Jem Arnold
LightNews LightNews
banner
jemarnold.bsky.social
Jem Arnold
@jemarnold.bsky.social
590 followers 350 following 300 posts
PhD candidate & physiotherapist | 🩸Iliac artery endofibrosis / FLIA | Endurance testing & NIRS.
Treat declarative statements as questions?
Posts Replies Media Videos
Pinned
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
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
Reposted by Jem Arnold
katewagner.wehwalt.net
wrote about pogačar's roubaix experiment for @escapecollective.bsky.social escapecollective.com/a-tantalizin...
A tantalizing near-win sends Pogačar back to the forge
Undone by an atavistic race that harshly punishes even the smallest mistake, Tadej Pogačar learned that it's not as if he can't win Paris-Roubaix; he simply didn't.
escapecollective.com
April 13, 2025 at 7:46 PM
Reposted by Jem Arnold
jemarnold.bsky.social
Collaboration is hard and rewarding. Antagonism is easy and unproductive.

Thanks to IJSPP for this editorial on collaboration in sport & exercise science

I hope we will continue to share knowledge with such generous and excellent colleagues in science

journals.humankinetics.com/view/journal...
Editorial in International Journal of Sports Physiology and Performance, (Ahead of Print) from author Jos J. de Koning (Department of Human Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands) titled "Cooperation Takes Us Further" DOI: https://doi.org/10.1123/ijspp.2025-0100
April 3, 2025 at 3:17 PM
jemarnold.bsky.social
Collaboration is hard and rewarding. Antagonism is easy and unproductive.

Thanks to IJSPP for this editorial on collaboration in sport & exercise science

I hope we will continue to share knowledge with such generous and excellent colleagues in science

journals.humankinetics.com/view/journal...
Editorial in International Journal of Sports Physiology and Performance, (Ahead of Print) from author Jos J. de Koning (Department of Human Movement Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands) titled "Cooperation Takes Us Further" DOI: https://doi.org/10.1123/ijspp.2025-0100
April 3, 2025 at 3:17 PM
jemarnold.bsky.social
A number of big name riders in the Women's & Men's peloton who have returned from surgery(ies) for iliac artery endofibrosis in recent years, in light of the news on Fabio Jakobsen (article in Dutch)
March 31, 2025 at 10:16 PM
jemarnold.bsky.social
Ah, sorry to hear this but glad he can get treatment

Bilateral flow limitations are thought to be much less common in cyclists (<15%) but we think there may be higher prevalence with the "unaffected" leg still showing some functional limitations
👉https://www.mdpi.com/2077-0383/11/24/7462
March 31, 2025 at 2:43 PM
jemarnold.bsky.social
Smart people discussing how to model power-duration data from first principles 👇
captain7bag.bsky.social Cap @captain7bag.bsky.social · Mar 25
@rchung.bsky.social Have you ever published or presented the use of the convex hull on work duration data? Anything that I could cite?
March 25, 2025 at 2:24 PM
Reposted by Jem Arnold
aartgoossens.bsky.social
I have managed to do this with an asymmetric cost function. This is the OmPD model but it works similar for other models.
The challenge is how "asymmetric" the cost function should be so it allows for "gaps" (i.e. sharp declines) in the mean-max data but still stays close to the data.
March 25, 2025 at 9:48 AM
jemarnold.bsky.social
New longitudinal study in female rowers @drake-eserhaut.bsky.social comparing mNIRS oxygenation breakpoints & resaturation with lactate thresholds

As expected, LTs != mNIRS-BPs for individual athletes.

We need more longitudinal mNIRS research like this! But where are the performance outcomes? 👀
March 22, 2025 at 5:45 PM
jemarnold.bsky.social
Validation of Xert? www.xertonline.com? 👀👀

I've really liked the Xert model better than classic CP & W'. Another one to look forward to for my weekend reading list!
hilkkakontro.bsky.social Hilkka Kontro @hilkkakontro.bsky.social · Mar 20
Accumulating work at different intensities relative to CP, Pmax, and remaining W' results in somewhat distinct adaptive responses, which should be taken into account when trying to model training and predict performance gains.
March 20, 2025 at 10:57 PM
Reposted by Jem Arnold
hilkkakontro.bsky.social
Our new preprint proposes a new way to quantify training loads based on power output. We describe how a 3-parameter CP model may be used to estimate contributions of each energy system, resulting in a "strain score" which overcomes some limitations of other TL metrics. doi.org/10.48550/arX...
March 20, 2025 at 11:47 AM
jemarnold.bsky.social
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% improvement in VO2max was associated with a negligible +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.
March 20, 2025 at 2:43 PM
Reposted by Jem Arnold
supportchampions.bsky.social
This week Dr Steve Ingham is joined by Michael Rosenblat as they discuss how training modal impacts VO2 max and time trial performance. He explores training intensity, distribution and oxygen uptake and how heart rate lag can impact interval training.

• Listen and watch on your usual platforms
March 19, 2025 at 9:00 AM