PMID- 29453741
OWN - NLM
STAT- MEDLINE
DCOM- 20181126
LR  - 20220321
IS  - 1179-2035 (Electronic)
IS  - 0112-1642 (Print)
IS  - 0112-1642 (Linking)
VI  - 48
IP  - 5
DP  - 2018 May
TI  - Fuel for the Work Required: A Theoretical Framework for Carbohydrate 
      Periodization and the Glycogen Threshold Hypothesis.
PG  - 1031-1048
LID - 10.1007/s40279-018-0867-7 [doi]
AB  - Deliberately training with reduced carbohydrate (CHO) availability to enhance 
      endurance-training-induced metabolic adaptations of skeletal muscle (i.e. the 
      'train low, compete high' paradigm) is a hot topic within sport nutrition. 
      Train-low studies involve periodically training (e.g., 30-50% of training 
      sessions) with reduced CHO availability, where train-low models include twice per 
      day training, fasted training, post-exercise CHO restriction and 'sleep low, 
      train low'. When compared with high CHO availability, data suggest that augmented 
      cell signalling (73% of 11 studies), gene expression (75% of 12 studies) and 
      training-induced increases in oxidative enzyme activity/protein content (78% of 9 
      studies) associated with 'train low' are especially apparent when training 
      sessions are commenced within a specific range of muscle glycogen concentrations. 
      Nonetheless, such muscle adaptations do not always translate to improved exercise 
      performance (e.g. 37 and 63% of 11 studies show improvements or no change, 
      respectively). Herein, we present our rationale for the glycogen threshold 
      hypothesis, a window of muscle glycogen concentrations that simultaneously 
      permits completion of required training workloads and activation of the molecular 
      machinery regulating training adaptations. We also present the 'fuel for the work 
      required' paradigm (representative of an amalgamation of train-low models) 
      whereby CHO availability is adjusted in accordance with the demands of the 
      upcoming training session(s). In order to strategically implement train-low 
      sessions, our challenge now is to quantify the glycogen cost of habitual training 
      sessions (so as to inform the attainment of any potential threshold) and ensure 
      absolute training intensity is not compromised, while also creating a metabolic 
      milieu conducive to facilitating the endurance phenotype.
FAU - Impey, Samuel G
AU  - Impey SG
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
FAU - Hearris, Mark A
AU  - Hearris MA
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
FAU - Hammond, Kelly M
AU  - Hammond KM
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
FAU - Bartlett, Jonathan D
AU  - Bartlett JD
AD  - Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, 
      Footscray Park, Ballarat Road, Melbourne, VIC, 8001, Australia.
FAU - Louis, Julien
AU  - Louis J
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
FAU - Close, Graeme L
AU  - Close GL
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK.
FAU - Morton, James P
AU  - Morton JP
AD  - Research Institute for Sport and Exercise Sciences, Liverpool John Moores 
      University, Tom Reilly Building, Byrom St Campus, Liverpool, L3 3AF, UK. 
      J.P.Morton@ljmu.ac.uk.
LA  - eng
PT  - Journal Article
PL  - New Zealand
TA  - Sports Med
JT  - Sports medicine (Auckland, N.Z.)
JID - 8412297
RN  - 0 (Dietary Carbohydrates)
RN  - 9005-79-2 (Glycogen)
SB  - IM
MH  - *Dietary Carbohydrates
MH  - Exercise/*physiology
MH  - Glycogen/*metabolism
MH  - Humans
MH  - Muscle, Skeletal/*metabolism
MH  - *Physical Endurance
MH  - Sports
PMC - PMC5889771
COIS- CONFLICT OF INTEREST: Samuel Impey, Mark Hearris, Kelly Hammond, Jonathan 
      Bartlett, Julien Louis, Graeme Close and James Morton declare that they have no 
      conflicts of interest. FUNDING: No sources of funding were used to assist in the 
      preparation of this manuscript.
EDAT- 2018/02/18 06:00
MHDA- 2018/11/27 06:00
PMCR- 2018/02/16
CRDT- 2018/02/18 06:00
PHST- 2018/02/18 06:00 [pubmed]
PHST- 2018/11/27 06:00 [medline]
PHST- 2018/02/18 06:00 [entrez]
PHST- 2018/02/16 00:00 [pmc-release]
AID - 10.1007/s40279-018-0867-7 [pii]
AID - 867 [pii]
AID - 10.1007/s40279-018-0867-7 [doi]
PST - ppublish
SO  - Sports Med. 2018 May;48(5):1031-1048. doi: 10.1007/s40279-018-0867-7.