N=1 Series Part 9 90min Zone 2 rides with different inputs

Introduction

This is part 9 of 10 of the N=1 series of becoming a stronger cyclist for less than a cup of coffee a day. In this series I am going to take you through my journey from my local Masters C to Masters A in the space of 18 months, at the age of 57.

If you are reading this series for the first time, you can go back and read

Part 1, started with a daily smoothie and Creatine.

Part 2, incorporated sprint training into a weekly Zone 2 ride

Part 3, introduced strength training

Part 4, started taking sodium bicarbonate before races and strong group rides

Part 5, adopted a periodised and masters training plan

Part 6, completed Lactate Threshold and VO2 Max Testing

Part 7, increased Carbohydrate intake in races to 130g/hr

This time around, I became the guinea pig of my own little piece of citizen science, with a n=1 experiment. Initially I planned to ride the same 90 minute sustained endurance workout over 6 weeks with three different inputs. 1. Water, smoothie and creatine 2. Water, double shot espresso and creatine 3. Water and creatine. The purpose of the experiement was driven out of my curiosity to see which one of these pre-ride inputs would give me the lowest heart rate.

To drive some engagement in the experiment amongst my cycling colleagues and family members, I posted what I was doing and sought their comments on Strava as to which input would ellicit a lower heart rate. You can read those in the Appendix below, but to summarise most commenters believed the smoothie protocol would yield the lowest HR and I was inclined to agree with them. The reasons include: familiarity to the body, presence of carbs and nitrates, natural and easily digestible ingredients, and sustained energy release. One colleague commented that a statistically relevant determinant of HR is actually tiredness/freshness. HR being generally lower if you are tired. So keeping that variable static will be quite difficult unless your sleep/workouts throughout the week remain the same.

The feedback from my academic colleagues really sought to raise the bar on my humble experiment. Increase number of trials ✅ Calibrate Trainer ✅ Same time of day ✅ record air temp ✅ record time of drinking to be consistent ✅ After reading the responses, I was almost at the point that I was sorry I asked! I did everything except calibrate the trainer and record the air temp. Increased the number of trials to 9: Adhered to starting at approximately 5:45am on the same day of the week (except week1): Adhered to eating a moderately sized meal by my standards and not eating after 8pm the night before: Adhered to the same routine of pre-ride drink consumption time (20-30min pre-ride). With the air temp, I used a fan to be comfortable, but not cold.

Secondary to this experiment, was the factor of fasted training, something I had not done since starting the original n=1 experiment back in July 2024, consuming 20-30g of preride carbs in a smoothie each morning. Here's what the science says about the Energy Efficiency: Fat vs Carbohydrate

• Carbohydrate oxidation yields about 5.0 kcal per litre of oxygen consumed.
• Fat oxidation yields about 4.7 kcal per litre of oxygen consumed.
• This means the body must consume ~6–7% more oxygen to extract the same amount of energy from fat compared to carbs.

9.5 Hours of fasting is not a lot and the body stores glycogen in the liver (80-100 grams)and muscles (300 -500 grams) to ensure that blood glucose stays relatively constant when we are sleeping and not eating.

The Workout

source: TrainerRoad

Brasstown is 90 minutes of aerobic Endurance riding spent between 65-75% FTP.

Goals: Aerobic Endurance workouts are aimed at improving your aerobic (oxygen-reliant) power producing capabilities in a low-stress manner.

By riding for increasingly longer periods of time, your endurance muscle fibers become more efficient at utilizing oxygen as well as sparing sugar stores for more intense efforts.

The inputs

• Weeks 1,4,7: 300ml of warm water, Smoothie with Beetroot, Apple, Ginger & Celery (30g carbs) and 3g of creatine (my daily routine for the past year)
• Weeks 2,5,8: 300ml of warm water, Double shot of black coffee and 3g of creatine
• Weeks 3,6,9: 600ml of warm water and 3g of creatine

During each ride I consumed 800ml of water at minutes: 15: 30: 45: 60: 70: 80, which is when the bottle was emptied.

Data Capture
Record RPE (TrainerRoad) and observe the data from Strava, TrainerRoad and Garmin. 

Hypothesis of Fasted riding
Doing 90-minute Zone 2 rides in a fasted state can offer some intriguing physiological benefits—especially if you're aiming to improve metabolic efficiency and endurance. Here's what you might gain:

🚴‍♂️ Key Fitness Benefits

1. Enhanced Fat Oxidation
   Training in a fasted state encourages your body to rely more on fat as a fuel source, which can improve your ability to burn fat during longer rides.

2. Increased Mitochondrial Density
   Fasted Zone 2 rides may stimulate adaptations at the cellular level, such as increasing the number and efficiency of mitochondria—the energy powerhouses of your cells.

3. Improved Metabolic Flexibility
   Over time, your body becomes better at switching between fuel sources (fat and carbohydrates), which is especially useful for endurance athletes.

4. Aerobic Base Building
   Zone 2 training itself is excellent for building your aerobic engine. Doing it fasted may slightly amplify the endurance adaptations by stressing the system in a different way.

5. Potential Body Composition Benefits
   While not a magic bullet for weight loss, fasted rides can contribute to a caloric deficit and improved fat metabolism, which may help with body composition goals.

⚠️ A Few Caveats

• Performance Trade-offs: You might not hit the same power numbers or feel as strong during fasted rides, especially if you're doing them frequently.
• Not for Everyone: If you're new to cycling or have specific health conditions, fasted training might not be ideal.
• Timing Matters: Doing these rides too often or too intensely can lead to fatigue or under-recovery.

If you're using fasted Zone 2 rides as a tool—rather than a daily ritual—they can be a smart addition to your training mix. 

 👤 Individual Focus

This was an N=1 self-experiment tailored around my training load, goals, and schedule. I ride 6 times a week and race recreationally in criteriums, road races and fondos. I wanted to see which input would give me a lower heart rate.

 🎯 Control and Measurement

To create consistency:

- Environment: Same bike, indoor trainer, workout, day of the week and time of day.

- Tracking tools:

  - Power meter, cadence meter and heart rate monitor for objective metrics

  - Strava Relative Effort (RE) score is an analysis of your heart rate data. By tracking your heart rate through your workout and its level relative to your maximum heart rate, Strava attaches a value to show exactly how hard you worked.

  - Track: 7 day average Heart rate variability (HRV), average heart rate during the ride, Training Stress Score from the previous week.

No major dietary changes were introduced during the test window to isolate training effects.

 📊 Data Analysis

source: Garmin Connect Plus & TrainerRoad

Taking a look at the raw data, it was the water input which provided the lowest average HR. 

• Smoothie Avg HR 128 BPM (from 3 rides)
• Caffeine Avg HR 126 BPM (from 3 rides)
• Water Avg HR 124 BPM (from 3 rides)
• Average HR 126 (from 9 rides)
• Smoothie and caffeine both produced the highest Avg HR of 130
• Water produced the lowest Avg HR 120 BPM

source: Garmin Connect Plus

The graphed analysis of the data reveals that the lowest Avg HR (light blue) was recorded on days when my 7 day Avg HRV (orange) was lower, which suggests I was in a more fatigued state.

source: Garmin Connect Plus & TrainerRoad

Fatigue and a lower 7 day Avg HRV could be the result of many different inputs.  A bad night's sleep, eating too late in the day, alcohol consumption, work/life stressors (all of which I tried to avoid), high training load or a multitude of other factors. The graphed analysis with Training Stress Score from the previous week also sheds light on how much fatigue I might be bringing into the ride. For example, the first ride was only two days after finishing the 3 stage Bendigo Tour, where my average HR for the ride was 125, which was below the average and 7 day Avg HRV was 25, 2 below the average.

Of the three highest recorded Avg HRs (129, 130, 130), my 7 day Avg HRV for those results were above the average (27) for the trial, pointing to the body's rested state as being linked to a higher Avg. HR.

Of the three lowest recorded Avg HRs (124, 123, 120), my 7 day Avg HRV was lower than the average (27), pointing to the body's fatigued state as being a determinate of a lower Avg. HR.

Returning to my learned colleauges, one was right. Simon said the relevant determinant of HR is actually tiredness/freshness. HR being generally lower if you are tired.

Back to the science on the topic. When you're fatigued, your body’s ability to elevate heart rate is blunted due to reduced nervous system responsiveness, impaired muscular efficiency, and hormonal shifts that dampen cardiovascular output. 

Autonomic Nervous System Suppression
- Fatigue, especially from overtraining or sleep deprivation, shifts the balance toward parasympathetic dominance (rest-and-digest mode).
- This suppresses sympathetic activation, which is normally responsible for increasing heart rate during exercise.
- The result: blunted heart rate response, even when effort increases

 ⚠️ Limitations

While promising, the experiment had its limitations:

• Self-selected format: I controlled as many of the variables as I could within the boundaries of the experiement.
• External variables: Weather, mood, fatigue from other workouts may have influenced performance. 
• No control group: Couldn’t compare directly to the results of a wider sample size
• Any improvements in power records could have been the cumulative results of other training interventions

The Results

Power Records during the experiment

During the 9 week window of this experiment, I managed record power numbers from 40 - 116 seconds (back end of races) and from 56 - 64 minutes (intense 90min road race).

Cost

$0.00 No additional cost as I was already doing these things.

Conclusion

So was this just a waste of time to find something that I could have just looked up using AI?  Actually I did afer the experiment and the responses from CoPilot and Claude followed those of most of my colleauges and whilst they may have been technically right, they missed out on the fatigue factor.

source: CoPilot & Claude

By conducting this experiment, I have an achieveable benchmark endurance ride, which I can rely on to inform me of how my body is handling the current training load. I have also done 6 fasted workouts, which I would not have otherwise done, which are well known to have physiological benefits and may have contributed in some small way towards some record power numbers in race scenarios.

The data correlated lower HRV scores with lower average heart rates. Lower HRV scores can be a useful guide to the body's fatigue and readiness for training.

Journal Articles

Beneficial metabolic adaptations due to endurance exercise training in the fasted state

Exercise in the fasted state facilitates fibre type-specific intramyocellular lipid breakdown and stimulates glycogen resynthesis in humans

Marco Altini’s sub stack on HRV and low HR training 

Appendix - Comments on expected results from colleauges

Aaron

Caffeine = elevated HR
Vasodilator (nitrates) = lowered HR
Creatine is a fixed variable so no delta induced with its inclusion in all 3 protocols.

Simon

So I’m thinking that a statistically relevant determinant of HR is actually tiredness/freshness. HR being generally lower if you are tired. So keeping that variable static will be quite difficult unless your sleep/workouts throughout the week remain the same. Other than that agree with AK but will be interesting to see the results.

Nathan G

I would suggest your current daily routine, as the introduction of a caffeine as a stimulant is likely to elevate heart rate & water alone, once you are depleted of your stored energy will likely correspond with an elevation in heart rate.

Tim

I think your current regime (smoothie & creatine) will give lowest HR

Deane

I think week 1 & 4 will provide you with the lowest heart rate. I'm probably biased here, but I regularly drink beetroot juice ( for nitrate) & consume ginger helps my stomach when consuming a lot of gels & sugary fuel. Celery is refrshing too, so my theory is the foods your consuming are natural & may be easy to process, utilise & sustain efforts, therefore your body would be coping better which inturn ensures a lower heart rate. Obviously this is purely on my personal opinion & experiences consuming these foods. 

Luke

I reckon current regimen will deliver the goods. Your body is used the routine, there are other goodies in the smoothie from the vegetables/fruits, the creatine is excellent too.
Water & coffee - while rewarding would (I believe) not be likely to produce enduring results - possibly as brief as just the ride and likely to reinforce a plateau

Hamish (nephew)

This is really cool 🤩 my money’s on the smoothie. One thing I’m curious about is how much time you’re going to give for your inputs to digest? Would it even have an impact? Maybe less time to digest has higher sustain? 🤓

Dr James

Awesome citizen science! Repeats of the workouts with the same regime are technical (biological) replicates so you can validly still use them to calculate a treatment mean and variance that relates to you, but not the entire human population. So in your current design n=2, which is not enough to understand the variance around the mean. I suggest having 3-4 replicates of one treatment and can then calculate how many observations you will need to detect a meaningful difference. I think you would also need to make sure you do it at the same time of day at the same point in the week. Record air temp and HRV and you can use them as random effects or covariates in your analysis.

And most importantly of all - don’t forget to calibrate your trainer each time! They drift a lot, particularly if they start cold and warm up as you start using it. Get it to operating temperature first if you can.

Carl

The Beetroot Smoothie and it’s Nitrate content would by far out-weigh others as has less load on the heart keep cranking champ.

Lachlan (son)

My thoughts are that the smoothie will come out no.1 as the carbs and nitrates are a great fuel source for a 90 minute ride although a big factor that can effect the outcome of all the inputs is your diet the night before your ride eg. a carb heavy dinner such as pasta will give you a good base of stored glycogen. Following that the 600ml of water would be second for me as a double shot of coffee depending on your average caffeine intake could spike your heart rate significantly and although potentially giving a short burst of energy may burn you out and prevent you from finding consistency in your ride. 

Sebastian

I think in general fresh veg and fruit should keep HR lower as oposite to caffeine, so expect Weeks 2 and 5 return higher HR. Not sure about creatine but I suspect it should be neutral, as it plays role in muscle recovery rather that regulating cardiovascular system. This is my little contribution based on my limited training experience.

Aaron

As Lachlan mentions, and something I have read in all the physiology test studies I have read, they fix the food for 24 hours pre-test so the diet is the same each time, to alleviate carb load differences. They also deny caffeine etc but that's part of the test protocol so different in this case.