Colin Griffin is a strength and conditioning coach at the Sports Surgery Clinic, where he is Clinical Lead for Foot and Ankle Rehabilitation. He also coaches a number of Irish athletes and is a Coach Education tutor with Athletics Ireland. He is currently undertaking a Ph.D., working under Professor JB Morin at the University of Côte d’Azur investigating Achilles tendinopathy rehab and lower limb biomechanics. He has undergraduate degrees from University of Limerick and Setanta College, and a master’s degree from University College Dublin. Colin has been working at the Sports Surgery Clinic since 2014, before which he enjoyed a long career in elite sport where he competed at two Olympic Games (2008 and 2012) and World and European Championships in the 50km walk. Since retiring from competitive sport in 2014, he has been running to maintain fitness with a marathon PB of 2.23.00 posted in 2019.
Freelap USA: The soleus is starting to get more attention now with sonography and biomechanical research. While the morphological changes are clear with distance athletes, sprinters have less attention in the research world. How can soleus strength training potentially help speed and power athletes? Any conjectures?
Colin Griffin: I think it is important to consider the anatomy and physiology of the soleus muscle. It is a high-force muscle with the largest physiological cross-sectional area of the calf muscle complex1 and composed of mostly type I oxidative fibers enabling high work capacity2. The architecture of the soleus muscles and its slow shortening velocity are suited to minimizing energetic cost during running.3 With short fascicle lengths, it has a very narrow region on its force-length curve where force is maximized during maximal speed and distance running. Tendon mechanical properties will also influence muscle contractile conditions.4
The role of the soleus in sprint performance appears to be distinctly important during acceleration. Lai’s modeling study in 2016 showed that there is more positive muscle fascicle work generated by the soleus in the first few foot contacts during acceleration.5 This may be due to the active dorsiflexion that occurs prior to footstrike during early acceleration while the knee is more flexed, meaning that the soleus muscle-tendon unit is pre-tensioned. This pre-tensioning facilitates greater muscle fascicle excursions and shortening velocities, and thus more elastic strain energy is applied to the Achilles tendon with a more amplified energy return. Also, ground contact times are higher during the early acceleration phase, enabling more time for the soleus fascicles to operate at their optimal force-length-velocity region to maximize its force capacity.
We are beginning to understand more about muscle architectural gearing in pennate muscles. This is where, during high-velocity muscle contractions, the muscle fascicles rotate, causing a bulging of the muscle belly, and the muscle shortens more than the muscle fascicles.6 This might also be important for speed and power athletes to limit the amount of fascicle shortening so that force generation is maximized. I’m also interested to explore the potential role the central tendon that runs through the anterior compartment has in explosive contractions.
With athletes, for whom acceleration or lower limb explosive qualities from knee-flexed positions are important, I believe it is worthwhile to focus on maximizing force capacity from the soleus and to target explosiveness through isometric or heavy concentric exercises with maximum intent. Heavy-resisted sled acceleration drills may have a role to play here.
In field sport performance aside from acceleration, there are many reasons why soleus strength is important. It provides the largest contribution to vertical support during the stance phase of running and during side-step cutting.7,8 It also has a significant role in controlling tibiofemoral shear forces and opposing knee valgus and rotational moments during landing.9 Dorn’s 2012 paper, which has been widely cited, showed that the soleus operates closer to its maximal force capacity even at jogging speeds, compared to other lower limb muscles. Training its metabolic properties as well as force capacity can help players in field sports become more fatigue-resistant by using less of its muscle force capacity at low-intensity running or jogging.Training the soleus’s metabolic properties as well as force capacity can help players in field sports become more fatigue-resistant, says @colingriffin. Click To Tweet
Even though the soleus is part of the triceps surae muscle group, its timing and pattern of recruitment can differ from the gastrocnemii depending on the task.10 During early stance phase, it appears to have a stronger neuromechanical relationship with the vasti muscles than it does with the gastrocnemii.11 There may be a strong case to target the soleus in isolation (in knee flexion) depending on the athlete’s needs and the demands of their sport.
I would test soleus isometric force capacity in a flexed knee position on the force plates as well as total plantar flexor peak force in a standing straight leg position. This gives me an idea of soleus contribution to total plantar flexor peak force and helps guide my programming. We would aim for more than twice body weight as a good measure of relative peak force in a single-leg seated calf isometric test.
Freelap USA: Achilles injuries are growing in the NFL, and many coaches are interested in strength training concepts that are practical and time effective. Any ideas on eccentric training for this population?
Colin Griffin: There are many intrinsic and extrinsic risk factors for developing tendon injuries that may require a more individualized approach for each athlete. An athlete who has had a previous Achilles or calf injury is certainly at a higher risk and needs a more tailored program. Heavy calf loading, regardless of contraction type, seems to favor an increase in tendon mechanical properties.12
The high force applied with slow muscle contractions and optimal tendon strain provides a strong mechanical signal to the cells to trigger a biochemical response resulting in improved tendon matrix properties. Heavy isometrics or supramaximal eccentrics have the strongest evidence for increasing tendon stiffness (tendon’s resistance to the force applied) and Young’s modulus (stiffness normalized to tendon cross-sectional area and dimensions) within 4-8 weeks.13,14 You can periodize this type of work throughout the season with some front loading during the pre-season followed by in-season microdosing.
There has been plenty of debate in recent years about the role sustained isometric contractions have on pain modulation in tendons. I find that some athletes subjectively respond well to them and would include these as part of their warm-up before running-based sessions.The future direction for managing Achilles tendon injuries may be the utilization of monitoring tools and assessments throughout the season, says @colingriffin. Click To Tweet
The future direction for managing Achilles tendon injuries may be the utilization of monitoring tools and assessments throughout the season. There is some good evidence for using ultrasound tissue characterization (UTC) to screen tendons for changes in echo types. Type I echo types indicate healthy aligned tendon fascicle bundles, and a greater proportional increase of type II, II, and IV echo types, respectively, indicate pathological changes.15 However, pathology on imaging does not always indicate injury or pain but could suggest acute remodeling occurring within the tendon, indicating the need for appropriate training interventions or recovery.
It would also be useful to have a convenient but accurate way of measuring tendon stiffness so that you can determine how much plantar flexor force is required to achieve an optimal level of strain (4%-6%) for favorable tendon adaptations.16 The most accurate way is with isometric contractions on an isokinetic machine using real-time ultrasound, where you calculate Achilles tendon force and strain while correcting for rotations of the heel. This may overestimate tendon strain and contributions from the dorsiflexors, which may overestimate plantar flexor torque. But this is time-consuming and requires a lot of data processing.
Convenient methods such as shear wave elastography have their limitations for accurately measuring mechanical properties of tendon tissue. Finally, it is important to consider the variable morphological features of the soleus, medial, and lateral gastrocnemii, as well as the degree of twisting of the sub-tendon fascicles as they form the Achilles tendon, as the different muscle contributions can impact the orientation of tendon strain.17
Freelap USA: Let’s talk about surfaces and injuries. Tibial shock is higher with grass running, and pretension or activation is higher with harder surfaces. Those aforementioned details make return to play very difficult to decide on for some professionals. How do you sequence training or structure training better so athletes can use the different surfaces more effectively in rehab or recovery training?
Colin Griffin: This is a topic that interests me, as I regularly treat runners who have suffered a tibial stress injury. The traditional belief was that such injuries were caused by “pounding the pavement,” and early evidence suggested that a high loading rate on the initial peak of the vertical ground reaction force curve was a risk factor. Recent work points us in the direction of bone stress injuries caused by mechanical fatigue18, and that muscle contractions increase bone loading more-so than vertical loading rate19.In terms of training surface, I am more convinced that it is the adjustment to a different surface while training loads remain constant that can be problematic, says @colingriffin. Click To Tweet
In terms of training surface, I am more convinced that it is the adjustment to a different surface while training loads remain constant that can be problematic. The same could be said for changing footwear. Muscle and joint coordination patterns change as they adjust to the new surface20, and it may be that muscles either increase in activation, resulting in higher bone loads, or experience earlier onset of fatigue, resulting in higher bone shocks—or a combination of both, which may be the perfect storm for bone stress injuries. In field sports, this can be an issue throughout the season where weather and ground surface conditions change, or athletes switch to or from training on an AstroTurf pitch. In track and field, the biggest challenge I see is during springtime, when more high-intensity track sessions are done in spikes.
The use of wearables such as inertial measurement units (IMUs) may help control some of the risk factors for bone stress injuries. I have one good case study of a runner with a history of tibial stress fractures who wore iMeasureU’s IMU Step device for four weeks. We also assessed his ankle isokinetic strength and reactive strength, and we identified deficits on his injured side.
During that period, he developed medial tibial pain symptoms on one particular run. We were able to track his bone stimulus (using iMeasureU’s algorithm, which includes tibial shock and number of steps) for each training session, and his injured side always showed a functional asymmetry. However, in the days preceding his flare-up and following a plyometric session, his injured side had a symmetrical bone stimulus that we attributed to a potentiation response to a plyometric training session. In the subsequent days, he experienced the flare-up on a longer run.
We were able to use that feedback to infer that his injured limb was not adapted to that new symmetrical bone stimulus and advised a longer recovery window when we observed an increase in bone loading on that limb. In the final week of the four-week case study, he displayed symmetrical bone stimulus and has not experienced symptoms since. Based on my experience with this particular case study, and even though training surface wasn’t the issue, I believe you could use IMUs to monitor bone stimulus in response to a change in surface and adjust training loads and recovery windows accordingly.
Freelap USA: Plyometrics can be great for some athletes but a bane for others. How do you individualize plyometrics in training outside of technique ability? It seems that group training has lowered the standard in tailoring jump training.
Colin Griffin: I think it comes back to the type of athlete you are dealing with and the common classification of “pushers” and “pullers,” as well as the many nuances along that spectrum. Many coaches would report that athletes who rely more on their elastic qualities don’t always respond well when a focus on maximal strength is introduced too abruptly. The same could be said for athletes who rely on their high force capabilities but possess limited reactive strength qualities.
I think it’s important to understand the profile of the athlete and the demands of their sport. While it’s tempting to go all in on improving their “weak” areas, it is important not to lose sight of the athletic qualities that have made them successful in the first place.
If you were to profile a group using a reactive strength assessment (drop jump, 10-5, or any other hop test), and you see those athletes in the lower quartile of RSI scores that you want to improve, the first step is to figure out their limiting factor. Is it that they need more time on the ground for impulse? Do they have poor tendon stiffness? Is it a muscle contractile issue? Or is it poor skill or coordination? If somebody performs a drop jump from a 30-centimeter box and they can’t rebound anywhere close to that height in return, even after slightly manipulating contact time, we need to be careful. Their muscle-tendon units may not have the capabilities to handle high eccentric forces and to properly utilize tendon elastic strain energy.Aside from looking at RSI numbers, I also look at the shape of the vertical ground reaction force curve, says @colingriffin. Click To Tweet
Aside from looking at numbers, I also look at the shape of the vertical ground reaction force curve. From examining foot contact patterns, a smooth line indicates good ankle joint stiffness when we cue active dorsiflexion prior to initial contact. A fluctuation in the line often coincides with landing passively in plantarflexion and demonstrating poor ankle stiffness. I find that this can be changed when we retest after giving the athlete feedback and cueing them.
For field sport players possessing high muscle mass (we typically see some in rugby or Gaelic sports players in Ireland), the use of band assistance may help to fine-tune the skills necessary to improve their reactive strength. I also focus on basic coordination patterns in skipping and “ankling” drills before progressing on to pogo hops, drop jumps, and more advanced exercises. I focus on good alignment during ground contact (ankle, knees, and hips vertically stacked with good lumbo-pelvic control) and watch for those who rely on early “tucking” during the flight phase.
Some of these finer details can be missed in a group setting. Some athletes may need to spend more time working on calf strength exercises to condition the muscle-tendon unit for plyometric loads. Tendon stiffness is important for plyometric performance, as it influences contact time and jump height.21,22
Either way, I think improving reactive strength is time well spent from both a performance and injury perspective. Injuries such as ACL rupture or ankle ligament sprains occur in less than 100 milliseconds, which is too late for muscles to produce enough force in response to ground contact. Therefore pre-activation prior to foot strike is key, and joint stiffness and reactive strength are closely linked with early-phase rate of force development. However, for athletes with limited or no training history with plyometric training, a long-term approach may need to be introduced and progressed safely.
Freelap USA: Barefoot training is still a thing—what are your thoughts on manipulating the use of time without shoes? It seems it could be problematic for some but useful for those looking for selective strength training below the knee.
Colin Griffin: In the running world, we have witnessed a big pendulum swing in the last 10 years or so, influenced by the book Born to Run. This promoted the concept of barefoot running or minimalist footwear, as that’s what we were naturally adapted for based on our hominid ancestors. Then we had a large number of injuries experienced by people who made that switch!
I believe there is a place for barefoot training, and I certainly encourage athletes to do some drills, short runs, and strength exercises barefoot. One of my go-to calf strength exercises is always done barefoot, where I emphasize foot positioning, rearfoot control, and loading through the first MTP joint to promote recruitment of the foot’s intrinsic and extrinsic muscles, as well as developing calf strength. But barefoot exercise may not be advisable for an athlete with conditions such as sesamoiditis, plantar plate injury, or hallux rigidus.
So, it depends on the athlete and what you are trying to achieve, as well as getting the loading right. There is a time and a place for many interventions, even if they seem a little extreme!
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