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Sam Holness' scorecard

London Marathon

Sunday 23rd April, 2023

Within recommended ranges

Just outside recommended ranges

Significantly outside recommended ranges

  • 51g

    Carb per hour
  • 0mg

    Sodium per hour
  • 169ml

    Fluid per hour
  • 0mg/L

    Relative sodium concentration
  • 0mg/kg

    Caffeine per bodyweight
  • How Sam hit those numbers

    500ml x PH 1500 (Tablet)
    300ml x PH 1000 (Tablet)
    1 x Bagel with Peanut Butter
    1 x Banana
    1 x PF 30 Energy Chews
    4 x PF 30 Energy Chews
    500ml x Plain water

    How Sam's hydration and fueling went...

      • Sam set a new Guiness World Record by becoming the first openly autistic triathlete to complete the IRONMAN World Championships in 2022 and recently completed the London Marathon as part of his training for the 2023 triathlon season
      • Having struggled with gastrointestinal issues in almost all of his previous endurance events, it was a huge step forward for Sam to run a personal best time of 2:57:53 whilst experiencing no stomach issues in London


      • Sam has previously struggled with a “sloshing” sensation in his stomach when drinking large amounts, so has found great benefit from preloading before the race to ensure he starts optimally hydrated. This has helped him reduce the reliance on fluids during a race up to three hours long
      • After finishing a 500ml (16oz) bottle of PH 1500 with his breakfast, Sam sipped on ~300ml (12oz) of PH 1000 in the last hour before the race start
      • During the race itself, Sam was very regimented with his hydration strategy and took a sip of water at every aid station. He also drank a mouthful before and after each of his PF 30 Chews, which he planned to take every 30 minutes
      • Sam didn’t take any electrolytes during the run, but thankfully he didn’t experience any negative side effects from this. This is likely due to Sam’s appropriate sodium preload and the modest temperatures during the race (~13℃ / 55℉)
      • Given Sam’s moderate sweat sodium concentration (he loses 491 milligrams of sodium per litre of sweat), if his sweat rate were to increase, his electrolyte losses may begin to impair his performance through avenues such as muscle cramps or reduced blood volume causing an increased heart rate
      • For this reason, in future races of this length and intensity, and certainly for longer races like Sam's next race at the 2023 IRONMAN 70.3 World Championships, he may want to take some Electrolyte Capsules with him to help offset his losses


    Quick Carb Calculator Recommendation


    carb 30 mins before


    carb per hour during
      • Sam has long-since suffered with gastrointestinal issues whilst exercising, and it’s a common symptom among other autistic athletes
      • Because of this, Sam has trialled numerous methods of getting fuel in which don’t upset his stomach, or at the very least reduce the magnitude of upset. This has involved countless hours of gut training during his track interval sessions and long runs, to simulate high stress on his stomach whilst processing carbohydrates
      • Sticking to mainly plain, simple carbohydrates the night before and the morning of the race, Sam managed to carb-load effectively, and begin the marathon with optimally full glycogen stores
      • Then within the last 20 minutes before the gun went off, Sam ate a pack of PF 30 Chews to peak his circulating blood glucose and initiate some glycogen sparing in the early stages of the race
      • For the first hour, his plan was to eat nothing at all, only taking a sip of water from every aid station. This is something Sam had practised in training, and thought it would help his pre-race anxiety settle down before he began trying to digest food
      • From the 60 minute mark he then began taking one pack of PF 30 Chews every half an hour to provide him with ~60g of carb per hour for the remainder of the race
      • This strategy brought his overall fuel average to ~51g per hour, which despite being slightly below the recommendations from our Fuel & Hydration Planner, is a dramatic improvement from previous races where he’s struggled to take anything
      • The overwhelming positive from this race was Sam’s perfect (10 out of 10) energy levels and he experienced no GI issues at all for the first time in a long distance race
      • Going forwards, Sam is going to continue increasing his carb intake during races, and reap the benefits associated with greater energy availability


      • London Marathon is an iconic event on it’s own, but this race for Sam will always be a special memory as he broke the three hour barrier, and completed his first marathon with no GI issues
      • To help Sam optimise his fuel and hydration strategy further, he may want to include some sodium and practice starting his fuel intake earlier in the race to help maintain more stable blood glucose levels

    Key info

    Sam Holness

    Sweat sodium concentration
    Sweat sodium classification
    Very Low
    * determined by a PH Advanced Sweat Test


    Overall Time

    Event information

    London Marathon
    London, England
    23rd April, 2023
    Total Distance
    42.2km / 26.2mi

    Race conditions

    Weather Conditions
    Min Temp
    10°C / 50°F
    Max Temp
    15°C / 59°F
    Avg Temp
    13°C / 55°F

    Athlete feedback

    Race Satisfaction
    Hydration rating
    I was quite thirsty after the finish
    Energy levels
    Toilet stops
    GI comfort
    I did have one quick toilet stop, but only because I didn't go before the race
    No cramping

    Sam's Thoughts

     The crowds were amazing and helped me run so much faster

    Sam's full stats

     Carbohydrate (g)Sodium (mg)Fluid (ml)Caffeine (mg)Relative sodium concentration (mg/L)
    Total intake150050000
    Per hour5101690

    Data Confidence







    There is an adequate level of accuracy in the data collected and the numbers reported. The athlete manages to recall what they ate and drank including most specifics (brands flavours quantities plausible estimations of volumes). However there are estimations made within the data which affect the overall confidence level in the data reported.

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