conducted in numerical order, atleast 30 min apart. All subjects were instructed to main-tain their normal diets and training routines throughoutthe duration of the study and avoid any strenuous activ-ity in the 24 h prior to their test sessions.
Maximal hiking moment over 3 min
A hiking dynamometer (Fig. 1) comprising a speciW-cally manufactured hiking bench (with dimensionsidentical to a Laser hull) mounted onto a force plat-form (Advanced Mechanical Technology Inc., modelOR6-6-2000, MA, USA) was constructed for the pur-pose of this study. Prior to the test, the toe strap wasadjusted to each subject’s accustomed length. After aninterval of 5 min following a standardized warm-up,each subject was instructed to hike maximally (i.e.keeping the centre of mass as far away from the toestrap as possible) on the hiking dynamometer for all of3 min. All were given the option of hiking barefootedor with sailing shoes, using the hiking technique thatthey were most accustomed to, and were allowed tojerk, crouch, and alternate the body weight on eitherleg. Verbal encouragement was given throughout, withstrong encouragement to go all out during the initialpart of the test instead of pacing themselves over3 min. A real-time graph of the hiking moment versustime and a countdown timer were displayed on a com-puter monitor positioned in the direction of where theLaser’s bow would be, in full view of the subject.
The hiking moment (Fig. 1), deWned as M = GF(d1 + d2), was computed using a data acquisitionsoftware program speciWcally written for the hiking
dynamometer. Based on the principle of equilibrium ofmoment about a Wx pivot of a rigid body, M = Flegd2.Both Fleg and d2 were measured using the force plat-form. The software displayed instantaneous M againsttime on a graph. The area under the curve representedthe net moment over 3 min (HM180).
Abdominal muscle endurance (crunches)
Abdominal muscle endurance was reXected bycrunches performed to exhaustion (Blackburn 2000a).Lying on a mat with the knees Xexed to 90°, feetplanted on the mat but unrestrained, outstretched
Table 1 Subject characteristics
a Bivariate analysis involving race score was performed on this groupb Distance between the hip of a standing subject and the ground
All subjects Subjects who participated in National Inter-School Laser Championshipa
Body mass (kg) 64.0 § 9.4 53.9 § 7.9 60.8 § 6.1 52.3 § 5.2
Fig. 1 Force diagram for hiking dynamometer
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hands resting on top of the thighs, and head on the mat,each subject slowly curled up and touched the distaledge of the kneecap (marked by a tape) with theWngertips, then lowered the torso until the head madecontact with the mat. The crunches were performed ata rate of one every 3 s, guided by an electronic metro-nome (MX-338, Wave, Taiwan), until fatigued or fail-ure to complete a repetition in strict form (e.g. jerking,lifting the feet oV the mat, failing to touch the tape).The number of successfully completed crunches wasrecorded.
Vertical jump
The subjects performed two protocols of jump perfor-mance on a mat that was attached to a data collectioncomputer (Fitrojumper, Fitronic s.r.o., Bratislava, Slo-vak Republic). The Wrst is a single squat jump with nocounter-movement action. The best of three attempts(performed 60 s apart) was recorded and the verticaljump height was computed. In the second protocol,each subject repetitively performed counter-movementjumps for 15 s, from which the mean mechanical poweroutput of the lower body extensors over the 15 s wascomputed using the equation of Bosco et al. (1983). Alljumps were performed with the hands on the hips andthe feet shoulder-width apart, starting from 90° of kneeXexion.
Cycling time-to-exhaustion
Each subject cycled on an isokinetic cycling ergometer(Corival 400, Lode, Gronigen, The Netherlands) withthe seat height adjusted such that the knees were com-fortably extended and the ankle joints at a right anglewhen the pedal was at dead bottom centre. The sub-jects cycled within the range of 60–70 revolutions perminute (rpm) at 50 W for 3 min (this also serves as awarm-up), at the end of which the resistance wasimmediately raised to 6% of subject’s body mass. TheWgure of 6% was chosen to elicit a time to exhaustionof approximately 3 min. The subject continued crank-ing until volitional exhaustion or when the pedalcadence fell below 40 rpm. The subjects wereinstructed to remain seated, and strong verbal encour-agement was given throughout. The cycling time-to-exhaustion was recorded to the nearest second fromthe time the load was imposed until exhaustion.
Maximal voluntary isometric contraction
The MVIC was measured using the isometric mode ofthe Lido Active Isokinetic Multi-joint II dynamometer
(Loredan, USA). Each subject was seated with armsacross the chest and the edge of the seat just behind theknees. The padded ankle bars were positioned acrossthe ankle. The body was secured with thigh and bodystraps, with the knee and hip joints set at 130° and 104°,respectively (full extension being 180°). These jointangles correspond to the mean hiking body positionobserved during on-water Wlming by Blackburn(2000a). The subjects were instructed to extend theirknee maximally, without jerking. Each subject madethree maximal eVorts of 6 s on each side, with a rest of60 s between attempts. The sum of the highest peaktorque recorded on each side was reported for analysis.
Three repetition maximum (3-RM) knee extension strength
The 3-RM double-legged knee extension strength wasmeasured on a leg extension bench (Model 9784, Uni-versal Power, USA) using standard free weights (Aus-tralian Barbell Company, Australia and Eliko,Halmstad, Sweden). The 3-RM and not the 1-RM testwas used due to the lack of strength training experi-ence in the majority of the subjects. The sitting positionwas adjusted such that the knees were just oV the edgeof the seat and the starting position was at 90° of kneeXexion. The subjects were instructed to forcefullyextend their knees to a minimum of 160°, guided bya marker. Each subject warmed up using 50% of the3-RM load that was recorded during the familiariza-tion session. The 3-RM was determined within sixattempts using 5 kg increments or decrements, usingthe familiarization 3-RM as a guide. A 2-min rest inter-val was imposed between attempts.
Quadriceps strength endurance
Two-legged quadriceps strength endurance was mea-sured on the bench with free weights as in the 3-RMstrength test above. A load equal to 40% of the sub-ject’s 3-RM strength (rounded to the nearest 2.5 kg)was used. The test was performed at a rate of one rep-etition every 2 sec, with the aid of a timer (ChronomixProtime, Model CC8152, Sunnyvale, USA) until fail-ure. This was deWned as the inability to extend theknees to 160° within the repetition rate. A load of 40%of the 3-RM was the chosen as Vogiatzis et al. (1995)have concluded that on a laboratory simulator, withheavy sheeting, the quadriceps contract at 30–40% ofMVC. Mackie et al. (1999) reported that the upwardmean forces on the toe strap for elite Laser sailorswere 87% of predicted MVC. This is considerablyhigher than previous studies (Spurway 1999) and is
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possibly attributed to the indirect determination of theMVC.
Hiking endurance with incremental resistance (bucket test)
This is a maximal incremental test of hiking endurancebased on the protocol established by Blackburn(2000a). Each subject sat on an elevated padded benchwith the back of the knees touching the edge of thebench and the knees extended. A steel bucket with apadded strap attached in place of the handle (totalmass 1.4 kg) was hung over the ankles. The test beganwith a 15-kg plate placed in the bucket. The subjectsmaintained a knee angle of > 130° (the angle betweenthe tibia and the bench was checked every 60 s using agoniometer) as 5-kg plates (Eleiko, Halmstad, Swe-den) were added to the bucket every minute until thesubjects could no longer hold the bucket at the pre-scribed angle. The subjects braced themselves by grip-ping the bench and were allowed to shift the load fromone leg to another. Verbal encouragement was pro-vided throughout the duration of the tests. The sub-jects’ Wnal endurance time was recorded to the nearestsecond.
Statistical analysis
All descriptive data are presented as the mean § stan-dard deviation of the mean. The Statistical Package forSocial Sciences (SPSS 10.0 for Windows) was used forall statistical analyses. Bivariate analysis was con-ducted to determine the correlation between the racingscores (Spearman’s rho) or HM180 (Pearson correlationcoeYcient) and each of the other test measures. Bivari-ate rather than multivariate analysis was used because
the main purpose of this study was to identify perfor-mance indicators that were associated with race resultsor HM180, rather than to establish a causal link. Thetest–retest reliability coeYcient for the familiarizationand actual hiking moment measurements were com-puted using the Pearson product moment correlation.The signiWcance level was set at � = 0.05.
Results
The descriptive subject characteristics are shown inTable 1. The results of the various test measures areshown in Table 2, and the correlation coeYcients areshown in Table 3. The test–retest reliability for thehiking dynamometer between the familiarizationand actual HM180 measurements was 0.91 (P < 0.01).The Bland and Altman Limits of Agreement proce-dure showed that the mean diVerence between pairedHM180 measurements was ¡ 2,811 § 6,588, with threeout of 43 points (7%) beyond § 2 standard devia-tions.
Discussion
Others have identiWed the need to examine the rela-tionship between physical attributes and actual resultsof on-water racing (e.g. Legg et al. 1997; Niinimaa et al.1977), and found this diYcult because there are manynon-physiological factors that contribute to sailing per-formance, including tactical ability, technique, andwind-reading skills. Our results show that in hikingconditions, body mass and maximal hiking momentover 180 s (HM180) were the only two parameters thathad a correlation coeYcient of less than ¡ 0.6 with the
Table 2 Test results
All subjects Subjects who participated in National Inter-School Laser Championship
racing scores in males sailors who participated in theNational Inter-School Championships. None of theparameters correlated with race results in female sail-ors, and this may be because female sailors tend to sailtheir boats with a less physical technique (i.e. employ-ing a more static hiking style), or because the femalesailors were using the smaller and less physicallydemanding radial rig. Other tests that seem speciWc tohiking did not correlate with race scores. Hence, careshould be taken when attempting to predict sailing per-formance using land-based tests like crunches, verticaljump, cycling time-to-exhaustion, maximum strength,strength endurance, and the bucket test.
In order to predict racing performance, it is impor-tant that the test for measuring hiking performancesimulates on-water racing as closely as possible. Otherstudies (e.g. Blackburn 2000a; Walls et al. 1998) haveused designs that simulate the whole sailing course orthe upwind leg of the course, where sustained hikingover 10–20 min is required. Unlike previous studies,the hiking dynamometer used in this study aims tomeasure only short-term, all-out hiking over 3 min (i.e.HM180), rather than the whole upwind leg of thecourse. Such short bursts of hiking are important oVthe starting line, to overtake another boat, and to avoidfalling into another boat’s disturbed wind zones. Assuch, no attempt has been made to simulate sailingover waves, tacking, wind shifts, variable windstrengths, gusts, lulls, and tactical situations. In order tofurther isolate the contribution from the knee exten-
sors and hip Xexors, no loaded mainsheet or rudderarrangement was provided. It is noteworthy thatdespite focusing on short-term hiking performance,HM180 had a correlation coeYcient of ¡ 0.62 (P < 0.01)with racing scores in male sailors.
The hiking dynamometer has several advantagesover the conventional hiking bench: (1) the real-timefeedback serves as an incentive to hike harder; (2) thereal-time feedback also allows the user to see if his hik-ing technique is optimal, e.g. if he bends his knees orcrouches, the hiking moment decreases; (3) the dyna-mometer gives a quantitative output for all-out maxi-mal hiking that can be used to track performance, toset benchmarks, and to serve as a dryland test for sail-ing Wtness; (4) the hiking dynamometer is able to diVer-entiate between a sailor that hikes well and one thatcrouches in order to simply hike longer. On a conven-tional hiking bench, where hiking duration is used asthe objective measure, one can adopt a ‘lazy’ postureand hike longer, producing a misleadingly good ‘hikingperformance’; and (5) the hiking dynamometer has theability to assess the eVectiveness of dynamic hikingmovements. Over the last two decades, Laser sailinghas evolved such that competitive sailors have devel-oped and adopted eVective but demanding hiking tech-niques (e.g. straight-leg hiking) and are using morebody movements while hiking. Hiking on the Laser hasbecome a more dynamic rather than static activity. Thehiking dynamometer is able to capture and quantita-tively assess such new techniques.
Table 3 Correlation coeYcients between various parameters
Relative maximum voluntary isometric strength (N m kg¡1)
¡ 0.08 0.15 0.11 0.17
3-RM knee extension strength (kg) ¡ 0.47* ¡ 0.06 0.81** 0.82**Quadriceps strength endurance (reps) ¡ 0.51* ¡ 0.06 0.09 0.04Bucket test hiking time (s) ¡ 0.28 0.42 0.53** ¡ 0.18
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Of all the parameters measured, for both male andfemale sailors, it was body mass and the strength mea-sures that had strong correlations with all-out hikingperformance as reXected by HM180; these measureswere namely body mass (males 0.95, females 0.99),absolute maximum voluntary isometric strength of theknee extensors (males 0.81, females 0.81), and 3-RMknee extension strength (males 0.81, females 0.82).Indeed, Niinimaa et al. (1977) showed that the averagequadriceps force for the sailors (1,045 N) exceeded thatof oarsmen (741 N) and swimmers (720 N). Thatstrength measures showed such strong correlation withHM180 may be an indicator of the increasingly dynamic(as opposed to isometric) nature of Laser hiking. Possi-bly, a high level of maximum strength reduces the rela-tive isometric load of hiking, thus allowing the sailor tobetter tolerate and sustain isometric activity. Thestrong correlations suggest that the development ofisometric and isoinertial knee extension strengthimproves all-out hiking performance, but a prospectivestudy would be needed to establish a causal relation-ship and provide stronger evidence. Although sit ups,crunches, cycling, and the use of hiking benches arecommon training methods among Laser sailors, theresults showed that abdominal muscle endurance(crunches), vertical jump power and height, cyclingtime-to-exhaustion, and the bucket test had little or nocorrelation with HM180. This is despite the superiorspeed sit up performance found by Niinimaa et al.(1977) in sailors (42.6 reps min¡1) compared to thenorm (30 reps min¡1). It is noteworthy that the buckettest, which is a measure of isometric strength, had aweaker correlation (males 0.53, females ¡ 0.18) withHM180 compared to the 3-RM knee extension strength(a measure of isoinertial, maximum strength) (males0.81, females 0.82), again hinting that Laser hiking ismore dynamic in nature than previously thought.
It is also interesting to note that body mass was amuch stronger determinant of HM180 (correlationcoeYcient 0.95 in males and 0.99 in females) thanstanding height (correlation coeYcient 0.51 for malesand 0.50 for females) and trochanteric height (correla-tion coeYcient 0.22 for males and 0.40 for females).This may be because taller sailors could have diYcultycapitalizing on their increased leverage due to thelonger ‘lever arms’ of their musculoskeletal structure,which imposes greater loads on their muscles andmakes it more diYcult for them to extend their bodiesfully while hiking.
For the females, sailing experience had a correlationof 0.68 with HM180, indicating that the more experi-enced female sailors had superior maximal hiking per-formance. The experienced females could perhaps
have developed more eVective hiking techniques thanthere less experienced counterparts.
Conclusion
Body mass and maximal hiking performance (HM180)are associated with superior racing results in maleLaser sailors and hence HM180 may prove useful as aperformance indicator in Laser sailors. Sailors whohave greater body mass and greater isometric and iso-inertial strength in the knee extensors tend to havesuperior maximal hiking performance, whereas theassociation between explosive lower body strength,cycling endurance, quadriceps strength endurance, orisometric strength endurance and maximal hiking per-formance are weak or non-existent. This reXects therelative importance of developing maximum strengthin the hiking muscles during training.
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