Do You Have More Slow Or Fast Twitch Muscle Fibers?

Picture from Bodyworksprime

I always knew I had some decent fast twitch muscle fibers in me. How do I know you may ask? I could always sprint at the end of a race. That's how I won most of the track races I took part in while competing in school competitions. My strategy was always to sit and wait off the leader's shoulder until the last 80-100 m and outkick whoever was there.

So I was very surprised when a newly published paper (Lievens et al, 2024) suggested that only 50 percent of elite coaches and sports scientists (out of > 400) actually know whether their athletes have slow-twitch or fast-twitch muscle fibers. Yet 90 percent of them believe that knowing the dominant muscle fiber type of an athlete is useful for optimizing training and performance.

Humans on average have a roughly 50-50 mix of slow and fast twitch fibers. There can be a huge variation around this average as some people can be mostly slow-twitch while others can be mostly fast-twitch. I have written in more detail about the 3 different types of muscle fibers we have. 

Here is a quick recap. Type I or slow twitch muscle fibers which are the smallest and produce the least amount of forces, but once trained can go all day long without fatiguing. They also help to hold and stabilize our posture.

Type II or fast twitch muscle fibers which are further divided into Type IIa and Type IIx (also known as IIb). These are larger muscle fibers and produce a greater and quicker force (than type I), but have less mitochondria, myoglobin and capillaries (compared to Type I) and are prone to fatigue quicker.

Type IIa (also known as intermediate muscle fibers) is a mixture of Type I and IIx fibers. They use both aerobic and anaerobic energy systems and fatigue slower than Type IIx. Proper training of Type IIa fibers will increase their ability to utilize aerobic energy, translating to greater endurance.

Type IIx are the largest muscle fibers and produces the most forces but are inefficient and fatigue quickly as it has low oxidative capacity and relies on anaerobic energy.

If you have read this far, you may already know more about muscle fibers than 50 percent of the coaches in the article above.

Studies have shown that those with more fast-twitch muscles have a faster last lap sprint in the 1500 m while those with more slow-twitch fibers generally do better in races when they are more evenly paced.

Another study (Swinnen et al, 2024) showed that those with slow-twitch fibers tend to have better running economy (use less energy at a given pace) since slow-twitch fibers uses less energy than fast-twitch fibers. 

The gold standard to know your fiber type is a muscle biopsy which means taking a small piece of your muscle for analysis. It is a really painful process plus who wants to give away hard earned muscle?

That is probably why the coaches surveyed in the Lievens et al (2024) study said they do not know their athletes' fiber type, especially if they coach middle distance, team sport athletes or recreational athletes who were not active previously. 

Coaches in the Lievens (2024) study relied heavily on how high you can jump (or how long you stay in the air). It is a decent proxy for fast twitch muscle fiber testing. Men with a vertical jump in excess of 50 cm (20 inches) and women 35 cm (14 inches) have predominantly more fast-twitch fibers.

Another study found that fast-twitchers can usually do 5-8 reps at a given load (80 max in the study), while slow-twitchers did 11-15 reps. About a third in the study group did 9-10 reps and they had an even mix of fast and slow twitch fibers. Those with more fast-twitch fibers tend to be stronger but note that they fatigue more quickly too.

This has implications for strength training since the 1-rep max calculations used to find how many reps to do at a lower weight will be different for fast versus slow twitch fiber types. Slow twitchers need to do more reps to get a comparable stimulus.

Perhaps a good estimate is how you fare over long versus short distances. Note that it will be affected by factors like how you have trained. This is definitely worth considering when you are deciding what races to compete in or how many reps to do while lifting. 

What muscle fibers you have is not destiny and does not have to determine your athletic goals. It may tell you the best way to get there.

Reference

Lievens E, Van de Casteele F, De Block F et al (02024). Estimating Muscle Fiber-Type Composition In Elite Athletes: A Survey On Current Practices And Perceived Merit. Int J Sp Physiol Perform. 19(11): 1197-1208. DOI: 10.1123/ijspp.2024-0043

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Cardio Before Or After You Lift Weights?

Picture from Diamondback Fitness

Last week's post was about weekend warriors, who did not have enough time to exercise during weekdays. My patient who read that post was asking me if she should lift weights or do cardio first if she wanted to do both back to back. I told her it depends on her athletic goals and how much time she can spare working out. 

So should you lift weights first or cardio (or aerobic training) first?

I suggested weight training first followed by cardio (or aerobic exercises). Weight training involves external loading with barbells, weights, kettlebells and resistance bands and has a more acute injury risk if already tired. Especially after a longer aerobic session, your muscles are fatigued and lifting weights after that will elevate your injury risk.

One would usually not be able to lift as much or perform that many reps compared to starting with strength training. Especially if you decide to lift heavier weights.You will definitely do a better job if your muscles are fresh.

Note that if you lift weights before your aerobic exercise it will also inhibit your aerobic performance. Research shows that there will be a reduction in speed, power and stamina. 

Actually when I used to race triathlons, I would often do weight training and then cycle and/ or run after (brick training). I'll be fatigued after the weight training which is the state I would be in after swimming and cycling before attempting the run section anyway. So that made sense for me to always run when I'm already tired to simulate race conditions. 

Lifting weights prior to aerobic exercise will not significantly increase your risk of injury compared to tackling heavy weights when you are already tired. Do aerobic training and weight training on different days to optimize both if you have time. If you are thinking of doing both, go with weight training first.

An exception to the rule for this would be the warm up. Warming up with a bit of light cardio (stationary bike or elliptical etc) prior to weight training (or any other workout) will help prime your muscles, increase blood flow, get your mental focus and nervous system ready for action. 

You can work both strength and cardio simultanesously in the same workout when you perform circuit training or HIIT as it is now commonly called. By minimizing your rest time and prioritizing your work efforts, your heart rate remains elevated while working your muscles to simulate hypertrophy. 

You do get the best of both worlds, burning calories and endurance boosting of aerobic conditioning and the muscle building and power from strength training. Just do not do them every day as your body will not have time to recover sufficiently between sessions.

Reference

Conceicao M, Cadore EL, Gonzalez-Izal M et al (2014). Strength Training Prior To Endurance Exercise: Impact On Neuromuscular System, Endurance Performance And Cardiorespiratory Responses. J Hum Kinet. 30(44) : 171-181. DOI: 10.2478/hukin-2014-0123

Are You A Weekend Warrior?

Picure from DetailingWiki

My patient and his wife were asking me about my exercise routine and they were surprised when I told them that I still exercise 6 days a week, with one total rest day. 

I'm guessing they do not know about my training routine when I was still competing. They were saying that they found it really difficult to exercise during the weekdays. They ususally only found time on the weekend to exercise.

I told them to fret not as fitting in their exercise on weekends will still reap significant health and survival benefits as well as help their brain health.

Findings from an earlier large study (64,000 subjects) showed that people who pack all of their exercise into 1 or 2 days of the week (often referred to as weekend warriors) appear to lower their risk of dying about as much as people who exercised 3 times a week or more (O' Donovan et al, 2017).

Another recent study (August 2024) showed that a weekend warrior who met physical activity guidelines had similarly lower risks of dementia, stroke, Parkinson's disease, depressive disorders and anxiety compared to a more regular activity pattern (Min et al, 2024). Physical activity guidelines are mor than 150 minutes of moderate intensity exercise per week. 

This study by Min et al (2024) included 75, 629 participants. Their findings highlight that this is an alternative for those who are unable to exercise more regularly during the week days. 

Go and be active whenever you can

For those of you are are struggling to fit in any exercise during the week, remember that any activity is worthwhile, even if it is just on the weekend.

References

Min J, Cao Z, Duan T et al (2024). Accelerometer-Derived "Weekend Warrior" Physical Activity pattern And Brain Health. Nat Aging. 4: 1394-1402. DOI: 10.1038/s43587-024-00688-y

O' Donovan G, Lee I, Hamer M et al (2017).Association Of "Weekend Warrior" And Other Time Physical Activity Patterns With Risks For All-cause, Cardiovascular Disease, And Cancer Mortality. JAMA Int Med.177(3): 335-342. DOI: 10.1001/jamainternmed.2016.8014

New Study Does Not Recommend Standing Desks

Picture from CMD

I have written previously on the ill effects of sitting and prolonged sitting. This has also led to the phrase that "sitting is the new smoking". Which subsequently led to standing desks as a 'trendy' option to offer a way to reduce sitting time.

Previously, some of my patients have also asked me to write a memo for them so they can get  their company to pay for a standing desk at work, while other patients have simply asked for my opinion.

My take on standing desks then? I've seen many of my patients go straight from sitting to a standing desk get different problems. Being unaccustomed on their feet all day long posed new risks. It can inhibit proper circulation and add additional pressure to your legs, hips and lower back. Sort of like jumping from the frying pan into the fire if you ask me.

My suggestions for these patients was not to switch to a standing desk for the full work day, especially if they have been sitting all day immediately. To make sure they gradually phase it in.

Like previous ergonomic chairs, desks etc, there hasn't been much evidence supporting the benefits of standing desks. The earlier limited studies did not comprehensively assess long term health consequences.

In a newly published study this month (Ahmadi et al, 2024), 83, 013 participants wore devices for up to 7 years to track their sitting, standing and physical activities. This was more accurate and objective than self reporting by subjects. The researchers found that sitting for more than 10 hours a day was associated with a higher risk of heart disease and stroke.

The researchers also found that standing more did not mitigate this risk of stroke and heart disease. In fact standing for extended periods was linked to a increased risk of circulatory problems. This suggested that simply changing from stationary sitting to standing will not solve the problem since our bodies respond better to movement rather than staying in static positions. Remember motion is lotion.

Workplace interventions that promote movement found that office workers who reduce sitting time by adding light walking and standing had improvements in blood sugar levels.

So, walk to your colleague to talk to them instead of calling or emailing, take the stairs often instead of elevators, walking to the pantry etc all contribute. Better still if you can do 10 bodyweight squats every 45 minutes. All these can make a significant difference.

Reference

Ahmadi MN, Coenen P, Straker L et al (2024). Device-measured Stationary Behaviour And Cardiovascular And Orthostatic Circulatory Disease Incidence.  Int J Epidemiol. 53(60: dyae136. DOI: 10.1093/ije/dyae136

*Note that the study's large population use and the use of devices to measure objective data strengthen the findings. However, observational studies may not totally establish cause and effect. Also since the average age of the subjects was about 61 years, it may not totally apply to younger popuplations.

Single Leg Versus Double Leg Training

L leg bigger

We see many cases where patients have one limb bigger than the other in our clinics. There is an imbalance or deficit between limbs e.g. healthy versus injured, left versus right or dominant versus non dominant. This is also known as interlimb asymmetry in research. 

Strength, power, reactive strength have been shown to be affected when there were interlimb asymetries, especially in sporting performances. I have seen differences of 10-15 percent in deficits for patients even 5 years after they had surgery. Hence, I often suggest that patients work on single limb exercises to reduce this deficit/ asymmetry.

Single leg and double leg strength exercises, plyometrics, balance and even core training have been investigated in a wide variety of athletic populations to understand the effects of interlimb asymmetry. The following systematic analysis was to examine if training interventions are effective in reducing interlimb asymmetries and which types of interventions were more effective in the athletic population.

The single leg counter movement jump (SLCMJ), single leg broad jump (SLBJ), single leg lateral jump (SLLJ) and change of direction (COD) speed were the most commonly used test to check for sprint performance, jump height and COD speed.

Ready for the results? The review suggested that all training interventions have a small to moderate effects on the reduction of asymetry in SLBJ, SLCMJ and COD speed from pre to post training, although no statistically significant differences were reported. This was found in the intervention groups versus the control groups.      

The researchers suggested both unilateral and bilateral training should be considered to decrease interlimb asymmetries. If you're an athlete and have any limb asymmetries and no pain, then definitely do both single and double leg exercises to reduce the asymmetry. 

Please note that the above study was done on athletic populations. I will definitely avoid single leg exercises in the recently injured/ immediate post surgery patients and get them to do bilateral leg exercises first.

What about patients who are not loading equally a year (or longer) after a knee replacement or ACL reconstruction? I always see patients who tend to compensate too much with the non injured/ painful leg. By doing single leg exercises (pictured above), I can make their weaker side work harder.

Reference

Bettariga F,Turner A, Maloney S et al (2021). The Effects Of Training Interventions On Interlimb Asymmetries: A Systematic Review With Meta-Analysis. Strength Cond J. DOI: 10.1519/SSC.0000000000000701

Your Workout Today May Trigger A bright Idea Next Week

Picture from Triana et al (2024)

What if I told you your exercise session today can trigger a bright idea next week? That's exactly what a recent study by Finnish researchers found. They tracked a person's brain and behavioural activity for 5 months using brain scans and data from smart phones and wearable devices. 

This research (Trinan et al, 2024) was unusual since few brain scan studies involve such detailed monitoring over months. Using wearable technology in this study was crucial, especially since brain scans (while being useful) only shows the subject lying still for 30 minutes. 

2 distinct patterns were identified by the researchers. A short term wave that lasted under 7 days and a long term wave by up to 15 days. The short term wave reflects rapid adaptations like how focus is affected by poor sleep although it recovers quickly. The long term wave suggests more gradual, lasting effects, especially in areas tied to our attention and memory.

The study found that our brains do not respond to our activities of daily living in immediate, isolated bursts. Our brain activity evolves in response to our sleep patterns, physical activity, mood, and respiration rate over many days. This means that your exercise session or a restless night from the previous week can still affect your brain. Hence your memory, cognition and attention can be affected well into the next week.

It is a great study linking brain activity with environmental and physiological data as tracking our brain changes in real time can help detect mental health and neurological disorders early. This allows for earlier interventions and better outcomes.

Even though this study was not focused exclusively on exercise, the results showed that we definitely need a consistent exercise routine and maintain good sleep habits for our overall well being. I find myself particularly sensitive to these as I age. 

Reference

Triana AM, Salmi J, Hayward NME et al (2024). Longitudinal Single-subject Neuroimaging Study Reveals Effects Of Daily Environmental, Physiological, And Lifestyle Factors On Functional Brain Connectivity. Plos Bio. DOI: 10.1371/journal.pbio.3002797