Effect of Sodium Phosphate Supplementation on Cycling Time Trial Performance and VO 2 1 and 8 Days Post Loading

Transcription

1 Journl of Sports Science nd Medicine (2014) 13, Reserch rticle Effect of Sodium Phosphte Supplementtion on Cycling Time Tril Performnce nd VO 2 1 nd 8 Dys Post Loding Cmeron P. Brewer, Brin Dwson, Kren E. Wllmn nd Kym J. Guelfi School of Sport Science, Exercise nd Helth, The University of Western Austrli, Perth, Western Austrli, Austrli Abstrct This study exmined the effect of 6 dys of sodium phosphte (SP) (50 mg kg FFM -1 dy -1 ) or plcebo (PL) supplementtion in trined cyclists on either 100 kj (23.9 Kcl) (~3-4 min) or 250 kj (59.7 Kcl) (~10-12 min) time trils performnces both 1 nd 8 dys post-supplementtion. Trils were performed in counterblnced crossover design, with 28-dy wshout period between supplementtion phses. No significnt differences, moderte-lrge ES (d) or likely (or greter) smllest worthwhile chnge (SWC) vlues were recorded for time to completion nd men power output on dys 1 nd 8 post-supplementtion, both within nd between SP nd PL for either the 100 or 250 kj (23.9 or 59.7 Kcl) trils. In the 100 kj (23.9 Kcl) tril (only) first minute VO 2 tended to be higher in SP8 thn both PL8 (d = 0.60; 88/10/2 SWC) nd SP1 (d = 0.47: 82/15/3 SWC), s ws men VO 2 (PL8: d = 0.77; 93/6/1 SWC nd SP1: d = 0.84; 90/8/3 SWC). No significnt differences were found for hert rte, rtings of perceived exertion nd blood lctte post-exercise within or between ny trils, while serum phosphte vlues were not different before or fter supplementtion with SP or PL. In conclusion, this study showed tendency for incresed VO 2 in short durtion (100 kj/ 23.9 Kcl: ~3-4 min) cycling test on dy 8 fter SP supplementtion, but no differences in 100 or 250 kj (23.9 or 59.7 Kcl) time trils performnces were observed. Key words: Serum phosphte, lctte, hert rte, RPE. Introduction Sodium phosphte (SP) is n ergogenic id tht hs previously been reported to improve erobic cpcity by % (Brewer et l., 2013: Cde et l., 1984; Czub, et l., 2008; 2009; Kreider et l., 1990; 1992; Stewrt et l., 1990), with some benefits lso found for endurnce performnce (Follnd et l., 2008; Kreider et l., 1992). In reltion to these benefits, number of possible mechnisms hve been proposed. Specificlly, these re: (i) incresed 2, 3 diphosphoglycerte (DPG) concentrtions, which cn ultimtely fcilitte greter relese of oxygen from hemoglobin (Hb) to the muscle (Cde et l., 1984; Chnutin nd Curnish, 1967; Frber et l., 1987; Stryer, 1988); (ii) incresed extrcellulr nd intrcellulr phosphte vilbility, resulting in greter glycogenolysis, glycolysis nd oxidtive phosphoryltion, which my increse the rte of ATP production nd enhnce cellulr metbolism during exercise (Chsiotis, 1988; Lichtmn et l., 1971; Thompson et l., 1990); (iii) incresed intrmusculr concentrtions of ATP, PCr, nd inorgnic phosphte, llowing for more rpid restortion of these molecules during erobic nd nerobic exercise (Chsiotis, 1988; Stryer, 1988); (iv) incresed crdic muscle contrctility (Czub et l., 2008, 2009; Kreider et l., 1992); nd (v) incresed buffering cpcity of hydrogen ions (Avioli, 1988). To dte, only few studies hve investigted the effect of SP on ctul exercise performnce, with these typiclly limited to tsks of prolonged (> 20 min) durtion, including 5-mile run (Kreider et l., 1990), 16.1 km (Follnd et l., 2008) nd 1000 kj (238.7 Kcl)/40 km cycling time trils (Brewer et l., 2013; Kreider et l., 1992). Currently, no studies hve investigted the effect of SP on exercise tsks of shorter durtion, despite the potentil for enhnced performnce in these types of ctivities. Bsed on the proposed mechnisms of SP loding, such s incresed H + buffering, incresed nerobic glycolysis, PCr resynthesis nd ATP production, thletes my benefit from exercise metbolism during shorter durtion, higher intensity exercise. In support of the bove mechnisms, we recently reported significntly higher power outputs during the erlier stges of 1000 kj (238.7 Kcl) cycling time tril (250 kj/ 59.7 Kcl nd 500 kj/ Kcl time points) following SP supplementtion (Brewer et l., 2013). This rises the question of whether SP loding my benefit exercise performnce of < 15 min in durtion. Another spect of SP supplementtion tht remins uncler is the durtion of ny ergogenic effect. Studies hve typiclly employed supplementtion protocol involving ingestion of 3-4 g dy -1, split into 4 equl doses, for period of 3 to 6 dys, with n exercise test completed on the following dy (Cde et l., 1984; Follnd et l., 2008; Kreider et l., 1990; 1992; Wllce et l., 1997). However, some reserch suggests tht the effects of SP loding my persist for some time fter cesing supplementtion. For exmple, Cde et l. (1984) reported lingering increse in 2, 3 DPG levels up to two weeks post-supplementtion. We lso recently reported n dditionl increse in VO 2pek, compred with both bseline nd the first phse of supplementtion, following second phse of supplementtion with SP. This second phse occurred either 15 or 35 dys fter the initil loding phse, indicting tht the ergogenic effects my be mintined for n extended time nd potentilly dditive upon subsequent supplementtion (Brewer et l., 2013). Czub et l. (2009) lso found tht when SP supplementtion (fter initil loding) ws continued t lower doses for further 3 weeks, VO 2mx ws mintined t higher thn pre-loding levels. Whether SP supplementtion cn ffect exercise performnce for up to week or more postloding remins to be exmined. Therefore, the purpose of this study ws to investigte the effects of 6 dys of SP Received: 02 December 2013 / Accepted: 17 Februry 2014 / Published (online): 01 September 2014

2 530 Sodium phosphte, VO 2 nd cycling supplementtion on short durtion (~ 3-4 min nd min) cycling time tril performnce both 1 nd 8 dys post-loding. Methods Prticipnts Twenty-one competitive mle cyclists volunteered for this study, lthough two filed to complete ll testing phses due to unrelted injury. Prticipnts were rndomised into two groups, with one group completing 100 kj (23.9 Kcl) time tril protocol (n = 10, men ± SD: ge 30.2 ± 9.2 y; body mss 81.9 ± 10.2 kg; height 1.84 ± 0.08 m; body ft 14.2 ± 5.2 %; VO 2pek 5.29 ± 0.39 L min -1 ; yers of competitive cycling 4.9 ± 2.2 y) nd the other 250 kj (59.7 Kcl) time tril protocol (n = 9, men ± SD: ge 27.8 ± 8.8 y; body mss 79.6 ± 12.4 kg; height 1.82 ± 0.09 m; body ft 10.7 ± 4.4 %; VO 2pek 5.38 ± 0.63 L min - 1 ; yers of competitive cycling 8.2 ± 5.9 y). The Humn Reserch Ethics Committee of the University of Western Austrli (UWA) pproved the study nd ll prticipnts provided written informed consent. None hd tken ny other nutritionl supplements for t lest 2 months prior to (or during) this study. The study ws conducted during the Western Austrlin competitive cycling seson; ech prticipnt ws required to mintin consistent trining volume over the study durtion. This comprised (men ± SD) 271 ± 90 km wk -1 (100 kj/ 23.9 Kcl group) nd 289 ± 188 km wk -1 (250 kj/ 59.7 Kcl group) of rod cycling, with n dditionl 8.6 ± 5.4 nd 12.2 ± 4.1 h per week of cross trining in other physicl ctivities, for ech group respectively. Experimentl design Ech prticipnt completed n initil fmiliristion session, followed 48 h lter by bseline ssessment of VO 2pek. Next, prticipnts completed two seprte phses of testing in counterblnced, double-blind, crossover design over 3-month period. Ech phse involved 6 dys of supplementtion with SP or plcebo (PL), with either 100 kj/ 23.9 Kcl or 250 kj/ 59.7 Kcl cycling time tril completed firstly on dy 7 (i.e. the dy fter cesstion of supplementtion) nd then repeted 7 dys lter (i.e. 7 dys fter finishing supplementtion). A 28-dy wshout period, beginning fter the lst dy of supplementtion, ws completed before the next phse of supplementtion nd testing commenced. Fmiliristion session Here, medicl nd trining questionnires were completed, height nd body mss were recorded, nd body composition (percentge body ft nd ft free mss) ws ssessed using dul energy X-ry bsorptiometry scn (DEXA; Lunr Prodigy, encore 2004, GE Medicl Systems, Mdison, Wis., USA). Prticipnts then completed the initil stges of grded exercise test (first three incrementl worklods while brething through mouthpiece), nd following 5 min of recovery, completed either (100 kj/ 23.9 Kcl or 250 kj/ 59.7 Kcl) cycling time tril (depending on their rndomistion) while brething through the sme mouthpiece, in order to become ccustomed to the tests nd procedures to be used during the subsequent experimentl trils. All exercise testing ws performed on n ir-brked cycle ergometer (Evolution bicycles, Geelong, Austrli), linked to customised computer progrm for the determintion of power output nd totl mechnicl work (Cyclemx version 6.3, School of Sport Science, Exercise nd Helth, University of Western Austrli). This ergometer hs fn bldes ttched to flywheel, which displces ir s the wheel turns, mking resistnce proportionl to pedlling rte. In ddition, the cycling ergometer hd six gers which prticipnts were ble to djust, llowing for individul resistnce nd cdence to be set independently for ech performnce test undertken. This setup ws intended to mximize ecologicl vlidity by replicting the vrition in pedl rte nd gering experienced during n ctul rod cycling time tril. Assessment of VO 2pek Pek erobic cpcity ws ssessed 48 h fter the introductory session using n incrementl cycling exercise test, strting t 150 W nd incresing by 50 W every 3 min, with 1 min of rest between stges to llow for cpillry blood smpling for lctte determintion (35 µl; ABL 725, Rdiometer, Copenhgen, Denmrk). The test ws continued until volitionl exhustion or when the prticipnt could no longer mintin the required power output. Hert rte ws recorded 30 s prior to the end of ech 3 min exercise intervl. During exercise, prticipnts brethed through mouthpiece connected to computerised gs nlysis system, incorporting ventilometer (Universl ventiltion meter, VcuMed, Ventur, Cliforni, USA), clibrted before the test using 1-litre syringe ccording to mnufcturer s instructions. Expired oxygen nd crbon dioxide concentrtions were nlysed using Ametek gs nlysers (Applied Electrochemistry, SOV S-3A11 nd COV CD-3A, Pittsburgh, PA, USA), which were clibrted immeditely before nd verified fter ech test using certified gs mixture of known concentrtions (BOC Gses, Chtswood, Austrli). Both the ventilometer nd gs nlysers were connected to computer tht mesured nd displyed vribles (VO 2 nd V E ) every 15 s, which were mesured throughout the test. Individul VO 2pek vlues were clculted using the sum of the four highest consecutive 15 s VO 2 vlues recorded during the test. Supplementtion protocol Prticipnts were given either tribsic sodium phosphte dodechydrte (Chllenge Chemicls Austrli, Kwinn, Western Austrli; 50 mg kg FFM -1 dy -1 ) or plcebo (PL) mix of glucose nd tble slt (rtio 9/1). The PL included slt in order to msk the tste of the supplement ingested, s SP hs slightly slty tste. Ech supplement ws ground into fine powder to mke them indistinguishble from ech other. This dily mount ws divided into four equl doses nd ingested with mels, to ensure optiml bsorption, over the course of ech dy (4-5 h intervl) in opque cpsules (Melbourne Food Depot, Est Brunswick, Victori Austrli) for six-dy period until 8 h prior to the scheduled exercise test. Ech cpsule dose ws emptied into glss nd consumed with 15 g of Powerde powder (Coc-Col Amtil, Austrli) tht

3 Brewer et l. 531 hd been dissolved with ~ 300 ml of wter. This procedure ws followed in order to prevent gstrointestinl upset (experienced in prior pilot testing with SP nd reported by West et l., 2012) nd to msk the tste. 100 kj (23.9 Kcl) nd 250 kj (59.7 Kcl) time trils protocol Prticipnts refrined from exercise for 24 h prior to ech time tril, with exercise testing tking plce t the sme time of dy (± 1 h) to control for circdin vrition. They were lso sked to record ll food nd drink intke, including the type of food, mount consumed nd timing of consumption, in diry for the 24 h prior to ech time tril. Copies of this informtion from the first tril were provided to ech prticipnt prior to ech subsequent tril, with the requirement for them to replicte this energy intke s closely s possible. Complince ws confirmed upon rrivl to the lbortory for ech time tril fter inspection of the food diries by the investigtor. As previous reserch hs used 500 kj cycling time tril to pproximte distnce of 20 km (Peeling et l., 2005), trget worklods of 100 kj (23.9 Kcl) nd 250 kj (59.7 Kcl) were chosen to represent ~ 4 km nd 10 km, respectively. When performing ech time tril, prticipnts cycled in n isolted room with no externl influences (i.e. music or other distrctions). A computer screen llowed prticipnts to see the mount of kj left to complete (which counted down from 100 kj/ 23.9 Kcl or 250 kj/ 59.7 Kcl), but kept them blinded to their power output nd durtion of performnce. During exercise, prticipnts brethed continuously through mouthpiece connected to computerised gs nlysis system (s described previously) for VO 2 mesurement. Blood smples (35 µl) were collected from the erlobe t rest nd immeditely post- exercise for mesurement of lctte using blood gs nlyser (ABL 725, Rdiometer, Copenhgen, Denmrk). Hert rte (Polr Electro OyProfessorintie, Kempele, Finlnd) nd rting of perceived exertion (RPE; Borg, 1982) were recorded immeditely fter ech time tril. Determintion of serum phosphte Prior to the fmiliristion time tril nd following ech 6-dy supplementtion phse, venous blood smple ws tken from n ntecubitl vein (BD Vcutiner SST II Advnce) to mesure serum phosphte levels. Smples were left to clot t room temperture for 60 min prior to being centrifuged t 1000 g t 4 C for 15 min. The serum obtined ws stored t -80 C for lter nlysis, with serum phosphte determined using n Abbott Architect c16000 nlyser, using the specified Abbott regents (Abbott Lbortories, Abbott Prk, IL 60065, USA). Observed coefficients of vrition were 4.2% t level of 0.95 mmol l -1 nd 2.0% t level of 2.95 mmol l -1. Sttisticl nlysis The post-supplementtion trils were designted SP1 nd PL1 (dy 1 post supplementtion) nd SP8 nd PL8 (dy 8 post supplementtion). The effect of supplementtion on time tril performnce nd ssocited physiologicl nd perceptul vribles (HR, lctte, VO 2, V E nd RPE) ws nlysed using 2-wy, repeted-mesures ANOVA (SPSS 18.0 for Windows). Significnce ws ccepted when p Cohen s d effect sizes (ES < 0.5, smll; , moderte; 0.8, strong) were lso clculted to exmine performnce trends (Cohen, 1988). Further nlysis identified the smllest worthwhile chnge (SWC) in performnce/physiologicl mesures between SP nd PL time trils using the method outlined by Btterhm nd Hopkins (2005). The SWC ws set t Cohen s unit of 0.2, representing the hypotheticl, smllest chnge in mesures tht would benefit the thlete. Where the chnces of benefit or hrm were both clculted to be > 5%, the true effect ws deemed uncler. When cler interprettion ws definitively possible, qulittive descriptor ws ssigned to the following quntittive chnces of benefit: 25-75%, benefit possible; 76-95%, benefit likely; 96-99%, benefit very likely; > 99%, benefit lmost certin (Btterhm nd Hopkins, 2005). Results 100 kj (23.9 Kcl) time tril performnce There were no significnt differences (p > 0.05), moderte or lrge effect sizes or likely (or better) SWC vlues found for time to completion or men power output within nd between SP nd PL trils (Tble 1). There ws lso no difference in hert rte, RPE nd blood lctte vlues within or between ny trils. Oxygen uptke ws lso similr between trils, lthough first minute VO 2 Tble 1. Men (±SD) 100 kj (23.9 Kcl) cycling time tril results for supplementtion with sodium phosphte (SP) or plcebo (PL) 1 nd 8 dys post-loding (n = 10). 100 kj (23.9 Kcl) SP Dy 1 SP Dy 8 PL Dy 1 PL Dy 8 Time to Completion (s) (34.6) (33.3) (35.9) (38.1) Averge Power (W) 479 (85) 482 (75) 473 (79) 492 (87) Hert Rte post (bpm) 178 (10) 177 (7) 175 (7) 175 (8) Rting of Perceived Exertion 18 (2) 18 (2) 18 (2) 18 (2) Blood Lctte Post (mmol L -1 ) 9.1 (1.2) 9.3 (2.8) 9.0 (2.0) 9.4 (2.4) Pek VO 2 (Oxygen uptke; L min -1 ) 5.08 (.39) 5.21 (.37) 5.03 (.35) 5.12 (.31) 1st min VO 2 (L min -1 ) Ave VO 2 (L min -1 ) 2.95 (.37) (d =.47; 82/15/3 SWC) 3.75 (.22) (d =.84; 90/8/3 SWC) 3.14 (.43) 2.88 (.33) 3.94 (.23) 3.74 (.18) 1st min V E (Ventiltion expired; L) 82.5 (21.8) 82.5 (13.8) 80.3 (15.7) 2.86 (.50) (d = 0.60; 88/10/2 SWC) 3.77 (.21) (d = 0.77; 93/6/1 SWC) 76.3 (18.9) (d = 0.37; 80/18/2 SWC) Ave V E (L) (15.6) (10.4) (10.7) (15.8) = compred with SP8: d = effect size, SWC = smllest worthwhile chnge probbility.

4 532 Sodium phosphte, VO 2 nd cycling Tble 2. Men (± SD) 250 kj (59.7 Kcl) cycling time tril results for supplementtion with sodium phosphte (SP) or plcebo (PL) 1 nd 8 dys post-loding (n = 9). 250 kj (59.7 Kcl) SP Dy 1 SP Dy 8 PL Dy 1 PL Dy 8 Time to Completion (s) (112.7) (104.2) (95.1) (117.8) Averge Power (W) 379 (57) 386 (58) 377 (47) 380 (63) Hert Rte post (bpm) 180 (16) 179 (14) 180 (14) 180 (13) Rting of Perceived Exertion 18 (1) 18 (1) 18 (1) 19 (1) Blood Lctte Post (mmol L -1 ) 9.2 (4.2) 9.1 (4.4) 9.2 (3.1) 8.3 (2.8) Pek VO 2 (Oxygen uptke; L min -1 ) 5.18 (.82) 5.06 (.85) 5.21 (.66) 5.14 (.78) 1st min VO 2 (L min -1 ) 2.54 (.54) 2.54 (.51) 2.53 (.41) 2.42 (.40) Ave VO 2 (L min -1 ) 4.37 (.63) 4.45 (.60) 4.46 (.51) 4.41 (.60) 1st min V E (Ventiltion expired; L) 68.9 (22.3) 67.7 (18.7) 67.8 (21.9) 68.1 (17.5) Ave V E (L) (35.3) (27.3) (25.0) (27.1) Note: No significnt differences, moderte or lrger effect sizes nd likely or better smllest worthwhile effects were found. tended to be higher in SP8 compred with both SP1 (p = 0.150) nd PL8 (p = 0.105), s ws men VO 2 (SP1: p = nd PL8: p = 0.052). Furthermore, first minute V E ws higher for SP8 compred with PL8 (p = 0.140). Of note, the VO 2pek chieved during the time trils were 96.0 % (SP1), 98.5 % (SP8), 95.1 % (PL1) nd 96.8 % (PL8) compred with the VO 2pek chieved during the incrementl exercise test. 250 kj (59.7 Kcl) time tril performnce There were no significnt differences (p > 0.05), moderte or lrge effect sizes or likely (or better) SWC vlues for time to completion or men power output within nd between SP nd PL trils (Tble 2), despite fster (~13 s) men completion time nd slightly higher (~2%) verge power output in SP8. Hert rte, RPE, blood lctte nd VO 2 responses to exercise were lso similr between trils (p > 0.05). The VO 2pek chieved during the time trils were 96 % (SP1; men time = s; men power = 379 W), 94 % (SP8; men time = s; men power = 386 W), 97 % (PL1; men time = s; men power = 377 W) nd 96 % (PL8; men time = s; men power = 380 W) compred with the VO 2pek chieved during the incrementl exercise test. Serum phosphte There were no differences (p > 0.05) in serum phosphte levels recorded with supplementtion for either the 100 kj (23.9 Kcl) (men ± SD: bseline 1.27 ± 0.18; SP ± 0.17; SP ± 0.12; PL ± 0.12; PL ± 0.18 mmol l -1 ) or 250 kj (59.7 Kcl) trils (men ± SD: bseline 1.23 ± 0.17; SP ± 0.13; SP ± 0.08; PL ± 0.15; PL ± 0.18 mmol l -1 ). Discussion This is the first study to ssess the effects of SP supplementtion on shorter durtion, higher intensity (100 kj/ 23.9 Kcl, ~3-4 min; nd 250 kj/ 59.7 Kcl, ~10-12 min) exercise performnce. In ddition, it is the first study to exmine exercise performnce both 1 nd 8 dys post supplementtion, to determine whether ny effect of SP loding persists cross this time frme. Results showed tht SP supplementtion hd no significnt effect on either 100 kj/ 23.9 Kcl or 250 kj/ 59.7 Kcl cycling time tril performnce on either dy 1 or 8 fter loding. In ddition, no effect on hert rte, RPE nd blood lctte response to exercise ws noted. Further, oxygen consumption ws lso similr between trils nd dys, lthough moderte effect sizes nd SWC vlues indicted tht first minute nd men VO 2 during the 100 kj/ 23.9 Kcl time tril tended to be higher in SP8 compred with both SP1 nd PL8, with this reflected, in prt, by higher first minute men V E. Results from some previous studies hve shown benefits to endurnce performnce following supplementtion with similr mounts of SP s used here. Specificlly, Kreider et l. (1992) nd Follnd et l. (2008) hve reported significntly fster 40 km (by ~8%, 3.5 min) nd 16.1 km (~3 %, s) cycling time tril performnces respectively. We lso recently found (NS) decresed time to completion of ~60-70 s (~ 2% fster) over 1000 kj/ Kcl (~40 km) cycling time tril (Brewer et l., 2013). In the present study, 250 kj/ 59.7 Kcl time tril performnce ws lso ~ 13 s (~2%) fster in SP8, but this result ws lso NS nd not ssocited with ny moderte (or better) effect sizes or likely (or better) smllest worthwhile (beneficil) chnge vlues. Collectively, these results suggest tht the exercise durtion is n importnt fctor with regrd to potentil ergogenic benefits of SP supplementtion. Here, the time trils used took ~3-4 min (100 kj/ 23.9 Kcl) nd ~10-12 min (250 kj/ 59.7 Kcl) to complete, compred with ~26 to ~55 min in studies demonstrting n ergogenic effect (Follnd et l., 2008; Kreider et l., 1992). Specificlly, the shorter durtion nd higher intensity endurnce exercise protocols used here my not hve llowed the potentil erobic benefits ssocited with SP loding (principlly, greter unloding of oxygen due to incresed 2, 3 DPG levels, enhnced myocrdil efficiency nd greter vilbility of phosphte for oxidtive phosphoryltion) to hve ny pronounced effect (Chsiotis, 1983; Czub et l., 2008; Kreider et l., 1990; 1992). Possibly, the potentil erobic exercise benefits from SP supplementtion (1-8 dys lter) my hve greter ergogenic role in longer durtion (~25 min +), lower intensity distnce efforts, where the percentge totl erobic energy contribution is greter, rther thn shorter (< 15 min), more intense, exercise tsks. The potentil improvements in buffering cpcity from SP supplementtion my lso hve limited effects unless there re mjor disruptions to norml cidbse homeostsis. Here, lthough ph vlues were not tken, the indirect evidence of lctte ccumultion being only ~ 9 to 10 mmol L -1 fter the time trils my suggest tht only moderte chllenge to cid-bse blnce ws presented by the exercise chllenges.

5 Brewer et l. 533 In reltion to the potentil mechnisms of ergogenic effect with SP supplementtion, this study found no difference in serum phosphte levels post-loding between trils. Notbly, review by Trembly et l. (1994) emphsised the need for mesurble chnge in serum phosphte post-loding s evidence for n intervention effect to hve occurred. While this hs been reported in some studies (Czub et l., 2009; Kreider et l., 1992), others hve found improved erobic cpcity nd exercise performnce with no chnge between pre nd postloding resting serum phosphte levels (Brewer et l., 2013; Stewrt et l., 1990), suggesting tht this mesure my be inconsequentil for ny physiologicl nd/or performnce chnges. The mesurement of 2, 3 DPG levels before nd fter SP loding (unfortuntely unvilble for this study) my be more compelling from mechnistic stndpoint thn serum phosphte vlues, which hve wide rnge of pre loding levels (suggesting lrge individul vrition) reported in the literture (~ 0.8 to 1.4 mmol L -1 : Czub et l., 2008; Kreider et l., 1990; 1992). Interestingly, lthough no effect of SP supplementtion on exercise performnce ws noted in the present study, first minute nd men VO 2 in the 100 kj (23.9 Kcl) time tril tended to be higher in SP8 (3.14 L min -1 ; 3.94 L min -1 respectively) compred with both SP1 (2.95 L min -1 ; 3.75 L min -1 ) nd PL8 (2.86 L min -1 ; 3.77 L min - 1 ) (bsed on moderte effect sizes nd SWC vlues). Few SP loding studies hve mesured VO 2 during the ctul performnce test, but Kreider et l. (1992) reported n incresed men VO 2 (from 80 to 86% VO 2 mx; from 4.13 to 4.82 L min -1 ) nd ventiltion (125.1 to L min -1 ) throughout 40 km cycling time-tril nd time to nerobic threshold (14.86 to min) during n incrementl exercise test. A 17% (220 to 257 W) greter men power output ws lso recorded, in conjunction with significntly fster time tril performnce (45.75 to min). Follnd et l. (2008) hve lso reported tendency (p = 0.07) for n increse in VO 2pek fter SP supplementtion during 16.1 km time tril, in which men power output ws lso ~ 10% greter nd completion time ~ 3% fster. Similrly, in our study, men VO 2 for SP8 ws ~76 %VO 2pek compred with ~74 %VO 2pek in SP1 nd PL8 in the 100 kj/ 23.9 Kcl time tril. However, no other physiologicl or performnce chnges were seen in SP8, such tht the incresed VO 2 cnnot be considered s beneficil, prticulrly s no greter men power output ws evident. Most SP loding studies hve mesured VO 2 mx in seprte incrementl (rther thn performnce) test, with improvements reported both immeditely fter supplementtion (Kreider et l., 1992) nd over the next three weeks with continued lower doses (Czub et l., 2009). Similrly, Brewer et l. (2013) found n incresed VO 2pek with SP loding, initilly by ~ 4%, which then incresed to ~8 % fter second loding phse either 15 or 35 dys lter. Our rtionle for mesuring VO 2 during the time trils ws to obtin simple indiction of whether oxygen kinetics were ltered by SP loding. Theoreticlly, SP supplementtion could potentilly fcilitte fster oxygen kinetics, vi the lowering of oxygen ffinity cused by incresed 2, 3 DPG levels (Cde et l., 1984; Chnutin nd Curnish, 1967; Kreider et l., 1992). Although the 100 kj/ 23.9 Kcl time-tril here showed greter first minute VO 2 in SP8 compred with SP1 (likely SWC) nd PL8 (medium ES nd likely SWC), this ws not similrly mtched by higher men power output or fster time to completion, therefore no prticulr focus should be plced on this result. Lck of ssocition between chnges in VO 2 found in the current study nd improved exercise performnce my be due to the reltively greter nerobic energy contribution required in the short-term, higherintensity 100 kj/ 23.9 Kcl effort used here in comprison to previous studies using longer durtion exercise tsks (Follnd et l., 2008; Kreider et l., 1992). Nevertheless, further reserch into SP supplementtion should continue to explore ny potentil effects on oxygen kinetics, s well s erobic cpcity. Conclusion In conclusion, six dys of SP supplementtion did not ffect shorter durtion (<15 min) cycling time tril performnce, either 1 or 8 dys fter loding. While oxygen kinetics (first minute nd verge VO 2 ) were slightly greter on dy 8 in the 100 kj (23.9 Kcl) time tril, the bsence of ny effect on men power output or completion time suggests tht no prticulr physiologicl significnce should be scribed to this result. Future studies should investigte the effect of SP loding on repeted sprints nd simulted rod rce performnce over extended durtions (>30 min), where SP my be likely to hve more beneficil effect (Brewer et l., 2013; Follnd et l., 2008; Kreider et l., 1992). Acknowledgment The uthors cknowledge the ssistnce of PthWest Lbortory Medicine, Royl Perth Hospitl, Perth, Austrli for the nlysis of serum phosphte. References Avioli, L. (1988) Clcium nd phosphorus. In: Modern nutrition in helth nd disese. Eds: M. Shils & V. Young. Phildelphi: Le & Febiger Btterhm, A.M. nd Hopkins, W.G. (2005) Mking meningful inferences bout mgnitudes. Sportscience 9, Borg, G. (1982) Psychophysicl bses of perceived exertion. 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6 534 Sodium phosphte, VO 2 nd cycling Czub, M., Zjc, A., Poprzecki, S., & Cholew, J. (2008). The influence of sodium phosphte supplementtion on VO 2 mx, serum 2, 3 diphosphoglycerte level nd hert rte in off-rod cyclists. Journl of Humn Kinetics 19, Czub, M., Zjc, A., Poprzecki, S., Cholew, J. nd Wosk, S. (2009) Effect of sodium phosphte loding on erobic power nd cpcity in off rod cyclists. Journl of Sports Science nd Medicine 8, Frber, M., Crlone, S., Plnge, P., Serr, P., Poletti, V. nd Fineberg, N. (1987) Effect of inorgnic phosphte in hypoxemic chronic obstructive lung disese ptients during exercise. Chest 92(2), Follnd, J.P., Stern, R. nd Brickley, G. (2008) Sodium phosphte loding improves lbortory cycling time-tril performnce in trined cyclists. Journl of Science nd Medicine in Sport 11, Kreider, R.B., Miller, G.W., Willims, M.H., Somm, C.T. nd Nsser, T.A. (1990) Effect of phosphte loding on oxygen uptke, ventiltory nerobic threshold nd run performnce. Medicine nd Science in Sports nd Exercise 22(2), Kreider, R.B., Miller, G.W., Schenck, D., Cortes, C.W., Miriel, V., Somm, C. T., Rowlnd, P., Turner, C. nd Hill, D. (1992) Effects of phosphte loding on metbolic nd myocrdil responses to mximl nd endurnce exercise. Interntionl Journl of Sports Nutrition 2(1), Lichtmn, M.A., Miller, D.R., Cohen, J. nd Wterhouse, C. (1971) Reduced red cell glycolysis, 2, 3 diphosphoglycerte nd denosine triphosphte concentrtion nd incresed hemoglobinoxygen ffinity cused by hypophosphtemi. Annls of Internl Medicine 74, Peeling, P.D., Bishop, D.J. nd Lnders, G.J. (2005) Effect of swimming intensity on subsequent cycling nd overll trithlon performnce. British Journl of Sports Medicine 39, Stewrt, I., McNughton, L., Dvies, P. nd Tristm, S. (1990) Phosphte loding nd the effects on VO 2 mx in trined cyclists. Reserch Qurterly for Exercise nd Sport 61(1), Stryer, L. (1988) Biochemistry. 3rd Edition. W.H. Freemn nd Compny, New York: [i]-xxxii, [1] Thompson, D.L., Grnthm, S., Hll, M., Johnson, J., McDniel, J., Servedio, F., Thompson, W.C. nd Thompson, W.R. (1990) Effects of phosphte loding on erythrocyte 2, 3diphosphoglycerte, denosine 5' triphosphte, hemoglobin nd mximl oxygen consumption. Medicine nd Science in Sport nd Exercise 22, S36. Trembly, M.S., Gllowy, S.D. nd Sexsmith, J.R. (1994) Ergogenic effects of phosphte loding: physiologicl fct or methodologicl fiction? Cndin Journl of Applied Physiology 19(1), Wllce, M.B., Crdinle, M., Lim, Y.S., Cmeron, N.J., Willimson, G. nd Choi, Y.U. (1997) Effects of short-term cretine nd sodium phosphte supplementtion on body composition, performnce nd blood chemistry. Coching nd Sport Science Journl 2(4), West, J.S., Ayton, T., Wllmn, K.E. nd Guelfi, K.J. (2012) The effect of 6 dys of sodium phosphte supplementtion on ppetite, energy intke, nd erobic cpcity in trined men nd women. Interntionl Journl of Sport Nutrition nd Exercise Metbolism 22(6), Key points Studies investigting the effects of sodium phosphte loding on shorter durtion (<15 min) nd higher intensity exercise performnce re lcking, s is reserch on how long ny ergogenic effect my lst. Loding did not improve cycling time tril (~3-4 min nd min) performnce either 1 or 8 dys fter supplementtion. Future studies should investigte the effect of sodium phosphte loding on repeted sprints nd simulted cycling rod rce performnce over extended durtions (>30 min), where it my be likely to hve more beneficil effect. AUTHORS BIOGRAPHY Cmeron BREWER Cmeron Brewer is Ph.D cndidte t the University of Western Austrli. Degree BSc Reserch interests Exercise physiology nd biochemistry. E-mil: cmeronbrewer1@gmil.com Brin DAWSON Professor of sport nd exercise physiology t the University of Western Austrli Degree PhD Reserch interests The physiology of intermittent high intensity exercise in the footbll codes nd other tem sports. E-mil: brin.dwson@uw.edu.u Kren WALLMAN Prof. A lecturer in exercise physiology t the University of Western Austrli Degree PhD Reserch interests Ergogenic ids, recovery modlities nd exercise in chronic illnesses. E-mil: kren.wllmn@uw.edu.u Kym GUELFI Assoc. Prof. t the School of Sport Science, Exercise nd Helth t The University of Western Austrli Degree PhD E-mil: kym.guelfi@uw.edu.u Cmeron Brewer School of Sport Science, Exercise nd Helth, M408, The University of Western Austrli, 35 Stirling Highwy, Crwley WA, 6009, Austrli