Still Think It's The Thigh Muscles?

I have seen many patients who have had an anterior cruciate ligament (ACL) tear over the years.  Some patients chose not to go under the knife but most had reconstruction done. ALL of them were taught to focus their strengthening on their quadriceps (or thigh) muscles.

So not surprising that a recently published study by Alzobi et al (2026) found that patients who did not opt for surgery exhibited progressive hamstring muscle atrophy.

A total of 1,207 thighs were examined. There were 92 with ACL tears and the other 1,115 acted as controls. The average age of the subject group was 61± 9 years.

Over 4 years, the ACL deficit thighs were smaller by an average of 28.18 mm, all due to progressive hamstring atrophy. The differences ranged from 13.92 to 42.43 mm smaller. The sartorius muscle also atrophied by an average of 3.02 mm.

There were no significant differences in the quadriceps or adductor cross sectional area. hamstring force was decreased significantly whereas quadriceps force showed no significant change.

The researchers concluded that muscle deterioration occurred in the posterior thigh muscles (hamstrings) with minimal changes in the front thigh muscles (quadriceps) over time. And for ACL deficient knees, it is really important to target long term rehabilitation strategies focusing on hamstring preservation. 

We already know that one of the reasons women sustained ACL tears is that their hamstrings were significantly weaker than their quadriceps muscle strength.

If you have been reading our previous blog articles, you already know that the quadriceps (thigh muscles) and gastrocnemius (calf muscles) increases load on the ACL due to anterior shearing forces at the tibia (shin bone). This is especially so when the knee is straightened (Maniar et al, 2022).

The hamstrings and soleus (deeper calf muscles) help to unload the ACL by generating posterior tibial shearing forces (Maniar et al, 2022).

So for those of you who have torn your ACL, whether or not you choose to go for surgery, make sure you focus on your hamstrings and soleus muscles instead.

References

Alzobi O, Mohajer B, Fleuriscar J et al (2026). Thigh Muscle Changes In The ACL-Deficient Knee: A 4-Year Lonitudinal MRI Study of 1,207 Patients. JBJS Am. 108(3): 219-226. DOI: 10.2106/JBJS.25.0064

Maniar N, Cole MH, Bryant AL et al (2022). Muscle Force Contributions To Anterior Cruciate Ligament Loading Sports Med. DOI: 10.1007/s40279-022-016743

Carbon Plated Running Shoes Improve Running Economy

Picture from Runrepeat.com

Remember my post on whether super running shoes work or whether it was just a placebo, especially for recreational runners?  Well, for serious runners they definitely make one run faster. 

In theory, the super shoes reduces your energy cost when you run, making runners more efficient at the same running speed.

How do they actually make you run faster? In my past versus present post, I highlighted how super highly stacked midsoles, super responsive PEBA foam, and uppers are optimized biomechanically. In addition, the carbon plates offer runners with energy return on every stride. The propulsion and fit designed to minimize fatigue over the whole marathon distance, almost like pushing off, off a trampoline when you run.

However, what if one ran in carbon plated running shoes versus shoes that did not have a carbon plate? That was what a new systematic review investigated, how much lower the energy cost is when you compare running in carbon plated versus non carbon plated shoes and how big the effect was.

14 studies pooled by researchers to compare carbon plated versus non carbon plated shoes when running (Kobayashi et al, 2026). Each runner in all the studies ran in both types of shoes to minimize 'between-runner" variability.

The results showed that the carbon plated shoes significantly lowered metabolic cost (or energy cost) for all the variables measured. Running economy, oxygen consumption and energetic cost of transport (ECOT)  all favoured the carbon plated running shoes.

Here's what the researchers summarized that was interesting. The carbon plated shoes lowered metabolic demand during running by 2 to 3 percent on average. This means that the total amount of energy and oxygen required by the body to sustain cardiovascular function, muscle demands and heat regulation while running was less in the carbon plated shoes.

This matches what runners "feel" in super shoes. Not a night and day transformation but definitely a sufficient edge, more so when pace increases and race distances get longer. (Recap: runners were only running 6 minutes at 10 km/h pace in the super shoes or super placebo post).

So if you are still deciding on buying carbon plated super shoes for your next attempt to beat your 10km/ 21km/ marathon, (or insert your distance) personal best, the scientific answer is a definite yes. Especially if you are not a beginner and can afford them.

Reference

Kobayashi EN, Toledo RRF, de Almeida MO et al (2026). Metabolic Effects Of Carbon-Plated Running Shoes: A Systematic Review And Meta-Analysis. Front Sports Act Living. 9(7): 1710224. DOI: 10.3389/fspor.2025.1710224

What Is The Right Way To Train?

ST 040226

Controversial topic this week everyone. Earlier in the week (4/2/26), there was an article in the Life section of the Straits Times on page C3 with the headline "You can get away with minimum exercise". It was originally published in the New York Times on 150126.

And you often see such headlines in Tik Tok, X or Facebook. When such a study, article, post or reel does well, the exercise scientists, coaches, influencers comment to critique, nitpick or praise the wording, arguing that the study, article, post or reel is being "oversold" or interpreted wrongly.

Are these exercise scientists, coaches, fitness influencers and keyboard warriors just argumentative or is it something else? The above mentioned groups will never see eye to eye. And that is fine since we all learn or at least get entertained by them (pictured above and below).

I think they are disagreeing about different things. "Training" is thought to be the same for everyone. It actually isn't.

When a coach or exercise scientist (or physiologist) talks about training, they are referring to training for sporting performance, or a race. A 40 km cycling time trial, a marathon, a 10 km race or a Hyrox competition. There is an objective measure, or the outcome has a clear definition of who is first or second.

When a fitness or health influencer talks about training, they are not talking about training for a race or competition, they are referring to wellness, losing weight, longevity, reducing falls and perhaps looking or feeling good. It does not require one to revolve their whole life around exercise, training and competing.

Is exercise just exercise? Both their perspectives overlap. Health focused training can improve performance. Training for performance improves health, until you overtrain, which then can be harmful.

However, the time constraints and success metrics are totally different. If one does not say which you are referring to (health or performance), then that's when you will have both sides disagreeing passionately when they are in fact talking about 2 different things.

The exercise physiologists and coaches will treat the study as giving instructions for how to train like an athlete. The fitness influencers will translate it into something the average person can understand and apply. 

Same data, different interpretation.

Remember my article about Zone 2 training? The endurance coaches and exercise physiologists will get their athletes to train easy mostly in Zone 1 or 2. Build the aerobic base. Then 10-15 percent of high intensity work. Are they correct? Definitely. If their athletes are training in excess of 20 plus hours a week, they cannot go hard all the time. They will get burned out and most likely injured.

The fitness influencers are advising humans and mere mortals who are maybe exercising just once or twice a week, definitely under 5 hours total. They are not deciding whether to train at altitude or to periodize their training. They are probably trying to find time and convince themselves to exercise after a long day at work. 

So when they read or watch online reels about exercising mostly at Zone 2, they will think they need to devote a LOT of time exercising at low intensity.

For the athlete, that's super sensible. For the mere mortal and weekend warrior with limited time and motivation, it is impractical or even impossible.  Not because Zone 2 is bad. For Zone 2 to work, you have to accumulate hours. To have super powers, you have to put in the hours.

This is why Zone 2 versus HIIT (high intensity interval training) arguments get so heated. The 2 sides are debating 2 completely different cases but using the SAME lingo and assume that studies on athletes apply to studies on the average population and vice versa.

Studies on interval training, HIIT etc to improve VO2 max are designed to be time efficient. All the research says that if someone has limited time, what is the smallest dose of exercise that gives meaningful results? Or like the picture I posted on top "You can get away with minimum exercise".

If you do not have enough time, you need higher intensity training to provide a stimulus that is large enough to make a difference. This is why the coaches give their 2 cents worth and say that HIIT alone will not prepare you for a marathon.

The coaches are correct, but the fitness influencers were also not getting their readers to race marathons. A study that shows HIIT improves VO2 max does not automatically become a training plan for a marathon even though it is about aerobic fitness. 

Here is what confuses everyone, myself included sometimes. When we take research designed for the elite athletes and try to apply it to the general population and vice versa. Then we act surprised when different groups object for different reasons.

A 6 hour easy ride for a Tour De France rider is simply not normal, realistic, nor repeatable and effective for a weekend cyclist given the time and motivation they have. Remember my 160 km ride to Kukup, it took me almost half a day to recover.

The problem is we cannot communicate on the same wavelength when it comes to exercise. There are disagreements because we keep failing to clarify the context.

So if you are just exercising for general health and do not have plenty of time and motivation, high intensity training will be time efficient for improving your aerobic fitness, metabolic health and help you live longer. Not because easy training is useless, but you are trying to get meaningful adaptation out of limited time.

For athletes and those who have time to accumulate volume, Zone 2 exercise is sustainable, easier to recover from and foundational. It becomes really powerful as Zone 2's super power is accumulation. It improves durability, helps support overall training volume and makes you better at endurance and also to handle the high intensity training when you need to.

Coaches can tell you how their athletes build great endurance while not being helpful for the average Joe or Jane whose main goal is getting started. 

Fitness or health influencers can be correct about time efficient fitness strategies while being totally inadequate with regards to an athlete's performance in a specific sport.

An exercise physiologist and sports scientist can be super accurate about what a study shows but missing how the lay person will interpret it in the real world.

I hope this explains things better so we know that there is no one 'best' way to achieve fitness, health or performance goals.

How Much Running Is Too Much?

I had a patient earlier this week who's an ultra runner. She did an ultra race in December last year and then took 3 weeks off running. Her first run back was a 20 km run and she started having left knee pain since.

I told her about an interesting article I read last week about the "single-session paradigm" for running injuries (Frandsen et al, 2025). 

The study tracked 5,205 runners over 18 months. Their average age was 46 years and 22 percent of the runners were females. The runners accumulated 588,071 run sessions via the Garmin GPS watches during the study period. The researchers were interested in self reported running related overuse injuries rather than traumatic injuries.

The runners were categorized into training load "spike" states. If mileage was <  10 percent increase, it was categorized as regression. A small spike would be greater than 10 but less than 30 percent increase. A moderate spike would be greater than 30 percent but less than 100 percent while a large spike would be greater than 100 percent increase.

Weekly changes in mileage using acute : chronic workload ratio (ACWR) - 1 week versus past 3 weeks. Week to week ratio, that is change from week to week were also analyzed.

For the ACWR (weekly changes) and week to week ratio, the study did not find any clear positive association with injury. In fact in some runners, a "negative dose response" was observed meaning a higher ACWR did not always mean more injury.

They found that when there was a spike in running mileage in a single session (rather than a gradual weekly increase relative to the longest run in the previous 30 days, many injuries occurred. This was named a shift to a "single-session paradigm" for running injuries.

This matches exactly with how my patient was injured. No running for 3 weeks, then in her first run back she had her longest run in the past month. The body needs time to adapt, big increases in mileage overloaded her muscles, bones, ligaments and connective tissues.

Please note that this study had runners who self reported their injuries, they were not diagnosed, so we need to be cautious and sensible when interpreting the results. Please do not think 'never increase mileage', it is more about progressing and moderating.

Those of you who are wearing smart watches, other tech devices and perhaps using Strava, note that this study suggests that algorithms that measure your weekly mileage load rations (or ACWR) may be under calculating risk. Your devices may need to include "single session spike" metrics or at least be able to compare with longest session in the last month.

Whether you train under a coach or are self coached, plan sessions so that large increases in distances are avoided. Or make sure you monitor carefully and plan extra recovery. Do not just tally weekly mileage, look at how the session distances compare to your maximum long run in the past month. Monitor your "David Goggins /monster sessions" that deviate from your regular training.

The average mean age of the runners was 46 and 76 percent were male. Younger athletes and elite athletes may be different. Other than distance, I will also include running pace, prior fatigue levels, surface of run and shoes to be monitored.

For healthcare professionals working with ultra runners, you can educate them about the single session spikes having higher risk than weekly totals, like I did with my patient. Ask them in detail about their training regime and pay close attention to the longest run in the recent 30 day window.

Reference

Schuster Brant Frandsen J, Hlme A, Parner ET et al (2025). How Much Running Is Too Much? Identifying High-Risk Running Sessions In A 5200-Person Cohort Study? BJSM. 59 (17): 1203-1210. DOI: 10.1136/bjsports-2024-109380