Is more muscle activation good or bad in sport?

[Ina Janssen]

Dear Biomech-L members,

We are using shorts embedded with electrodes (Mbody) to try and get an insight into muscle activation during elite sport (sprinting, cycling, competition). These shorts give a % of muscle activation when comparing the left and right muscles groups (quadriceps and hamstrings; they do not discriminate between individual muscles).

We have been piloting the shorts and have noticed that with some athletes there is 15-20% difference in hamstring (for running) and quadriceps (for cycling) activation. Now our question is whether more activation is good (although we know that more does not mean stronger...) or whether is it bad (more activation required to produce the same movement).

We are planning on using the shorts during isokinetic testing to try and make a link between activation and strength. Meanwhile, does anyone have any thoughts on whether there is a clinical cut off to asymmetry (such as often noted in isokinetic testing) and whether more activation is good or bad?

Thanks in advance!

Kind Regards,
Ina Janssen

Sport Biomechanist
Netherlands Olympic Committee
ina.janssen@nocnsf.nl

[Jack Winters]

Re: Is more muscle activation good or bad in sport?

Hi Ina,

Several comments, based mostly on insights from past muscle modeling work, but also personal interests in triathlon/rowing. First, a small one: an EMG excitation signal is not quite the same as muscle activation. That said, for the types of tasks you mention I think it is both good and bad, and it depends especially on timing issues.

Let's view EMG as related to expressing sculpted neuromotor control action (sometimes called excitation) and muscle activation as calcium-binding to troponin. When a muscle needs to be used, high and quick EMG control and muscle activation is advantageous, and of course has to be balanced by the "cost" especially of recruiting fast muscle fibers (and the associated fatigue issues) - hence running and cycling EMGs should be different in shape and magnitude. But perhaps even more importantly, muscle sensitivity analysis suggests that rapid and well-timed EMG decreases that help sculpt rapid muscle deactivation is also very (very!) important. This includes the obvious stretch-shortening use, but also other contexts - partially-activated lengthening muscles can generate forces that can be a big drain on propulsive performance. A muscle that cannot deactivate quickly puts an athlete at a considerable disadvantage, and I personally believe helps distinguish great-performing athletes from good-performing athletes. For instance, the great basketball player performing jumps and cuts needs to get muscles turned off very quickly. This implies not only exquisite neuromotor control and muscle strength/power capacity, but also an SR lattice network with a high density of (ATP-consuming) SERCA pumps so that Ca++ deactivation is as fast and effective as possible (and ditto for axonal Na/K etc pumps, but less an issue). A well-aligned muscle architecture including a high density of local SERCA pumps (and mitochondrial lattice) is a thing of beauty, making EMG transient signals more effective. Also, a fatiguing athlete likely has trouble with both transiently activating and deactivating of muscle.

Hope this is helpful,
Jack

Dear Biomech-L members,

We are using shorts embedded with electrodes (Mbody) to try and get an insight into muscle activation during elite sport (sprinting, cycling, competition). These shorts give a % of muscle activation when comparing the left and right muscles groups (quadriceps and hamstrings; they do not discriminate between individual muscles).

We have been piloting the shorts and have noticed that with some athletes there is 15-20% difference in hamstring (for running) and quadriceps (for cycling) activation. Now our question is whether more activation is good (although we know that more does not mean stronger...) or whether is it bad (more activation required to produce the same movement).

We are planning on using the shorts during isokinetic testing to try and make a link between activation and strength. Meanwhile, does anyone have any thoughts on whether there is a clinical cut off to asymmetry (such as often noted in isokinetic testing) and whether more activation is good or bad?

Thanks in advance!

Kind Regards,
Ina Janssen

Sport Biomechanist
Netherlands Olympic Committee
ina.janssen@nocnsf.nl

[Ina Janssen]

Re: Is more muscle activation good or bad in sport?

Many thanks to those who replied through this thread and directly! It looks like a topic that still needs some discussion..