Jem Arnold
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jemarnold.bsky.social
Jem Arnold
@jemarnold.bsky.social
630 followers 360 following 350 posts
PhD candidate & physiotherapist | 🩸Iliac artery endofibrosis / FLIA | Endurance testing & NIRS.
Treat declarative statements as questions?
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jemarnold.bsky.social
Jem Arnold @jemarnold.bsky.social · Nov 14
Recently 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
(full PDF link at end of thread)
Conservative Management and Postoperative Return to Sport in Endurance Athletes with Flow Limitations in the Iliac Arteries: A Scoping Review - Sports Medicine
Background Flow limitations in the iliac arteries (FLIA) is a sport-related vascular condition increasingly recognised as an occupational risk for professional cyclists and other endurance athletes. S...
link.springer.com
jemarnold.bsky.social
Also realised the 300 hr project didn't include data collection at all. It was a secondary manuscript with an existing dataset. And the 400 hrs project was a systematic review. So no wonder my current data collection is already exceeding that 😬
captain7bag.bsky.social Cap @captain7bag.bsky.social · 1d
Thanks. Research has always something I’ve squeezed in on the side so I’ve never tracked hours but know it’s a lot. I think your hours are consistent with some other estimates I’ve gotten back.
February 5, 2026 at 3:11 PM
jemarnold.bsky.social
Good article I was able to contribute to, covering the good, the bad, and the unknown of endofibrosis in professional cyclists

But don't worry, despite the hyperbolic title, endofibrosis is not "coming for you and your little dog too" 😂
velo-velo-velo.bsky.social VELO @velo-velo-velo.bsky.social · 1d
All you need to know about Iliac artery flow limitation and endofibrosis, the mysterious and misdiagnosed scourge of elite cycling. bit.ly/4af6JiL
February 5, 2026 at 2:55 PM
jemarnold.bsky.social
I don't want to know but I really would like to know 🫣

#academia #academicchatter #AcademicSky #datascience
captain7bag.bsky.social Cap @captain7bag.bsky.social · 2d
How many hours of work typically go into publishing a sports med/phys research paper start to finish? @drphilipskiba.bsky.social @peter-leo.bsky.social @jemarnold.bsky.social @james-spragg.bsky.social (please share with whoever you else is on here)
February 4, 2026 at 3:42 PM
jemarnold.bsky.social
Other good threads have already talked about Kristian Blummenfelt’s implausible VO2peak of 101 ml/kg/min

Big if true.. big 'if'

It’s a great troll to get us #sportscience nerds arguing 😄 But we can ask some interesting questions!

Let me try to add some context with data! 🧵 #rstats #datavis
Metabolic cart data displayed briefly at the end of Kristian's test protocol, showing a VO2 value of 101.1 ml/kg/min (circled), and 7797 ml/min. VCO2 reads 7250 ml/min and RER is 0.93. Test time appears to be 1:14:15. No other data is legible on screen.
January 31, 2026 at 4:09 PM
Reposted by Jem Arnold
philipskotzke.bsky.social
Where should scientists communicate science today?

Recent discussions (IJSPP editorial; Ross Tucker on The Real Science of Sport) highlight the gap between the science we produce and the advice people receive.

What platforms do you think work best for science communication?

Let’s discuss 👇
January 25, 2026 at 1:23 PM
jemarnold.bsky.social
Wow! My colleague Dr. Martijn van Hooff just found a medical description of #endofibrosis in the iliac artery of a cyclist in the UK, published 1950!

Many of the same observed features and speculations on mechanisms, 35 years before the modern condition was described in Switzerland and France
image text extracted by LLM: Case 2 This patient, a man aged 23, gave no history of any definite traumatic incident, but explained that his hobby was sprint cycling. In August, 1944, after walking a distance estimated at... Histology.—The histological report on the excised segment of artery read as follows: “The artery is much decreased in size, and in consequence the internal and external elastic lamellae are tortuous and thickened. There is a slight increase in the amount of medial elastic tissue. The lumen is filled with fibrous tissue which has incorporated the intima. In this fibrous tissue are a few blood spaces which are lined by a simple epithelium. There is no evidence of any inflammatory reaction. There is nothing to suggest the cause for this now quiescent thrombosis” (Plate, Figs. 1, 2, and 3). A similar lesion or an intimal tear may be due to a “stretch-strain” or may be the result of traction on a muscular branch. The external iliac artery has been shown to be fixed to the ilio-psoas muscle at the level of Poupart’s ligament by the fusion of the iliac and transversalis fascia with the adventitia of the artery (Panton, 1923). The causes of the thrombosis in the above two cases would seem to be direct trauma in Case 1, who was struck by the falling tree, and indirect trauma due to stretch-strain from repeated flexion of the hip-joint in Case 2, the sprint cyclist. Prognosis In both cases, at the post-operative review, exercise caused the limb pulses to become palpably stronger, whereas pre-operatively the converse had been observed. Subjectively, both patients considered their condition to be much improved. The follow-up period cannot, however, be taken as sufficient for judgment of the long-term results.
January 22, 2026 at 3:53 PM
jemarnold.bsky.social
Yess Maggie!!! 💪💪
January 21, 2026 at 5:14 PM
jemarnold.bsky.social
Checked off the TODO list: create a repo to share and archive my future data vis projects

github.com/jemarnold/da...

With a lot of inspiration from #datavis and #rstats people

...but I already see a couple issues to fix.
✅one thing off, add ❎❎❎ more to do 😄
January 9, 2026 at 7:19 AM
jemarnold.bsky.social
Carb intakes are increasing among endurance athletes

But there is wide uncertainty in how much we actually expend, depending on absolute power output, relative intensity, and gross metabolic efficiency

Which factor has the biggest influence depends where we are on the map #rstats #datavis #cycling
Figure shows carbohydrate intake equivalent (grams per hour) as a function of power output (watts) from 100-400 W, for a range of isolines of RER (respiratory exchange ratio) from 0.7 to 1.00 (equivalent to the range of metabolic intensity). Each RER also has a band for gross metabolic efficiency (GE), which results in greater uncertainty for energetic output and therefore caloric and g/hr carb intake requirement. Figure titles: What is the plausible range of carbohydrate intake required to match 100% glycogen expenditure per hour? THIS IS NOT A RECOMMENDATION RER will be lowest at rest, somewhere in the middle in “zone 2”, and highest at and above FTP functional threshold power. Uncertainty ranges for GE derived from Ettema & Lorås, 2009. Efficiency in Cycling. A Review. https://www.researchgate.net/publication/24027428_Efficiency_in_cycling_A_review.
January 8, 2026 at 10:51 PM
jemarnold.bsky.social
Common question I hear: "My VO2max is x and my current threshold power is y. Is it possible for me to reach an FTP of z?”

It's surprisingly simple to predict power from VO2, and vice versa

We just need reasonable estimates for RER substrate oxidation and metabolic efficiency 📊🧵/4 #rstats #datavis
Figure visualising the percent of a VO2max of 5.0 L/min required to produce functional threshold power (FTP) between 300 and 400 W, with isolines for gross metabolic efficiency (GE, %) from 20-25% and RER at each GE value between 0.85-0.95. The question was “is it possible to achieve an FTP of 380 W at a VO2max of 5.0 L/min (71 ml/kg/min at 71kg bodyweight)?” Based on these calculations, that would require somewhere around 24% GE and ~90% VO2max, which is just about physiologically plausible for an elite male cyclist… but would certainly take some work to achieve.
January 8, 2026 at 10:11 PM
Reposted by Jem Arnold
adam-lg.bsky.social
@stephenjwild.bsky.social and others may get a kick out of this: Strava will display "weighted average power," which is
mean(f(Power)⁴)ᐧ²⁵, where f is an exponential decay. It seems to work! But I can't be alone in feeling it seems very "garden of forking paths-ish"
#statssky #bikesky
Strava Ride Statistics
If you ride with a power meter and a heart rate monitor, Strava’s premium subscription will display a number of summary statistics about your ride. These differ from the numbers provided by o…
science4performance.com
December 26, 2025 at 11:36 PM
jemarnold.bsky.social
{ggview} can print plots to Viewer (Rstudio or Positron) with true scaling. Adjust plot settings and see the final proportions immediately.

Save the plot once 👌

e.g.:
ggplot(...) +
ggview::canvas(width = 220, height = 220*2/3, units = "mm", dpi = 300)

per @nrennie.bsky.social #datavis #rstats
December 16, 2025 at 10:53 PM
jemarnold.bsky.social
Is it just me, or did {ggplot2} 4.0.0 S7 update break {camcorder}? 😢
#rstats #dataviz
nrennie.bsky.social Nicola Rennie @nrennie.bsky.social · Sep 17
The making of this week's #TidyTuesday plot recorded with {camcorder} in #RStats 📊📹
September 19, 2025 at 4:46 PM
jemarnold.bsky.social
Saw a question "what %FTP should my first threshold be at?"

How do we begin to guess? Start with a prediction interval, not a falsely precise point estimate

Data from Sitko et al 2022 helps as a starting estimate (link below 👇)

Any similar datasets? (particularly for female cyclists?)
A boxplot with individual data for FTP (functional threshold power) and LT1 (power at 2.0 mmol/L) in relative power output (W/kg) from 46 competitive male cyclists. LT1 range equals approximately 61-90% FTP, evaluating by rank order across both measures, since paired individual scores are not known. Data digitised from Sitko et al, 2022. Functional Threshold Power as an Alternative to Lactate Thresholds in Road Cycling. https://doi.org/10.1519/jsc.0000000000004070
September 10, 2025 at 3:12 AM
jemarnold.bsky.social
This is really, really good 👀
Model Training and Specification The mean function demonstrated the nonlinear compound curve commonly observed in the MMP data (Figure 1). FPC1 accounted for 79% of the variance and was interpreted as a gain function signifying overall performance (Figure 2, FPC1) as it had the effect of shifting the entire curve up or down. FPC2 accounted for 15% of the variance and was interpreted as a sprint versus endurance bias (Figure 2, FPC2) as it had opposite effects on the curve at short versus long durations. FPC3 accounted for 3% of the variance and was interpreted as a “middle distance” bias (Figure 2, FPC3) as it had opposite effects on the middle durations versus both a short and long durations. It produced right–left shifts in the steep portion of the curve similar to W′. FPC4 accounted for 1% of the variance and lacked a clear interpretation (Figure 2, FPC4). The first 3 FPCs were retained in the F3 model as they were interpretable and represented 97% of the data variance.
August 24, 2025 at 3:08 PM
Reposted by Jem Arnold
captain7bag.bsky.social
New paper with @drphilipskiba.bsky.social is now out: journals.humankinetics.com/view/journal...

We took a new approach to modeling the power duration curve in cyclists using functional principal component analysis.
journals.humankinetics.com
August 19, 2025 at 4:41 PM
jemarnold.bsky.social
Faith Kipyegon & Dr. Brett Kirby using MoxyMonitor #muscleoxygenation #NIRS during training for her 4-min mile attempt coming up now!

They have published how they might be using this information (see links below 👇)

From their promotional bit a few minutes ago
June 26, 2025 at 6:01 PM
Reposted by Jem Arnold
jemarnold.bsky.social
I had the opportunity to contribute to Matt de Neef's wonderful article on iliac artery endofibrosis/FLIA in cyclists

Mostly by knowing where to find the great published diagnostic images, and adding some knowledge we've gained from my recent PhD work on screening and conservative management👇
June 20, 2025 at 12:31 AM
jemarnold.bsky.social
I had the opportunity to contribute to Matt de Neef's wonderful article on iliac artery endofibrosis/FLIA in cyclists

Mostly by knowing where to find the great published diagnostic images, and adding some knowledge we've gained from my recent PhD work on screening and conservative management👇
June 20, 2025 at 12:31 AM
Reposted by Jem Arnold
escapecollective.bsky.social
As many as 1 in 5 pro cyclists will experience a pelvic artery issue during their career. Learn all about iliac artery endofibrosis in our deep-dive feature. escapecollective.com/why-are-so-m...
Why are so many pro cyclists getting iliac artery surgery?
We're hearing more about external iliac artery endofibrosis than ever before, but is it actually on the rise? Plus: what even is it? And how is it treated?
escapecollective.com
June 20, 2025 at 12:17 AM
Reposted by Jem Arnold
captain7bag.bsky.social
This is a really elegant design/result.
jemarnold.bsky.social Jem Arnold @jemarnold.bsky.social · Jun 6
To find COT, knee extension max reps were compared in 'free flow' and with external cuff occlusion

At loads below COT, reps increased exponentially in free-flow conditions, compared to cuff-occluded

At loads above COT, there were no differences between occluded & free-flow 3/
Figure showing number of repetitions for knee extensions at various loads percent of one rep max (1RM) for untrained (UT), endurance trained (ET), and resistance trained (RT) participants. Where reps and total work performed increases exponentially at lower loads in free-flow condition, up to a ceiling at 300 reps (20 minutes of continuous knee extension exercise). While reps and total work linearly increase only up to around 50 reps under cuff-occluded condition, where an external occlusion cuff is inflated during exercise, stopping the inflow of blood.
June 14, 2025 at 8:02 PM
jemarnold.bsky.social
Thoughts about running? Will propulsion phase be above the critical occlusion tension in locomotor muscles? During sprints? Middle-distance? Marathon??

I'd expect it probably is in gastroc at least, based on how mNIRS deoxygenates during incremental running in many athletes 🤔
Figure showing muscle near-infrared spectroscopy on the gastrocnemius (calf) and quadricep muscle during an incremental treadmill running protocol, where gradient was increased at a constant pace. Gastroc muscle deoxygenates at the walk-run transition to a plateau, which is maintained for the remaining approx. 10 minutes of the incremental test. While quad deoxygenates linearly in proportion to the increasing exercise intensity. Suggesting different patterns of perfusion-extraction mismatch in the two different locomotor muscles.
June 7, 2025 at 1:43 PM
Reposted by Jem Arnold
captain7bag.bsky.social
Is COT prior work dependent, W’bal dependent etc ? It can be manipulated by BFR, so I would think W’bal sensitive
jemarnold.bsky.social Jem Arnold @jemarnold.bsky.social · Jun 6
COT represents a phase transition across a range of loads, as occlusive tension increases heterogenously within and between muscles

As likely are all metabolic “thresholds” 👇

COT is muscle & task-specific. How might this apply in sport? 6/
bsky.app/profile/capt...
captain7bag.bsky.social Cap @captain7bag.bsky.social · Dec 15
To elaborate, here’s a visualization from @jemarnold.bsky.social illustrating the number of “thresholds” and how they stack one on top of another. This is what I mean by measuring the width of a mountain peak, at what level do you measure the “width” at what threshold does the peak start ?
June 7, 2025 at 4:28 AM
jemarnold.bsky.social
When does #ResistanceExercise become #EnduranceExercise? 🏋️↔️🏃

It might depend on the critical occluding tension in our muscles 💪🩸

🧵/11👇

A Critical Occluding Tension Phase Transition Occurs Between 30-40% 1RM in Dynamic Knee Extension Exercise
onlinelibrary.wiley.com/doi/10.1111/...
ABSTRACT Oxygen delivery and utilization to working muscle(s) are essential for sustained exercise performance. Higher contractile loads can occlude intramuscular blood vessels, limiting oxygen perfusion, while lighter loads minimize occlusion and allow perfusion. This study explored how external load impacted relative muscle endurance, work capacity, and muscle oxygenation in free-flow and cuff-occluded states to estimate the load at which a muscle occludes itself. Twenty-nine participants (10 untrained (UT), 9 endurance-trained (ET), 10 resistance-trained (RT); 14 females, 15 males) completed repetitions to task failure at 15%, 20%, 25%, 30%, 40%, and 80% of their unilateral knee-extension 1RM in free-flow and cuff-occluded states, with muscle oxygenation (SmO 2 ) measured using near-infrared spectroscopy (NIRS). Compared to cuff-occlusion, greater work capacity and SmO 2 were observed in the free-flow state at 15%–30% 1RM (p < 0.05), but no differences were seen at 40% and 80% 1RM (p ≥ 0.05). In the free-flow state above 40% 1RM, RT participants performed more work than UT and ET (p < 0.05), with no differences between UT and ET (p ≥ 0.05). At 25% and 30% 1RM, ET and RT participants performed more work than UT (p < 0.05), with no differences between ET and RT (p ≥ 0.05). At 15% and 20% 1RM, ET participants performed more work than UT and RT (p < 0.05). These results suggest a load range of > 30% but ≤ 40% 1RM may represent a phase transition in critical occluding tension of the quadriceps, with contractile induced occlusion occurring above this range, and perfusion occurring below.
June 6, 2025 at 2:06 PM
jemarnold.bsky.social
Ever wonder what intramuscular contraction pressure and mNIRS look like during knee extensions to max task tolerance? 🦵🔦

mNIRS SmO2 on left. IMP on right. Look closely! 👀
@matthewfliss.bsky.social PhD project
#SportScience #NIRS #ExercisePhysiology
Desktop on the left shows muscle oxygen saturation (SmO2) in the vastus lateralis from Train.Red mNIRS, showing deoxygenation during repeated knee extensions to maximal task tolerance. Desktop on right shows intramuscular pressure from the same muscle, showing peaks during each contraction, where the magnitude of the peaks tends to increase during the set until near the end where fatigue limits the contraction pressure. Experimental set-up with intramuscular pressure catheter inserted into right vastus lateralis under the mNIRS sensor.
April 24, 2025 at 3:37 AM