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Accuracy'and'reproducibility'of'the'new'CycleOps'Hammer'Direct'Drive'Trainer'
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M.'Frémeaux1,'A.'Bouillod1,2,3,'E.'Brunet2,'G.'Soto-Romero3,4'&'F.'Grappe1,5'
1!EA4660,!C3S!Health!-!Sport!Department,!Sports!University,!Besancon,!France!!
2!French!Cycling!Federation,!Saint!Quentin!en!Yvelines,!France!
3!LAAS-CNRS,!Université!de!Toulouse,!CNRS,!Toulouse,!France!
4!ISIFC,!Université!de!Franche-Comté,!France!
5!Professional!Cycling!Team!FDJ,!Moussy!le!Vieux,!France!
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Key'words:'power!meter,!cycling,!home!trainer,!!
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Purpose:!The! measurement!of! power!output! (PO)!is! an!essential! element!in! cycling.!Three!
types!of!tools! can! measure!PO:!ergometers!(e.g.! SRM!Indoortrainer),!mobile! power! meters!
(e.g.!SRM,!Powertap!G3,!Powertap!P1,!Stages,!Garmin!Vector)!and!home-trainers!(e.g.!Wahoo!
KICKR)!(Zadow,! Kitic,!Wu,! Smith,!&! Fell,!2016),! Cyclus!(Rodger,! Plews,!McQuillan,! &! Driller,!
2016),! Lemond! Revolution! (Novak,! Stevens,! &! Dascombe,! 2015),! Velotron! (Abbiss,! Quod,!
Levin,! Martin,! &! Laursen,! 2009),! Axiom! (Bertucci,! Duc,! Villerius,! &! Grappe,! 2005).! The!
CycleOps!Hammer!Direct!Drive!Trainer!(Saris,!Madison,!USA)!is!a!new!home-trainer.!It!use!the!
technology!of!Powertap!G3!hub!(PowerTuned)!for!measuring!PO.!The!aim!of!this!study!was!to!
determine!the!accuracy!and!reproducibility!of!the!Hammer!in!comparison!with!the!Powertap!
P1!pedals.!We!hypothesized!a!lower!POHammer!than!POP1!considering!the!location!of!the!two!
power!meters!on!the!bicycle.!!
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Methods:! 3! cyclists! (age:! 23!±! 1! years! old,! body! mass:! 65.3! ±!2.5! kg,! height:! 174! ±!3!cm)!
performed!all!testing! sessions!on!their! personal!bicycle!fitted! with!the!Powertap! P1!pedals!
and! fixed! on! a! CycleOps! Hammer! Direct! Drive! Trainer.! To! investigate! the! accuracy! and!
reproducibility,! the! PO! of! the! two! power! meters! was! recorded! during! a! sub-maximal!
incremental!test!(150,!200,!250,!300!and!350!W).!For!each!PO!level!the!cyclists!!exercised! 3!
min!with!3!different!cadences!(60,!80!and!100!rpm)!(Bouillod,!Pinot,!Soto-Romero,!Bertucci,!
&!Grappe,!2016).!The!last!45s!of!each!measurement!was!analyzed.!Also,!the!cyclists!performed!
a!sprint!test!(3!sprints!of!8!s!with!three!different!resistances)!and!a!Wingate!test.!Before!each!
test,!the!power!meters!were!calibrated!according!to!the!manufacturers’!instructions.!!
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Figure' 1.! A:! correlation! between! POP1! and! POHammer,! B:! Bland-Altman! for! the! difference!
between!POHammer!and!POP1!during!the!sub-maximal!incremental!test!and!the!sprint!test.!The!
solid! line! represents! the! bias,! whereas! the! dashed! lines! represent! the! high! and! low! 95%!
confidence!interval!(CI).!
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Results:'For!all!data,!there!was!a!strong!correlation!between!POP1!and!POHammer!(r!=!0.99,!p!<!
0.001)!(Figure!1A).!The!Bland-Altman!analysis!(Figure!1B)!showed!a!bias!of!17!±!28!W!(95%!CI:!
12! and! 22! W)! for! the! Hammer.! Paired! t-test! have! shown! significant! difference! between!
POHammer!and!POP1!for!the!submaximal!incremental!test!(+0.9%,!p!=!0.008),!sprint!test!(+3.4%!
for!PO1-sec!and!+3.5%!for!PO8-sec!p!<!0.001)!and!Wingate!test!(+1.8%,!p!<!0.001).!!The!coefficient!
of! variation! (CV,! %)! was! 0.4%! for! both! the! Hammer! and! the! P1! during! all! submaximal!
incremental! tests.! For! the! Wingate! and! sprint! tests,! CV! was! the! same! (0.1%)! for! the! two!
systems.!The!reproducibility!was!tested!for!the!submaximal!incremental!test!because!the!PO!
was!fixed!by!the!Hammer.!Both!systems!have!the!same!intraclass!correlation!coefficient!(ICC!
=!1).!
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Conclusions:'The!main!findings!show!that!the!PO!provided!by!the!Hammer!must!be!treated!
with!some!caution!concerning!the!accuracy!whereas!the!Hammer!has!a!good!reproducibility.!
The! over-estimation! of! the! Hammer! can! be! explained! by! the! difference! of! measurement!
processes.!Theoretically,!the!Hammer!should!underestimate!PO!due!to!drive!train!frictional!
losses.!!Coaches!and!scientists!should!use!the!Hammer!with!some!caution!because!the!system!
overestimates! PO!when! it! increases.! One! the! other! hand,! the! reproducibility! is! good.! This!
point!is!valuable!when!coaches!compare!athletes!with!the!same!system.!Future!studies!should!
evaluate! the! accuracy! and! reproducibility! of! the! Hammer! in! comparison! with! a! dynamic!
calibration!rig!to!confirm!our!findings.!
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References'
Abbiss,!C.!R.,!Quod,!M.!J.,!Levin,!G.,!Martin,!D.!T.,!&!Laursen,!P.!B.!(2009).!Accuracy!of!the!velotron!
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http://doi.org/10.1055/s-0028-1103285!
Bertucci,!W.,!Duc,!S.,!Villerius,!V.,!&!Grappe,!F.!(2005).!Validity!and!reliability!of!the!Axiom!Powertrain!
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of!the!Cyclus!ergometer!and!the!Stages!power!meter!against!the!SRM!crankset!for!
measurement!of!power!output!in!cycling.!Journal*of*Science*and*Cycling,!5(December),!16–22.!
Zadow,!E.!K.,!Kitic,!C.!M.,!Wu,!S.!S.,!Smith,!S.!T.,!&!Fell,!J.!W.!(2016).!Validity!of!Power!Settings!of!the!
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