Stryd® – Running with power!

There is great potential for power as a running metric but a number of issues to consider before applying it in everyday training.


Price: $199 (circa £159.90)

Purpose: Power monitor for running

Website: [Stry Gen II ‘FOOT POD’]

Summary –      Pros:    Accurate, repeatable, syncs with training peaks /    Cons:  Lack of ability to select specific metrics in IQ stryd watch app / No effective integration of run-power into WKO4

The use of power as a metric for measuring the impact of training and as a tool for optimising performance has revolutionised cycling. However, beyond real time GPS little has changed beyond measuring heart rate from the late 70s and early 80s. This may just have changed with the introduction of power measurement for runners. One version of power meters for running making the headlines has been ‘Stryd®’. I have being playing about with the Stryd over the past few weeks and thought I would share a few findings thus far.

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Figure 1. Photos of the Stryd. Super small & light-weight!


Benefits of power for running

Many of you will already be using power for cycling but the application to running has some significant differences –  for example in cycling the more power you put through the pedals the faster you go. However, in running you could theoretically have increases in power but no increase in speed, but why? The simple reason is you’re locked into a certain position on a bike and the measurement of power simply represents what goes into the power meter via the pedals. This is very different during running as we use power ideally fwd motion, but as you know when we run we move up and down and side to side. All of this non forward movement could result in a loss of forward propulsion from our power production. The take-home not all power results in fwd movement.

Therefore, the Stryd could be a great tool in  assessing the point at which power peaks in faster running and at what point any additional power does not further increase speed.


This type of data can provide guidance in technique development by helping modify our form so that any wasted power (excessive up and down and side to side) can be corrected to result in better fwds movement.

So from a personal point of view I have used cadence on Garmin’s to be more economical in my running. However,  I did not know how to ‘effectively’ apply form changes to impact other metrics such as ground contact time (GCT), vertical oscillation (VO), stride length (SL), vertical ratio (VR) that then show up as faster running or faster running for less effort (thats the goal right!).

Sometime to much information can be damaging if you cannot find a practical home for it. I am all about practical application rather than just measuring something because we can. To that end lets have a look at the Stryd and how we can use it at a practical level.


How Stryd Works?

In essence the Stryd works using 3-dimensional accelerometer and some clever algorithms to estimate power production. According to the Stryd team the product and its data has then been then validated against force plate embedded treadmill in a lab (gold standard of directly measuring force/power).

As such Stryd can measure force production in 3 dimensions (up and down, sided to side and forwards and backwards). This is at a theoretical level is superb as with the right software to extract the data you could not only look at the metrics we see currently on the likes of Garmin 920xt but also some other metrics such as ‘breaking’ during running (something you get if you’re a heal toe runner). Therefore, the Stryd could be an affordable micro-biomechanics lab that could be used not only to measure power (next section) but also to monitor and manipulate in real time, running economy and form (#Free Speed).


Power measurement and running

I have to say this blog has been a bit delayed because I have had in my possession the Stryd for a few months. However, I wanted to have a play about with the stryd in multiple conditions and paces (Intervals vs long runs etc etc) to see what it can and cannot do. Being from a wet and windy part of the UK this has made for a challenge when it comes to finding a dry and non-windy day.

There are a few metrics that are a must have for me when running – pace, heart rate, distance and time. As a new bonus power is now a possible ‘new’ metric to add to that list.


The Stryd App

At present there are 2 apps available for Stryd when using watches such as Garmins 920xt or similar. These can be accessed by the IQ connect and include:

  • Stryd IQ (official app)
  • Stryd 10s power (non-official / unsupported app)

Then we have additional ways to see the data when using and for post analysis:

  • The stryd app for your phone (during running on a treadmill)
  • The stryd online power centre (post run data analysis)

I have had a play with all of these and the phone is nice if you want to see a big screen whilst in the gym, but on the road is not practical. So I will focus on those ‘other’ apps and the data given from the watch displays and via Stryd’s own website ‘the power centre’.

Before that I want to just give a quick overview of some metrics you can get from the Stryd outside of those typically available with a Garmin such as cadence, hr, vertical oscillation, ground contact time etc.

  • Power: The stryd records real-time (instantaneous power) however, there is a workaround app to give 10s average as discussed below.
  • Leg Spring Stiffness: Based on variance in ground contact times (typically less ground contact means running faster and to a point more economically). In general we see swimmers having very flexible ankle (not stiff) and as such transitioning from swimmer to runner is harder.
  • Form Power: This is the power to raise one’s centre of mass against gravity with each step and is independent of speed and gradient. The application of this is when your form (body position etc) is altered to decrease this number is associated with improved economy and reduced vertical oscillation.


My testing of the Stryd

To look at the way the Sytrd works I wanted to check out a few different types of sessions that are typical for most runner and triathlete training sessions. These are the long run (outside) and intervals (treadmill). These are a nice mix of sessions on different surfaces and should be able to highlight the pros and cons from using the Stryd and its related software.

Before we start using the Styd we need to find out our training zones. For me these are carried out during a lactate threshold test (see previous blog on BSx). From that test set training zones are based on Hr, Pace and Power.


The Power Centre: Analysis (Pro’s and Cons)

The 1st session was intervals (warm up, then 3 x 11Min reps at 3.45/3.45 min/km or 6.15min/mile if you like imperial). As you can see below (Figure 2) we get some nice square wave power level shapes (orange line) for each fo the 3 intervals. When doing bike intervals and using a power meter these shapes are very similar, and like using power on a bike we can see a lag in the heart rate (purple line) getting up to 160bpm (the goal pace for mid to upper Level 3 work).

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Figure 2: Stryd’s online power centre – Data analysis from Interval training on a treadmill.


The lag in Heart Rate for me was about 5-6 mins before hitting what would be level-3, therefore power allows us to instantly work in the right zone rather than consistently upping or lowering pace until you hit the right the heart rate. However, it could be said why not just set our training zones off pace as that’s a way to cut out the delay (lag) in heart rate rising to the hight level?

Well again we have external issues than can increase or decrease the physiological demand (effort) of maintaining a specific pace. Pace does not take into consideration the effort it might take to get up or down a hill or running into a head wind. What’s great is that (theoretically) using power would make issues as weather (wind) and terrain (hills) irrelevant to a large degree – resulting in consistently hitting the right training zone in every session.

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Figure 2: Stryd’s online power centre – Data analysis from easy long run!


The figure above shows some metrics from a very easy zone 2 run and from it you can see the blue line showing pace (min/km) and its nice and steady and tracks closely with orange line (power) below.

At present what I don’t like from using the Stryd is the variability. The power measurement (see the orange line above) is taken in real time. As such its readings of power jumps quite often (unlike the trace we get on a treadmill – see orange line on Figure x) as power can fluctuate from second to second. The result is constantly checking your watch to try and stay in the right power zone. This is not great and a distraction when it comes to pacing a workout on the road.

The solution to this would be to have the ability to see and average of power measurements over say 5-10 seconds as we can do with power as measured using a Garmin on our bikes or like average pace on a watch. The averaging effect would smooth the values (variability) you see on your watch, making running at a constant power more achievable and less stressful. I will discuss the possibility of a workaround for this in the ‘Watch App’ section below.


Figure 3: Stryd’s power centre – Lots of metrics available on the power centre for data freaks.


When you use the power centre there are a whole host of data fields that can be looked at (See Figure 3 above). But for my own view there are only a few that seem of interest at this time. ‘Form power’ (see the ‘Stryd app’ section above for what this metric means) and ‘cadence’ are the main 2 beyond power.

When you run (On a treadmill) is easier to keep a check on ‘form power’ during the session. My view is that keeping form power low is typically due to leg turnover (cadence) and also how you toe-off when running. It provides some pretty quick feedback and typically as form power drops you will also see the power to maintain a set speed falls (more efficient?).

What I cannot say is how this metric is useful across a range of abilities. For myself whilst I don’t have a very high VO2max, my running economy is very good as is my cadence. Therefore, I do not see a huge benefit for an economic runner. However, in others I see run cadence a major issue in them becoming more economic. Many can achieve high (>180) cadence figures when running at 5-10k pace but this drops of significantly as the distance increases and pace drops. I believe that truly economic runners with good form will hold a cadence of circa 180 almost irrespective of run pace (recovery vs. marathon).

As such I see some nice options from the metrics but outside of ‘form powder’ and ‘cadence’ I think they are just nice metrics to perhaps compare overtime (something you can do in the power centre i.e. compare metrics from one workout against the same workout a few weeks later).


 The watch app

The biggest downfall of the Stryd is the watch app. The primary App is available from the GARMIN connect store (Stryd IQ). The app allows you to download the data post run to the power centre and also to training peaks. the issue is that there is no ability to decide what metrics you can see on each data field. You simply have to accept the data fields the app allows you to see with power.

watch app

Figure 4: Watch metrics – well at least the useful ones!


You also cannot alter the sampling rate for power i.e. per 3, 10, 30 Seconds etc. As above this causes some issues. There is a workaround for those wanting average power and that’s in the form of an app from the Garmin Connect IQ store called ‘Avg Power 10s’. This is the metric I now use on my runs but unfortunately it does not record the power data from that session – so although you can see the data field during the run (average 10s power) and your other chosen metrics such as heart rate and pace etc its not downloadable. It’s also not supported by Stryd.;jsessionid=A8BF8154DDBF09E083FF08EEB10F970A


Is it fit for purpose: Future proofing?

There is great potential for using power for run training and racing but there are still some significant issues to be resolved. I live in the north of the UK and we can get some real windy days and the effort to run in side winds are not fully transferred into the Stryds power measurements in my experience. As such to measure physiological effort in such conditions you need to fall back to heart rate.

However, in days where wind is below 10mph the Styrd is spot on in its accuracy and reproducibility. You can set you training zones using the stryd but take care on what surface. You will get different readings depending on the surface you run on. In my own testing the harder the surface the higher the power recorded. From one treadmill to another despite the same gradient and speed there is circa a 10w difference. Therefore, you will need to build in this when considering your training zones and perhaps power to use if for a race on the road vs. off-road / x-county.

The app needs a major makeover – its very ridged and at this time its not very intuitive in setting it up. What you want is the ability to connect to Stryd as you would a heart rate monitor and for your Garmin to know that and then you have in the field data options all the potential metrics available. Metrics such as those in the power centre plus and ability to look at average power for laps, 5, 10, 30 seconds etc. This will no doubt require more co-operation between Stryd and Garmin and other watch makers.


Downloading Data

The final issues relate to training peaks. The only data that gets downloaded is power but no ‘form power’ or ‘LSS’ or similar metrics seen in the Stryd power centre. The other major issue for me personally is the data that shows up as power on training peaks does not sync with WKO4. As such when you want to do some in-depth analysis your cannot use power i.e. the whole point of using the Stryd.

There is also I am sure some other great metrics that you could get from the Stryd but just not accessible ‘yet’. Because it measures 3d power with the right software we could get values related to heal striking (breaking). This would be a valuable metric for helping alter run form and from what I hear from Stryd its something possible for the future.

I know from following the Stryd forums and asking staff about the issues of setting up the app etc that they are trying to resolve these early adopter issues. Similarly, the WKO4 team are working on an update for Stryd but as of yet not timelines have been released.

Altium i-10

Altium-i10 – Like being on top of a mountain?

Price: £499 (Circa $617)

Purpose: To deliver the benefits of altitude training at home.


Summary – Pros: May work in swimming / Cons: Expensive, no clear benefit on lactate threshold or power at lactate threshold, no effect on hct and hb.

For elite athletes high altitude training has been regarded as ‘must have’ component in the preparation for elite endurance sports. The reason for this is that hypoxic (low oxygen) stress at altitude (note this ‘at altitude’) facilitates key physiological and biochemical adaptations that may improve performance at sea-level. In order to tap into the beneficial effects of altitude adaptation and performance enhancement comes the Altium i10 a piece of equipment that allows you to breath a lower level of oxygen (resulting in hypoxia – low blood oxygen) followed by normal breathing (reoxygenation). The intermitted hypoxia (IH) is suggested to trigger a response similar to that obtained at altitude. It’s as simple as that.


Figure 1. Photos of the Altium i10

A closer look…

When you receive the Altium it comes in James Bond style case and this is a nice touch for something that is ultra-premium in its costs of circa £500. Inside we have a cylinder that you can place some circular sponges, and some poppers that can work to alter the flow rate and chamber volume which both impact breathing. For a great explanation and some additional detail check out


Figure 2. From Top left to right – Altium taken apart, pulse oximeter, foam disks to alter chamber volume, CO2 scrubber cartridge and mouthpiece, flow controller.

The Altium oximeter links to an app for your iPhone which shows your O2 levels and pulse and most importantly tells you when to start and stop breathing on the Altium (6 minute on with 4 mins rest for each interval). At the end of the 1 Hour session you get a summary for each of your 6 intervals showing how long you spent at certain levels of O2 and what that equates to in relation to altitude. The app then gives you a summary of all session and converts them into what they term ‘ALTIPOINTS’ – the more time at higher altitude the more points.

I have to say the 1ST few sessions took some playing about with to get the volume of the cylinder and the flow rate just right so that your O2 levels didn’t drop to low. If they drop to low the app stops recording until you O2 gets back up to what they view a safe range. I found this really irritating aspect of using the app and the Altium but I can see why the do it i.e. safety and to stop you passing out. However, I would love and option to just switch this off.


Figure 3. Altium accumulated scores and example of o2 results from a 6 minutes sessions as recorded on the Altium i10 App.

The other issue is you need also to get use to when the CO2 scrubber has to be changed. This becomes obvious if you know what to look for and this indicated by either, 1. Colour change in the CO2 scrubber from white to purple, 2. The O2 levels become difficult to keep low no matter how you breathe. OK so that’s how it works but what about the science behind it?

Some science

Over the past decade, the use of hypoxic training techniques has become increasingly popular, especially living high (altitude) and training low (LHTL). Traditionally, this LHTL protocol requires long exposure time of >12-14d to receive a sufficient ‘hypoxic’ impact that adaptation and performance benefits result. As such the duration such an intervention can be prohibitive for many athletes due to cost and availability.

Another model is live low and train high (LLTH) where exposure to hypoxic conditions are of shorter duration (<3hr, 2-5 x a week). However, this duration has been shown not to deliver the benefits of LHTL and LLTH methods.

With reference to the Altium another short duration (<3 h) hypoxic technique is intermittent hypoxic exposure (IHE) where no training is performed during exposure sessions. This has been show through a comprehensive review of published studies up until 2010 concluded that IHE alone does not lead to sustained physiological adaptations or improved exercise performance.

However, another study looking at published research concluded that IHE may improve performance in sub-elite athletes, but not elite athletes owing to the fact that elites experience more hypoxia from their day-2-day higher intensities of training compared with sub-elite athletes. Some additional study data from 2014 shows a single 4-hour exposure at 300m with no impact on genes related altitude adaptation.

One study looked at IHE (7 x 1 hour/day at 4500m at rest) and its impact on physiological responses (at 2 submaximal workloads at simulated altitudes of 2000 m, 3000 m, and 4000 m). Subjects where tested pre and post altitude exposure and the results showed blood lactate concentrations and CO2 output were reduced following altitude exposure. It was suggested that the effect might have been caused by an improvement in aerobic power resulting in lower relative exercise intensity after IHE. However, based on the study data it is not likely that aerobic power was improved because neither haematological parameters (i.e. haemoglobin concentration) nor heart rate as an indicator of relative exercise intensity had changed after the IHE application.

Furthermore, the study did not assess exercise performance so although there may have been some physiological changes there was no proof of a performance benefit.

The Altium Study: University of the West of Scotland Study (UWS)

The Altium from what I can find has been tested at a University but at present the study is unpublished. The study on 13 competitive cyclists and triathletes used the Altium every other day for 28 days (14 sessions) using 6 mins of Altium breathing and 4 minutes off for 60 minutes per session. Prior to and post Altium use subjects underwent a lactate threshold test followed by a V02max test.

The results of the study state the use of the Altium:

  • Improved vo2max [+2mls/kg](UWS study)
  • Improved lactate threshold [+18watts) (UWS study)
  • Improved cycling efficiency (UWS study)
  • Improved time trial performance (UWS study)

There where no changes to haemoglobin (oxygen carrying protein) and haematocrit (amount of oxygen carrying red cells).

Therefore, the results of the IHE study (7 x 1 hour/day at 4500m at rest) I discuss above may suggest the results on the Altium from the UWS may be effective if these responses translate to a performance effect. To date other than Altium’s own unpublished (not in peer review journal not conference abstract) research carried out at the UWS there is no direct evidence to show that the suggested method of use of the Altium i.e. 1 hour per day for 14 days or every other day for 28 days deliver performance benefits. I asked the makers of the Altium for a rationale based on published data that supports the protocol but none was provided so I cannot say what the basis is for the way the Altium is suggested to be used.

One other issue and this is important – Altitude is not only about low levels of oxygen in the body. There is also the issue of ‘Partial pressure’ of oxygen.  As we get higher (increase in altitude) the pressure decreases and although the percentage of oxygen we breathe in remains the same (circa 21%) the number of all molecules in the air including oxygen decreases. Therefore, the low oxygen tension (pressure) in the air we breath results in low oxygen availability. Therefore, unlike the Altium the way oxygen availability occurs at Altitude may result in different effects on the body.


I have to say from the outset I am only ‘one’ subject (a case study) and in science this would be viewed as a case study therefore my results may not be representative of others using this product. However, that does not make my results (see below) irrelevant in relation to my own experience and benefits from using the product in the absence of a peer reviewed study.

As with any piece of technology ‘free speed’ or ‘free performance’ benefits without having to train to get them are a great idea. As with this and other blogs I want to try them out to see if they really work, especially if they come with a big price tag.

OK let’s get down to the results….

What I did…

The pre test for the Altium was pre (19th August) and post (September 9th) with use of the Altium for 14 days starting on the 24th August and last day of use 7th September (14 days).

So for the actual testing we carried out a Lactate threshold test following the same protocol as per the BSX (See my previous BSX blog). That means each stage lasting 3 minutes and increasing 20 watts per stage.

During the test blood lactate was taken for every stage as was inspired and expired O2 and CO2. Also pre and post-test haemoglobin and haematocrit was measured.

During the test I also wore the BSX insights as a secondary measure to assess lactate threshold (and blood measures of threshold pre and post match almost identically to that of the BSX).

The results…

The following is the data from the test results but first its important to establish the rate of change in fitness and adaptation occurring through my training alone. As such the first figure shows a number of lactate threshold tests taken around every week with the BSX building up to the laboratory tests. As you can see there is a steady increase in watts at lactate threshold of about 3/4 watts per week.


Figure 4. BSX threshold results up 1 month pre-testing of the Altium

This data is useful as it can be used to see if the Altium really changes performance above that from exercise alone. Most blogs and reviews I have seen on the Altium have said they think it worked but because I was not consistent in my training or they didn’t measure effects of training on performance and or LT running up to the test we don’t know for sure if it’s the training or Altium causing the performance enhancement.

As such my monitoring pre use of the Altium I believe makes this review very relevant and tightly controlled.  The BSX demonstrated that over the course of using the Altium – threshold increased circa 5/6 watts, which was not different from the June from July 17 to July 26th.

Results pre and post Altium use.

Lactate threshold: The impact of the Altium pre and post-test did not increase watts at threshold (250w based on blood analysis, slightly higher by the BSx) to a greater extent than the improvements occurring as a result of training alone. As such the Altium seems not to result in a beneficial impact on lactate threshold (See figures 5 and 6).


Figure 5. BSX results pre (19th August) and post (September 9th)


Figure 6. Lactate threshold pre and post Altium use.

Haemaglobin, hematocrit and VO2max:

Hematocrit is a measure of the proportion of blood volume that is occupied by red blood cells. The higher your hematocrit, the more oxygen can be delivered per volume of blood.

Haemoglobin is a protein that binds to oxygen in the lungs so that the oxygen can be transported to the rest of the body. Therefore, increasing the amount of haemoglobin in the blood increases the amount of oxygen that can be carried and is a feature of altitude acclimatization.

A normal value for hemoglobin is 13.5 to 17.5 grams per deciliter (g/dl), and 38.8 to 50% for hematocrit. As can be seen from Figure 7 my values are in the normal range and although these values can be impacted by hydration and training status they did not significantly change over the course of using the Altium. This result was expected and not something that the company behind the Altium have suggested would alter and confirms the results in their UWS study.

Because Hb and Hct they can be reflective of a change in oxygen carrying capacity they are worth testing pre and post-test. As we know the are limits placed on athletes by the likes of the Union Cycliste Internationale (UCI) for a haematocrit of 50% and international skiing federation (FIS) 18.5 g/dl for hemoglobin. This is in a bid to stop and detect the use of EPO therefore any big effects from the Altium would have been important for athletes undergoing such testing.


Figure 7. Pre and post haemoglobin and haematocrit values.

VO2max is the volume of oxygen can be consumed while exercising at your maximum capacity or often called your maximal aerobic capacity. Unlike hematocrit and hemaglobin the effects of altitude on VO2max are not clear with some studies showing an increase but others have shown a decrease as the body becomes more efficient at delivering oxygen for the same intensity of work.

We also tested VO2max levels pre and post the use of the Altium and in Figure 8 we can see that pre and post use there where no significant changes in VO2max.screen-shot-2016-12-21-at-14-43-12

Figure 8. VO2max (absolute) measured pre and post Altium use.


The 1ST thing to say is I only measured the impact of the Altium i10 on ‘cycling’ performance and physiological changes during a cycling test. Therefore, it is possible there could be performance benefits for running and or swimming.

There are also limitations in the test in so far as the measurement of VO2max as would normally only be measured during shorter duration test time frame i.e. 10-15minutes. However, the conditions of the test pre and post Altium use are the same and therefore the maximum VO2 reached is relevant.

Furthermore, threshold (lactate) maybe determined using different mathematical models and this can significantly impact the results of the test out come. As such we used a selection of methods including logging the data and visually examining threshold, used a modified dmax method, also used the BSX insights. All demonstrated no significant improvement in threshold pre and post Altium use. We have not inserted the lines on figure 6 above as we feel even the non-scientist can see the blood values do not differ significantly pre and post Altium use.

Future and benefits

Before I give a final conclusion I can say I wished I had completed a critical speed or some other performance test for swimming. The reason is I felt that there was some significant gains over the course of using the Altium.

Now this may be as a result of training or training plus the Altium I don’t know as I didn’t take a measure of swim performance running up to Altium use or post use. Anecdotally I can say that swimming became faster over the weeks and the perceived exertion was lower. My feeling is that this might be the right home for the Altium as swimming aid and by its very nature swimming is hypoxic especially for those breathing less every stroke. As such the exposure to higher CO2 / lower O2 my impact the bodies tolerance and as such the need to breath. The result would be perhaps an ability to maintain a more efficient head down position in the water thereby making the swim more streamlined and faster. Clearly more work needed here.

In relation to cycling my ‘own’ results simply don’t warrant the Altium as a performance enhancer (no increased watts at lactate threshold, changes in haemoglobin or haematocrit or VO2max). As such for me the expenditure was not worth it as it did not benefit performance beyond what I was experiencing with training.

For the makers of the Altium I feel there is a lot more work to be done on the testing side and specifically the development of the protocol. So would a 7 day 2 hours a day protocol have impacted my results differently (i.e. greater hypoxic stimulus but more acute) to the current protocols?

What about the maintenance phase? Where is the evidence for this?

What about a study assessing the effects of the Altium in more hypoxic sports such as swimming? Those who have completed an Ironman swim know exactly how hypoxic that can get and perhaps there is something to be said for the Altium in that regards.

There are issues of blinding. Blinding relates to the fact knowing you using a product you believe enhances performance results in enhanced performance through placebo effect. By using a mix of a product or protocol that does not lower O2 vs the Altium and its suggested protocol we can assess if any performance benefits are delivered by placebo (i.e. subjects are blinded to using a performance enhancer). However, that said when using this sort of equipment its unlikely watts at lactate threshold can be impacted.

Similarly, care should be taken over the run into any program over the training status and rate of performance improvements athletes are undergoing. So for my test we measure threshold in the 4 weeks pre testing to see the improvements to be made on a week-by-week basis. Similarly, the volume and intensity over the 2 weeks of the Altium use was similar. Was this assessed for the testing done by UWS?

Finally, price point – this is a big punt to spend almost £500 and for that I think most consumers want a guarantee of efficacy. But these are the risks of early adoption of technology.



Wilber RL, Stray-Gundersen J, Levine BD. Effect of hypoxic ‘‘dose’’ on physiological responses and sea-level performance. Med Sci Sports Exerc. 2007;39(9):1590–9.

Billaut F. A higher calling, but does altitude training work? 2011. Accessed 10 Oct 2012.

Millet GP, Roels B, Schmitt L, et al. Combining hypoxic methods for peak performance. Sports Med. 2010;40(1):1–25.

Bonetti DL, Hopkins WG. Sea-level exercise performance following adaptation to hypoxia: a meta-analysis. Sports Med. 2009;39(2):107–27.


BSX Insight

BSX insights – Physiological analysis for a fraction of the cost?

Price: $419.99 (circa £339)

Purpose: Lactate threshold sensor


Summary – Pros: Accurate, repeatable / Cons: Cost, limited to only assessing threshold.

picture1When I find blogs online you find the writer waffling on for ages before getting to the take home. So if you want to find out what we found out when we took the BSX to a lab to test then jump down the page to “TESTING THE BSX IN A LAB.The following provides a background to lactate testing and how the BSX works which helps understand what we tested and what are the potential pros and cons of the BSX.

One of the most important pieces of information all athletes and coaches prior to setting up a training program is the development of accurate training zones (TZs). TZs are levels of effort based on heart rate, power, pace or perceived effort that correspond to certain energy systems in the body.

In order to effetely and more importantly accurately set these zones we need to determine what is considered a ‘threshold’ between aerobic and anaerobic energy systems.

Traditionally, this threshold has been calculated from maximal heart rate or heart rate formulas or from laboratory testing involving analysis of blood lactate or the relationship between o2 and Co2 levels. These different measures vary in accuracy and vastly in cost  – from nothing more than placing your age, resting and max heart rate into an equation, to carrying out a 20 minute all out effort and looking at pace or watts for a given heart rate. Or use of the gold standard the most expensive lab tests conducted by an exercise physiologist with specialist equipment such as lactate analysers and colorimeters (See end of blog for some online help about these methods).

The drawback about lab testing is primarily ‘cost’. It maybe £150-400 for a lab based threshold assessment from which training zones are developed. Although a one of payment of this amount maybe acceptable, as we train we adapt, therefore our thresholds will alter requiring re-testing every 10-12 weeks. The cumulative costs over the year(s) are not insignificant.

However in March 2014 the launch of a new product was an attempt to give the power to assess lactate threshold back to the consumer in a convenient, accurate and cost effective package.


How the BSX works

This could be a whole book worth of discussion but for the purposes of this blog the basics will be enough as really the most important issue is will the BSX measure as accurately as current gold stand tests used in a lab.

Haemoglobin is one of the most important molecules because of its oxygen-carrying ability. The basic principle of the BSX is the measurement of blood haemoglobin concentration in addition to blood O2 saturation. It does this by shining near-infrared light onto the skin and detecting some of the

light after it has travelled into the muscle tissue and returned to the surface. Because oxygenated and deoxygenated hemoglobin (chromophores) have different absorbance spectra (color recognizing) in this region. Because the hemoglobin has to pass through different tissues and as such the way light passes through these tissues (i.e. some people fatter than others) can impact the measurement of levels of oxygenated and deoxygenated heamoglobin. Therefore, equations are used to overcome these issues.


The take home is that the ratio of the oxyhemoglobin (oxygenated hemoglobin) to the total hemoglobin concentration is reported by BSX as a percentage (SmO2). SmO2 stands for muscle oxygen saturation and is the percentage of hemoglobin that is carrying oxygen in capillaries of muscle.

As exercise intensity increases and we need greater levels of Oxygen and as such SmO2 (oxygen saturation) decreases. The measures of SmO2 as an index of oxygen extraction is measured noninvasively by the BSX and may offer a method of identifying a threshold related to anaerobic capacity.

The relationship between SmO2 is and exercise intensity is linear, but also at higher levels demonstrates a breakpoint (deflection) in the relationship, which has been shown to correlate to lactate threshold. In plain English at a certain point the change in SmO2 is not constant as we see in lactate threshold tests.

Possible issues with the hardware & software


BSX is a near-infrared spectrometer (NIRs) and with such equipment when used in human physiology there can be problems with accuracy and the data that is transmitted. One significant issue can involve the reflection of light that comes from the muscle. If light where to get from a source other than the muscle this could impact and data used to estimate the threshold results of the BSX. Therefore, the use of the sleeve that the BSX system uses to hold the sensor should be either 1. Tight enough to hold the sensor against the skin so light does not escape when reaching the sensors, 2. The sleeve should ideally block and light from hitting the sensors.







Therefore, if we just accept that the sleeve is great quality and ideally light blocking it would be key to make sure the sleeve is in optimum condition (no holes etc) and also that it is the right size so to place enough pressure onto the sensor that rests on the calf. The sleeve also must not be too tight as this may restrict blood flow and as such impact the results.

These issues suggest that using the BSX during cycling where there is less bouncing and movement of the sensor results may deliver more accurate threshold data than during running. In addition, differences in bodyfat levels as discussed above may also impact the accuracy of BSX. However, I would view this as a minor issue as the equations used to translate the light signal to usable data (i.e. a threshold number from a breakpoint) would I believe considered this. The equations that BSX uses to calculate are not declared and as such we have no way of assessing that issue.


The software (a downloadable app) decides the intensity / stages of the test by using a series of questions including:

  1. What is an easy, conversational power (watts)?
  2. What is your current 40k race power (watts)?
  3. Consecutive months of training?
  4. How many days do you train per week?
  5. How many kilometres do you train per week?

From this the software comes up with a graded exercise test where you begin at a set power over a number of levels, which are 3 minutes in duration. We believe in general this is circa 80-120w starting intensity that increases 20w every 3 minutes until exhaustion.

How these questions predict the level in the test are unknown but the test can be very long compared to a traditional lab based lactate threshold test that also incorporates a maximum oxygen uptake vo2max test (example in my test it took circa 30 minutes). However, as a standalone lactate test it would not be too difficult for a trained subject to carry out, but for an untrained person a 30 minute test may cause some concern.

Finally, we don’t know what method the test uses to identify where the threshold occurs. This has been a topic of debate for many years in exercise physiology and relates to how we identify where the relationship between lactate increase moves from a linear (steady state) increase during the test to something occurring at a much higher rate (the breakpoint in that relationship).

Many equations have been adopted to try to identify this and all with pros and cons depending on the test (bike vs. run), fitness, protocol of the test (duration, intensity of each state) etc.


I am a sceptic by heart as are all scientists and as such I wanted to make sure the product did what is says on the tin and can really identify lactate threshold. As such I booked some time out at a local University to test out the accuracy of the BSX against actual blood based lactate threshold measurement.

The test protocol was performed according to the BSX manufacturer’s Instructions as given on the phone app. So after an additional 100w warm-up stage the protocol started at 140w and increased by 20 W every 3 min until I could no longer maintain the power output (end stage 10 ‘300w’). 5 weeks later the test was repeated.

The Results…It’s all good!

In the figures below are the results of the tests from the raw data from the BSX (sm02) and the blood tests (lactate vs. watts) carried out in the lab. The test results demonstrated almost exactly the same breakpoint using the BSX and the lab tests (not breakpoint in SMO2 is visual but the BSX gives an actual number of watts (258)).


Figure 1. Lactate threshold data from BSX and blood lactate test.

In the Figure 1 above the BSX shows a clear break point (deflection) representing the equivalent of the lactate threshold as measured using blood lactate. The only difference is that the threshold occurs slightly earlier than that in the BSX test as the BSX measure changes in oxygen levels instantaneously, whereas blood lactate levels take time to change as lactate leaves the muscles, then into the blood where it is taken and measured following a finger prick blood test.


Figure 2. Threshold values as shown in the BSX app and related TZs


These results are great news for those of us that want an accurate reflection of where the threshold occurs rather than a best guess typically associated with tests such as functional threshold capacity (FTP)[I will address FTP in a future blog].

However, despite the results there are some limitations over traditional lab tests that also measure oxygen uptake during a lactate test. The measurement of oxygen uptake and utilisation (known as metabolic testing) can also tell us about our use of fuel i.e. the % and rate of fat and carbohydrate use. This is essential to know how long we could exercise for at a given intensity (i.e. watts/pace) before we would begin to run out of fuel and fatigue. From such data we can calculate how much carbohydrate we would need to take in over the course of an Ironman or Sportive to ensure we don’t fatigue. Furthermore, metabolic testing also allows us to assess metabolic efficiency, which is the amount of oxygen needed to generate a given effort (i.e. o2 per km).


Although I did not get to test the BSX insights in relation to its ability to identify threshold during a run vs. the lab comparison supports its accuracy and is clearly very close to what was obtained in the lab. Of course the lab test was only based on me ‘one test subject’. As such a study with greater numbers may deliver different results.

For now the study demonstrates the BSX is a cost effect means of determining lactate threshold, is easily usable and the results are repeatable.

Training Zone calculation

Heart rate equations:

Colorimetry (Lactate threshold indirect):

Lactate Lactate threshold direct:

Indirect from 20min (FTP) test:

Running pace zone calculator: