Angular Velocity Based Training - What It Is And Why We Developed It

Introduction

At Output Sports, we’re an interdisciplinary team of Sports-Scientists, Data-Scientists, Physios, Biomechanists and Engineers. Some of our earliest work, during our PhDs, focused on developing accurate technique assessment of S&C and Physio exercises with a minimal sensor set. As we progressed from the research lab to launching Output Sports, we added more and more performance metrics to our systems based on the requests of our global community of sports-practitioners. Our recently released angular velocity-based training merges our early work on technique assessment in S&C and our more recent work on performance measurement.

Lab Data And Practitioner Ideating: Why We Developed The Strength Pathway (A-VBT)

During our founders’ (Dr. Darragh Whelan & Dr. Martin O’Reilly’s) PhD research we developed a number of machine-learning based classifications systems for analysing compound exercises with wearable IMUs. This included work analysing movement patterns from 55 participants during 3RM tests in the barbell deadlift and barbell squat as published in The Journal of Biomechanics [1] and Methods of Information in Medicine [2]. While this work focused on detecting common deviations from acceptable movement in the exercises, we noticed something interesting:

For many of the athletes the sagittal plane range of motion (ROM) of their key joint for each exercise was significantly reduced in their max-strength sets in comparison to their proceeding warm-up and sub-maximal sets.

In fact where trained practitioners were visually assessing the athlete’s technique and deeming a strength-test set as a pass, we were seeing knee ROM reductions of 15 to 50 degrees relative to warm-up and sub-maximal sets.

As we progressed our research from the lab to the field, countless sports-practitioners requested we develop a velocity-based-training module for Output Sports to aid their coaching. Additionally, they wanted something that could objectively mark the end point of a RM strength test. Whilst incredibly valuable data, we noticed the commonly used VBT target zones for ‘mean-velocity’ and ‘peak-velocity’ metrics could easily be ‘cheated’ by an athlete by reducing their ROM in a key lift. As such we wanted to create something that gave the benefits of VBT biofeedback on driving intent and moderating power during exercise whilst ensuring desired ROM is achieved rep on rep! Hence, we got our adapting our PhDs’ exercise analysis algorithms to create angular-velocity-based training (A-VBT) . This has resulted in 2 in app modules: the strength-pathway and the strength-endurance-pathway.

What Is The Strength Pathway?

Put simply, the strength pathway aims to provide the value that VBT data does [3] , but with the added assessment of ROM in the dominant limb in an exercise e.g. the thigh in a squat or the upper-arm in a bench press. This is to aid the athlete in completing an exercise with desired technique and intensity. Whilst in our PhD we used hundreds of metrics to assess compound exercise technique, to keep things actionable and interpretable for practitioners and athletes the strength pathway currently focuses on rep by rep concentric phase:

• Mean angular velocity (Degrees/second)
• Peak angular velocity (Degrees/second)
• Range of Motion (Degrees)

The Video Below Shows Such Rep By Rep Analysis As An Athlete Completes A Set Of Barbell Velocity. In This Case The Sensor Unit Is Worn On The Thigh As It Is Deemed The ‘Dominant-Limb’. On The Completion Of A Rep Where The Athlete Is Within Target Angular Velocity And ROM Ranges They Receive Positive Visual And Aural Biofeedback. If The Rep Is Not On Target, This Is Also Highlighted To The User As They Finish The Rep.

https://www.youtube.com/watch?v=b4RZWHYoLsE

Why Range Of Motion Instead Of Displacement?

We believe there is merit in both displacement and angular analysis of resistance training completion, and in fact are currently completing R&D to add valid and reliable bar-path assessment to our VBT module later this year. However, one great benefit of ROM analysis (in degrees) versus displacement (metres) is how intuitively it can be understood by an athlete and coach. Commonly, coaches cue technique with an angular value e.g. “Squat to 90 degrees” as opposed to “Squat to 60cm depth”. Using the A-VBT pathway keeps  analysis and feedback in this commonly used frame for discussing technique.

How Does Angular Velocity Relate To Linear Velocity Data?

One of the great aspects of VBT is the sheer volume of research completed in the space, providing great insights on various aspects of S&C programming with VBT. Some of this is briefly summarised in our introductory Guide to VBT here. In particular, exercise specific ‘velocity-zones’ pertaining to the force-velocity curve are a very popular way to increase the specificity of an exercise program. As such, we often get asked how does the angular velocity measurement in degrees/second relate to linear velocity measurements in metres/second.

Our initial analysis of bodyweight squat data suggests a very strong relationship between VBT and A-VBT measurements. The figure below shows over 100 reps comparing peak angular and peak linear velocities across the force-velocity curve in squats. As is evidenced from the R-value of > 0.96 the values have a strong correlation. Initial analysis suggests both a strong linear and quadratic relationship between the readings.

Correlation plot demonstrating the relationship between peak sagittal angular velocity readings from a thigh worn Output-unit to peak linear velocity readings from a barbell-positioned Output-unit.

It is our contention that the exact transform and relationship between degrees/second and metres/second may be exercise specific. Therefore, we currently recommend that for coaches to achieve a target angular velocity range for their athletes in any exercise, they observe and record 3 reps they are happy represent desired intensity and ROM and then use these reps to set subsequent targets.

Applications Of A-VBT Data

Many practitioners have begun to implement A-VBT in their practice to allow for technique and performance biofeedback. A summary of some of these are described below.

Rep Max Strength-Testing

Traditionally, objectively marking the end of a repetition max strength test can be highly challenging. How do you define when technique has broken down or is no longer acceptable? With the A-VBT pathway you can set target ROM and angular velocity targets that objectively mark an ‘acceptable’ rep for a passed strength test. When an athlete fails to hit these targets, you can objectively mark the point of failure in the strength test.

Angular velocity and ROM data from a calf-pump capacity test. Point of failure is clearly denoted when the athlete’s ROM drops below the coach’s target threshold of 38 degrees.

Objective Max-Reps Strength-Endurance Assessments

Whether it's calf-pumps, chin-ups, push-ups, bodyweight squats etc. athletes have a severe tendency to cheat on ROM when doing a max rep test. The A-VBT pathway takes the guesswork and the coach-athlete debates out of max-rep tests. You can define the minimal acceptable ROM for an exercise, and when the athlete falls below the thresholds for angular velocity and ROM you have a clear and succinct max-reps strength-endurance value. The below figure shows that after rep 14 the athlete could no longer achieve the minimum acceptable threshold of 38 degrees per rep in a calf-pump test and as such a coach and athlete can objectively mark 14 reps as the max-reps value.

Angular velocity and ROM data from a calf-pump capacity test. Point of failure is clearly denoted when the athlete’s ROM drops below the coach’s target threshold of 38 degrees.

‘Tailor-Made’ Specificity In S&C And Physio Exercise Programming

With the strength-pathway feature you can build a strong understanding of a sports-specific movement which can then be used to help programme target angular velocities and range of motion. For instance, one of our user’s is an elite rowing S&C and has used the pathway to understand target ROM and angular velocities for barbell back squats which replicate max-effort rowing. For Physio applications, we have seen pro-rugby players have their ROM and angular velocities steadily progress to symmetrical readings in exercises such as single-leg extensions and single-leg squats as they recover from knee injuries.

Understanding The Relationship Between Body-Position And Power Production - A Clear Understanding Of Sticking Points And More

Another advantage of the strength-pathway is that it allows you to gain a deep understanding of athletes’ power production throughout their movement. For instance the plot below shows back-squat data where the athlete appears to have a ‘sticking-point’ between -75 and -58 degrees of thigh orientation. Such-analyses can help you understand an athletes power production and identify ranges of weakness that can then be targeted through specific exercise programmes. Additionally, the pathway can be used to give biofeedback to an athlete to focus on generating more power in ranges where they have deficits.

Image showing sticking point/range of weakness during a repetition of barbell back squats

Take-Home Messages

The use of the common ‘mean velocity’ and ‘peak velocity’ VBT metrics in isolation will not capture when an athlete completes an exercise with sub-optimal range of motion.

The A-VBT pathway enables the benefits of VBT biofeedback whilst also adding real-time biofeedback on range of motion of the dominant limb in an exercise.

Angular velocity data strongly correlates with linear velocity data commonly used in VBT training in barbell back-squats.

Future work will investigate more exercise specific relationships between A-VBT and VBT readings.

The combination of technique and performance variables enables a vast variety of applications in S&C and Physio including:

• Objectively detecting the point of failure in rep-max strength testing.
• Objectively detecting the point of failure in max-rep strength-endurance tests.
• ‘Tailor made specificity’ for S&C with a focus on sports-specific movements.
• Assessing ROM versus power production throughout a rep to understand an athlete’s sticking-points and points of proficiency.

REFERENCES

O'Reilly, Martin A., et al. "Classification of deadlift biomechanics with wearable inertial measurement units." Journal of biomechanics 58 (2017): 155-161. https://pubmed.ncbi.nlm.nih.gov/28545824/

Whelan, Darragh F., et al. "Technology in rehabilitation: Comparing personalised and global classification methodologies in evaluating the squat exercise with wearable IMUs." Methods of Information in Medicine 56.05 (2017): 361-369. https://pubmed.ncbi.nlm.nih.gov/28612890/

Weakley, Jonathon, et al. "Velocity-Based Training: From Theory to Application." Strength & Conditioning Journal (2020). https://journals.lww.com/nsca-scj/Abstract/9000/Velocity_Based_Training__From_Theory_to.99257.aspx