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Neuromuscular Adaptation

Anas Maqba

Anas Maqba

Researched by:

Neuromuscular/Neuromuscular Junction/Neuromuscular Adaptation

The SYNAPSE that joins the MOTOR NERVOUS SYSTEM with the SKELETAL MUSCLE FIBERS.
Adult mammalian NMJs are not rigid structures, some degree of remodeling i:e addition or reduction, which also means structures are not stable. They are rapidly changed by external stimuli and decline with age PMID: 15577901 PMID: 9046071 PMID: 22701595 PMID: 21935939 but the rate of remodeling differs depending on the type of muscle.PMID: 2465393 PMID: 1903804

Exercise helps to maintenance and recovery of NMJ.PMID: 12070181 PMID: 18650917 PMID: 21498059 PMID: 11754180

A motor neuron can innervate 1000 muscle cells/fibers.

Strength exercise can increase the number of filaments per myofibril, myofibrils per muscle fiber, and filament area density; thus there is a rise in both muscle cell size and strength. We know little about the influence of strength training on sarcomere length.

The sliding filament theory is a Physico-chemical theory accounting for the MECHANICAL, CHEMICAL, AND STRUCTURAL features of skeletal muscle.

 

Communication between the muscle and motor neuron

Our  opinion: Again, it shows repetition results in NM Adaptation.

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First it built Neuromuscular connection strong as now as adaptation, which is the process of brain learning which builds new neurons(brain cells & their connection with each other) which happens in any form of learning.

LOGIC-Since neuromuscular adaptation includes a learning and coordination process; thus it may take time.

Science-

Logic – To construct a neuromuscular connection, you must first transmit a signal from your action to get feedback from the brain.

Science – Send signal from muscle fibres like BDNF, GDNF, NT-3, and NT-4 to receive signal from nerves like acetylcholine.

Logic- Because the brain must build new connections with muscles to perform movements or improve strength during the learning phase, neuromuscular adaptation should take place first.

Science -Exercise causes NMJ hypertrophy by increasing muscle fibre diameter as well as directly modifying NMJs.

SCIENCE: Rest during the strength protocol (180 s), however, would have allowed muscle blood flow to return to a normal state, limiting exposure to stress. This would have allowed greater time of BDNF removal through uptake in the periphery and possibly the brain.

Whereas Hypertrophy, rep range resulted in greater blood flow which would result in increase blood lactate and short rest period between set would have allowed delay in BDNF removal.

2011 RCT Study Showed Training once per week was sufficient to maintain positive neuromuscular adaptations, though older men (aged 60-75) required higher training volume to maintain their gains compared to younger men (aged 20-35).PMID: 21131862

Because our brain (neurons) remembers everything, even if we lose something from our body, liposuction can kill someone if done severely.

According to the current studies, 10-repetition range training (70% and higher based on 1RM) until failure on compound movements (larger muscle), specific rest durations, and lower-body strength training are required for producing changes in BDNF.

Logic: It is a growth hormone that should have an effect on every system in the body.

Science: Insulin-like growth factor-1 (IGF-1) preserves NMJs in a motor neuron disease mouse.(PMID: 15657392)

Logic: 

Science:electrical stimulation of the sciatic nerve increases NT-4 expression in skeletal muscles. RAT PMID: 7770776

Hence, an injured body part requires brain connection via artificial electrical stimulation; it also indicates that movement of that specific muscle or joint is required to recover.

STUDIES

2010 5 Weeks RCT Study showed (#20 untrained males# 21-22 age #3 training sessions/week #4 sets #6 repetitions #bench press and squat exercises)
Serum BDNF levels increased by 32% but decreased to 41% below resting levels. 
Study Strength: Measured BDNF 1 min, 30 min and 60 min after training. PMID: 20553806

2016 Comparative 9 Week Study Showed (#20 men# 2 years trained #4 times/week#squats, deadlifts, bench press, shoulder press, chin up, leg press, triceps extensions#nutrient intake and diet analysed)
BDNF concentrations were significantly increased in both the high-intensity (3–5 reps; 90% 1RM) and high-volume(10–12 reps; 70% 1RM) groups.
Study Strength:The longest study with positive results after 9 weeks and a total of 40 training sessions with 20 experienced, resistance-trained subjects.
Measured BDNF 60 min post-exercise in addition to immediately post- and 30 min post-exercise levels. PMID: 27231312

2017 Study Showed (#16 subjects#untrained #22-26 age #30 mins exercise #60 s rest #3 sets#bench press, pull down, leg press, leg extension, seated rowing, military press and dumbbell curl).
Compared to strength training(5RM,5 sets 180s rest), the hypertrophy program(10RM,3 sets 60s rest) resulted in a 13% rise in peripheral blood BDNF levels.
Study limitations: Fewer subjects, beginners, acute measurement of BDNF after strength training.PMID: 28511848

2020 RCT Study Showed (# 12 men # 25-30 age #trained #10 rep (Hypertrophy) #Failure #90s of rest #45 leg press, leg extension, and leg curl).

  • When serum BDNF levels were measured at rest, immediately after exercise, 1 hour later, and 2 hours later during recovery. The lower-body group had about twice the impact size of the whole-body group and more than four times that of the upper-body group. However, no significant changes across situations were detected.
  • The amount of work done by bigger muscles has a greater impact on BDNF than total volume.
  • Training intensity beats training volume.
  • Compound Movements beats Isolation Movements.PMID: 33105359

 

2020 2 Week Study Showed (#15 men, 15 female  #bench press and squat, #4 sets# Trained 3 months)

  • Despite differences in Resistance Training Program 5 submaximal repetitions at 70%, 1RM  & 10 submaximal repetitions at 35%, 1RM,a similar acute neurotrophic response was observed when the Total load lifted is equated.
  • The intensity of resistance training is not a significant factor on the neurotrophic factor response when the total load lifted is equated in the range of submaximal repetitions.

Limitation:

  • Blood was drawn 10 min before and 10 min after each training session to analyze serum BDNF levels.
  • Submaximal Repetition means not reaching failure.
  • Both groups had the same rest time of 120 seconds. 120 seconds is too lengthy, particularly for the 10 repetition group.PMID: 33312290

2020 6 Weeks Study Showed (#15 men # ≥2 Trained  # age 23 -25 # 3×/week #back squat & bench press).

No significant interactions or main effects for BDNF. There was a moderate between-group effect size in favor of Low Repetition.

LIMITATIONS:

  • Only well-trained subjects; Therefore, it is possible that in young men who are well-trained, the magnitude of acute BDNF elevation is lower.
  • Min Training volume threshold may be needed to elicit BDNF.
  • A close proximity to failure may be needed to elicit BDNF. PMID: 31790279

2010 Study Showed (#11men #isokinetic training #knee extension). 

Serum BDNF levels increased during exercise but not afterward with isokinetic training including knee extension.

LIMITATIONS:

  • Used Isokinetic Training 
  • Isolation movements not compound.PMID: 21053157 

2010 Study Showed (#16 men #age: 26.4 - 30 #untrained #isokinetic training). 

The results showed no significant results for plasma concentrations of BDNF in either the upper (elbow flexors)  or lower-body  (knee muscles) protocols with isokinetic training.

STRENGTH : Reported the time under tension (TUT) for each set performed. 

LIMITATIONS:

  • Did not report training intensity based on one repetition maximum.
  • The rest periods between performed sets seem very short (40 s), the minimum rest needed was 60 s for a positive BDNF response.
  • No Compound movements nor free-weight training.PMID: 21243284

2010 10-week RCT Study Showed ( #15 untrained #18-30 age #1RM was measured #3×10 reps,80%RM#chest press, shoulder press, vertical traction, leg press, adductor strength, and abductor strength# 3 sessions/week 1RM was reassessed in the 6th, 12th, 20th, and 30th session#BDNF measured min 24 h  before and after  training (30 sessions) also before and immediately after the 6th training session and the 30th session  # ANOVA model #Duncan's multiple range post hoc tests #Pearson's correlation  showed no effect on BDNF).PMID: 20467874

LIMITATIONS:

  • No Nutrition was prescribed to the participants.
  • No mention of failure.
  • 10 repetitions for 80% RM looks less intensity, but may be intense for an untrained one.
  • Participants drop out, 15 out of 30.
  • The weight in the experimental group was higher compared to the control group.
  • BDNF measured in a peripheral vein and not from the brain arteriovenous differences over the brain.PMID: 19923361 PMID: 18629433 PMID: 18484197 Hence, the power of the study is relatively low.

My opinion: Even though the research has limitations, we can see that a high repetition range may not work for BDNF and that a specific stimulus is needed.

2009 12-week study showed ( #27 sports students such as basketball, handball, or football but no experience with strength training#age: 22 – 23 #whole-body training#3x/week#leg extension, leg curls, bench press, pull-down, leg press, seated rows, crunches, hyperextensions, and lateral raises# 8–10 reps 0f 70-80% RM).

There were no significant changes for BDNF.

STRENGTH:Longer intervention and with a large sample size.

LIMITATIONS:

  • No specific rest periods were used.
  • Intensity was 70–80% without any strength test prior, i:e 1RM except knee extension.
  • Only abdominal muscles (Crunches) and lower back (Hyperextension) until Failure.PMID: 18975254

     

2017 crossover study showed (#11 untrained (n=13) & intermediately trained (n=3) males#age: 25.-26 # 5 untrained females age: 23.-24 #5×5 # 180s rest#3×10 #60s recovery #failure # measured BDNF immediately post 30 min post-exercise). 

When compared to strength training, hypertrophy produced noticeably higher levels of BDNF. Following hypertrophy exercise, there was a positive correlation between changes in lactate and BDNF from baseline to post-exercise, but not after strength training.

No differences in mean mechanical work between the strength and hypertrophy program. 

Differences in mean volume load between strength and hypertrophy program were significant but negligible in magnitude. 

Mean tonnage was greater in the strength program when compared to the hypertrophy program.

STRENGTH:

  • Good interset rest durations (60 s).
  • 7 exercises are taken compared to only two (bench press and squat) compared to other studies which influenced the skeletal muscle exposure to peak levels of blood flow.PMID: 28511848

REPETITIONS

  • If the intensity is set too low for performing the required number of repetitions, the results are not entirely valid.
  • It is better to train in the 10 to 15 rep range once a month.
  • It also shows that repetition between 10-12 is required to strengthen the Neuromuscular Junction.
  • Finally, the intensity should correspond to the 1RM wavelength. 

 

MOVEMENT SELECTION

  • Priorities compound Movements.
  • A larger muscle group promotes greater release of BDNF as a result of greater blood flow to the mass of active muscle tissue.

 

FAILURE

  • Sometime reaching failure is important.
  • Increased blood flow is dependent on Intensity.

 

REST PERIOD

  • Studies that used specific (correct) rest periods found a positive BDNF response to a resistance training protocol.
  • Not to take long rest time between sets.
  • It may decrease overall training intensity means reducing blood flow, which will minimize endurance stimulus and reduce in blood lactate(a metabolite associated with changes in peripheral BDNF).
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