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Jem Arnold Profile picture
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Jan 9 • 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) ?
ok the more I think about this, the less 🤯 it seems

Consistent with what we know about intensity-dependence of eg. mito biogen

I think I just found a nice new-to-me perspective on training stimuli & adaptations, which I'm trying to understand better #thinkingoutloud
eg peripheral & central effects of HIIT & SIT, from my colleague's PhD thesis (not the thesis I was reading)

Where can I learn more?

tspace.library.utoronto.ca/handle/1807/10…

researchgate.net/profile/Michae…

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More from @jem_arnold

Jem Arnold Profile picture
Jan 7
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
⬆️SmO2 across bouts in HIGH SF group (blue):

⬆️SF ⇒ more optical signal comes from non-metabolically active skin & adipose with ⬆️ thermoregulatory blood flow as ⬆️body temperature

Hence ⬆️⬆️blood flow relative to 🟰O2 extraction ⇒⬆️SmO2 in superficial tissues
3/5
Read 5 tweets
Jem Arnold Profile picture
Dec 8, 2022
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
Cycling TT performance was improved by both SIT and HIIT

Long (>4min) HIIT was modestly more effective than SIT
3/7
Read 7 tweets
Jem Arnold Profile picture
Nov 4, 2022
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/
@cwiggs5 @DrMJoyner et al 2021 performed submax constant workload exercise and found no differences in oxygenation overall, but observed a subset of subjects (25%) who had greater deoxygenation in aero. They note the importance of individual responses 3/6
doi.org/10.1002/tsm2.2…
Read 6 tweets
Jem Arnold Profile picture
Oct 29, 2022
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/
3/15
Barstow has a comprehensive overview of technically and biologically important aspects of NIRS, with recommendations for standardised methodology and nomenclature. This is a must read IMO for starting to understand the nuances of NIRS interpretation
pubmed.ncbi.nlm.nih.gov/30844336/
Read 17 tweets
Jem Arnold Profile picture
Aug 9, 2022
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
Which leaves us with not much room to expand into the 'middle-RPE mush'

~3-6/10 RPE can be hard to tell apart

Maybe cue:
• start to feel the squeeze in the quads
• controlled belly breaths
• settle into stable hips, core, neck, shoulders Image
Read 5 tweets
Jem Arnold Profile picture
Jun 1, 2022
Lactate curves in a 5-1 multi-stage cycling test across workload (W/kg). Modelled with VO2peak (range 44-74 ml/min/kg). ↑ Wpeak ∝ ↑ VO2peak along x-axis.

Nice to see the expected longer steady-state achieved by higher fitness subjects before inflection point 1/2 Image
I think the really interesting trend is BLa plotted on relative workload (% individual Wpeak, as proxy for intensity).

Higher fitness:
Longer steady-state
Nadir at ~60% Wpeak (vs no nadir)
Inflection starts at higher intensity
Higher BLa at Wpeak (higher La- flux?) 2/2 Image
Ok, might as well look at Fat oxidation while we're here 😁 Plotted on normalised workload (W/kg) 3/4

Looks like FatMax (W/kg) occurs within ~1 stage (0.5 W/kg) of BLamin
Bias = 0.09 W/kg
95%CI Limits of agreement = -0.5-0.7 W/kg
Pearson r = 0.84, 95%CI 0.71-0.92 Image
Read 4 tweets

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