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Jem Arnold Profile picture
Jem Arnold
@jem_arnold
PhD candidate 🇨🇦 physiotherapist. Sport vascular conditions, performance testing, mNIRS. Treat declarative statements as questions?
Jul 29 • 12 tweets • 5 min read
Can mNIRS muscle oxygenation be used to estimate peripheral 🦵training load/stress?

Similar to using time >90% VO2max for central 🫀cardiovascular stress

A new paper provides some descriptive data for runners performing HIIT and SIT 1/12🧵 (study 🔗 in alt text👇) An example of the muscle deoxygenation responses for the 1 km (a) and 400 m (b) session. An ischemia/hyperaemia calibration was performed prior to each session to normalize the NIRS signals, whereby the deoxygenation signal was scaled from 0-100% corresponding to the minimum and maximum during the ischaemia and hyperaemia periods, respectively. Average deoxygenation was greater during 400m than in 1km intervals. Bellinger et al 2025. Maximizing Muscle Deoxygenation during Interval Training in Middle-Distance Runners. https://doi.org/10.1007/s00421-025-05903-1 In an exploratory study, @Phil_Bellinger et al compared 1km vs 400m running intervals with @Artinis_MS Portamon on gastroc (calf)

They found greater peripheral muscle deoxygenation in the shorter, higher speed session, and greater central stress in the longer distance session 2/ Time spent with values > 60% muscle deoxygenation and time spent with a heart rate > 90% peak heart rate throughout each session. a = Significantly different from 1 km session. 400m sprints had greater time >60% deoxygenation, while 1km intervals had greater time >90% HRmax. Possibly indicating greater peripheral and central stress, respectively. Bellinger et al 2025. Maximizing Muscle Deoxygenation during Interval Training in Middle-Distance Runners. https://doi.org/10.1007/s00421-025-05903-1
Feb 18 • 17 tweets • 6 min read
In our recent meta-analysis with trained athletes, did the athletes who improved their VO2max more also improve their endurance performance more?🤔

No! 😮
In this dataset, +1% change in VO2max was associated with only +0.04% change in TT performance. But why? 1/15🧵 A one-stage linear mixed effects model meta-analysis based on our individual participant dataset (but not peer reviewed) showing individual athlete percentage change scores for both VO2max (maximal oxygen uptake) and time-trial (TT) performance, for 236 trained athletes in 6 studies. The relationship (correlation) between change in VO2max and change in performance was not significant and not meaningful. The overall change in VO2max only explained around 25% of the total variance in the change in endurance performance, across athletes. This is the third thread about our recent meta on training intensity distribution (TID)

The last thread was about our secondary findings 👇. This one is about some interesting exploratory observations
🔗Links below, more details in the 📊Alt text 2/
Feb 10 • 13 tweets • 4 min read
In our recent meta-analysis we found:
🔴Higher level competitive athletes improved VO2max modestly more with Polarised training
🔷Lower level recreational athletes modestly more with Pyramidal training

This is what those differences looks like 👇
But is this meaningful? 🤔1/🧵 A density plot using {ggdist} showing distribution of individual observations for the change in VO2peak pre to post training intervention. For the full meta-analysis sample (bottom grey figure) the mean difference of 0.11 ml/kg/min was not significant between polarised vs pyramidal training intensity distribution (TID) models. For recreationally trained vs competitive athletes, the contrast was significant such that competitive athletes improved more following polarised training (top), and recreational athletes improved more following pyramidal training (middle). But the mean differences wi... This is the second thread about our recent meta on training intensity distribution (TID)

Start with the first thread 👇for main findings. Keep reading here for more of the story!
🔗Links below, and more detail on figures in the 📊Alt text 2/

Jan 31 • 21 tweets • 6 min read
Polarised🆚Pyramidal🆚Threshold

Which training model is best?🏆
It might matter how trained you are🤔

Our new meta-analysis tries to answer which training intervention produces the greatest improvements in endurance performance in trained athletes

Thread🧵 & 🔗links below👇 Article link:


Keep reading for a summary of our main findings and questions 📚🧵2/18

Alt text in images have additional details & links. Full access link at the bottom🔗👇 link.springer.com/article/10.100…Image of article title, authors, abstract, and key points. Key points reads: 1. When training load was quantified by time in heart rate zone, our results indicate that the adaptations to maximal oxygen uptake following different training intensity distribution (TID) interventions is dependent on performance level. Athletes at a more competitive level may benefit from a polarized (POL) TID intervention and recreational athletes from a pyramidal (PYR) TID intervention. 2. A pooled analysis using different methods to estimate borders between training zones among the included studies did not a...
Oct 21, 2024 • 12 tweets • 4 min read
Here's a strange new study discussing doping and cyclist's iliac syndrome (FLIA/endofibrosis). I don't think I can take it literally, but I will take it seriously

Can doping increase risks in endofibrosis? Likely yes
Is FLIA/endofibrosis caused by doping? No
Let's discuss💭🧵👇 Image Although not entirely clear, and entirely un-cited, this sentence speculates on the mechanisms relating PEDs to exacerbated pathological remodelling of the iliac artery. This more or less conforms to my understanding of the risks of PEDs on peripheral vascular health 2/ Image
Sep 19, 2024 • 17 tweets • 7 min read
Just published from my (eventual) PhD thesis 🔖

Review of conservative treatment (CTx) for Flow Limitations in the Iliac Arteries (FLIA, endofibrosis) and proposal of Return to Sport (RTS) guidelines after surgery

Here is what we learned🧵/14 Image Briefly, FLIA is an uncommon vascular condition where the iliac artery is compressed/kinked during exercise and performance is impaired by ischaemia & claudication. Often seen in cyclists in an aero racing position

Good background thread here 2/
Aug 15, 2024 • 16 tweets • 6 min read
Just published on #NIRS #muscleoxygenation Thanks to co-authors, reviewers, & editors

Muscle reoxygenation is slower after higher cycling intensity, and is faster and more reliable in locomotor than in accessory muscle sites

What is it all about? 🧵/12
frontiersin.org/journals/physi…
Image We know quite well how quadriceps (VL) responds with cycling intensity, but there are fewer data in other muscles

We want to know how multiple muscles respond simultaneously, to gain insight into how local responses are aggregated into systemic responses 2/ Image
Jul 5, 2024 • 11 tweets • 4 min read
A new review of flow limitations in the iliac arteries (FLIA) / endofibrosis 🩸🩸 in female athletes 🚴‍♀️ 🏃‍♀️

A quick summary and context 📚🧵👇 Image FLIA is a condition affecting endurance athletes where blood flow is limited by compression & kinking in the iliac arteries during exercise. The athlete is limited by gradually worsening pain & claudication in one or both legs

More background info here:
Jan 21, 2024 • 17 tweets • 6 min read
🩸Blood lactate [BLa] does NOT increase exponentially during high intensity exercise 🧑‍🔬

Why do we make this common mistake?

I think because we have focused too much on the lactate test

And forgotten what information that test is trying to give us about real exercise
🧵1/14 Image We are probably familiar with the🩸BLa curve during an incremental exercise test

As intensity increases 🩸BLa accumulates at a faster rate, approximating an exponential increase

We can estimate a 'threshold' in this curve, but what is this threshold telling us?
2/ Image
Dec 12, 2023 • 5 tweets • 2 min read
@SciTriat and I just chatted about training above or below threshold to improve V̇O₂max and performance, interpreting group-level research to individual-level application, and how much day-to-day variability to expect in common training metrics
scientifictriathlon.com/tts420/
Image We talked about a few threads I recently posted

The first was about our recent meta analysis on training above vs below the maximal metabolic steady state effects on V̇O₂max and TT performance outcomes with Dr. Michael Rosenblat & @StephenSeiler

Oct 26, 2023 • 4 tweets • 2 min read
Reading now. Hitting a lot of check marks on my training study wishlist 👏👏 @ingvillodden et al

The plot thickens on interval programming! Very well described methods. Definitely more papers to come from this dataset
Image iiiiiinteresting. That pesky dissociation between improvements to V̇O₂max and TT performance outcomes? 🤔🤔 Image
Sep 29, 2023 • 15 tweets • 5 min read
Significant correlation doesnt imply good individual prediction

If you have asked "Why cant my apps predict my response when they have so much data on everyone?"

Because lots of data improves *confidence intervals* but DOESNT improve *prediction intervals*

Lets simulate! 🧵/14 Image There is always uncertainty in any measurement

We make estimates about training data by sampling from the population of athletes

We observe the sample to estimate the population

I'll simulate some power data representing threshold or TT performance and sample from it
2/ Image
Sep 22, 2023 • 14 tweets • 5 min read
Does training above max metabolic steady state MMSS (CP, FTP, MLSS, LT2) improve V̇O₂peak & time-trial in endurance-trained athletes MORE than training only below MMSS?

Think the answer is obvious? We kinda did too. So we did a meta-analysis! 📚🔖
🧵/13

link.springer.com/article/10.100… We looked at research comparing groups of trained runners, cyclists, or rowers performing:

1) exercise ONLY below MMSS (MICT, heavy, tempo, sweet spot..)

vs

2) exercise below AND above MMSS (HIIT, SIT, severe & extreme domains)

with V̇O₂peak, Wpeak, or TT outcomes
2/ Image
Jun 21, 2023 • 36 tweets • 20 min read
Critical Power (CP) is ⬇️ at 100 vs 60 rpm, and costs ⬆️V̇O2

But preferred cadence is typically 80-100 rpm 🤔

Does training at ⬇️or ⬆️cadence improve CP & V̇O2max more?

I find the physiology fascinating! Here’s some of what I'm learning🚴‍♀️🚴🚴‍♂️
1/🧵
pubmed.ncbi.nlm.nih.gov/25523595/ Image I recently said CP is ⬆️at ⬇️cadence because blood flow (BF) is ⬆️

That's not quite right

BF is ⬆️ per pedal cycle, but BF and O2 delivery are ⬇️per unit time

There must be another reason why CP is ⬆️at ⬇️cadence 🤷‍♂️
2/
Apr 23, 2023 • 15 tweets • 5 min read
Critical Oxygenation may estimate critical power with NIRS measured at the quadricep (RF) in a single-session multi-stage protocol

I wanted to test the method with our dataset of mixed fitness competitive F & M cyclists

It doesn't quite work for us. but why?🤔
🧵/14 21 competitive cyclists (cat 4 to national level) perform 5-1 tests with multi NIRS measures, including rectus femoris (RF) as per OP Matthews et al

As in this representative athlete, the RF profile is generally parabolic: ⬆️SmO2 at low workloads, ⬇️SmO2 at high workloads
2/ Image
Jan 9, 2023 • 4 tweets • 2 min read
Throwaway line in a thesis I'm reading got me thinking regarding adaptive effects of intermittent HIIT vs SIT vs continuous HIIT:

Is the *rate* of metabolic disruption important for adaptive signalling, independent from the magnitude of disruption? 🤔 ... The former presumably being greatest at work bout onset, the latter being greatest at end

SIT would presumably induce the greatest onset flux

Intermittent HIIT (eg 30x15s) a high volume of onset events

While the end magnitude may be similar across all (ie iso-effort) ?
Jan 7, 2023 • 5 tweets • 2 min read
Weekend project: simulated data based on observed NIRS recordings during 4x4-min cycling HIIT session in severe (SVR) domain with @MoxyMonitor

End-work SmO2 (last 60-sec mean of each bout) may ⬆️or⬇️ across the session related to caliper skinfold thickness (SF) at VL
1/🧵 ⬇️SmO2 across bouts in LOW SF group (red):

⬇️SF ⇒ more optical signal comes from metabolically active muscle tissue, where ⬆️VO2 during SVR as ⬆️[metabolite] (contributes to ⬆️VO2 slow component)

Hence ⬆️⬆️O2 extraction relative to ⬆️O2 delivery ⇒ ⬇️SmO2 in deeper tissues
Dec 8, 2022 • 7 tweets • 3 min read
Michael Rosenblat recently meta-analysed the effects of HIIT vs SIT for improving ⬆️VO2peak and ⬆️cycling TT performance

HIIT & SIT were similarly effective at improving VO2peak

BUT via different mechanisms
AND with different results to performance

researchgate.net/profile/Michae…
1/🧵 HIIT was subgrouped as short (<2min) med (2-4min) and long (>4min)

There were no significant differences between HIIT or SIT on improving VO2peak
2/7
Nov 4, 2022 • 6 tweets • 4 min read
Oh great question. I can't recall any literature specifically on NIRS & multi-muscle placement with bike fit, but I'd love to see that!

A few papers come to mind:
1/6 Saito et al 2018 performed incremental tests in aero & upright. They found no differences in duration or Wpeak between positions, but observed lower saturation (TOI) in VL & RF in aero. They suggest this could reflect greater musc O2 uptake in aero 2/6
pubmed.ncbi.nlm.nih.gov/30125046/
Oct 29, 2022 • 17 tweets • 12 min read
An overly-long and still non-comprehensive reading list for understanding #NIRS #muscleoxygenation in sport science! 🧵

1/15
Start with this concise opinion piece from Perrey on the emerging promise and future direction of NIRS research & application
pubmed.ncbi.nlm.nih.gov/35321522/ 2/15
Perrey & Ferrari's review on NIRS in the context of sport science gives background and is a great jumping off point for NIRS studies in your particular sport of interest
pubmed.ncbi.nlm.nih.gov/29177977/
Aug 9, 2022 • 5 tweets • 2 min read
The 'Incremental RPE Step Test' is a fun and useful experiment to perform with athletes

Used to cue athletes to pay attention to sensations across intensity spectrum

These are some typical responses I've noticed

Have you used something similar? Image We often set off too hard and overestimate power at low intensity

MOD domain or 'aerobic' zone is large! Not everything has to be right up at the top of it

'easy' ≠ 'good hard'

Sensations I cue include:
• light legs
• glass cranks
• nose breathing
• loose shoulders Image