Does Concurrent Resistance Training & Endurance Training adaptations Interfere each other?

As you may know that resistance training results in increased muscle fiber size, Whereas endurance training does not increase fiber size instead it increases "Mitochondrial Genesis". So here the question arises, Does one type of training really interfere with the effects of  one another?

Here we say, "Performing Resistance Training & Endurance training results in impaired strength gains when compared to performing resistance training alone".Read below to know about the mechanisms responsible for the impairment of the strength development.

Neural Factors: It is believed that concurrent training impairs motor unit recruitment and therefore decrease the muscle force production.

Decreased Muscle Glycogen: Successive bouts of either strength or endurance training can produce chronically low levels of muscle glycogen. Beginning a training sessions with low muscle glycogen can reduce the ability to perform resistance training sessions and impair the magnitude of strength training adaptations because resistance training relies on anaerobic metabolic pathway.

Decreased Protein Synthesis: Resistance training increases muscle contractile protein synthesis by the activation of mTOR (Mammalian Target of Rapamycin) signalling pathway, whereas Endurance training increases AMPK (Adenosine Monophosphate-activated Protein Kinase) activation and promotes the mitochondrial biogenesis. Then AMPK activates signalling molecule called TSC2 (Tuberous Sclerosis Complex 2) which inhibits mTOR activity eventually it impairs protein synthesis

Hence AMPK/TSC2 pathway explains a biochemical links to why Concurrent Endurance Training & Resistance training may impair strength gains. Below is the diagrammatical representation of AMPK/TSC2 pathway and how it affects the strength gains

Biochemical effects of endurance & Resistance training

 on decreased protein synthesis

(AMPK/TSC2 pathway)

Research Findings #1

Study has conducted in 15 untrained individuals and they have grouped into three Each group has 5 individuals . 

• Group A has done Combination of strength training & Endurance training
• Group B has done Strength training only
• Group C has completed Endurance only training
• Study Duration: 10 weeks of period

Group A have shown similar gains in VO2 max in comparison with Group C but less in strength than Group B

Group B have shown increased strength in the entire ten weeks

Study conclusions: 

• Potentially,  Frequency,Duration and Intensity of training has an impact on the potential for one type of training to interfere with other and that impairs the strength gains directly.
• Mechanisms observed in the study was Neural activation, accumulation of metabolities such as inorganic phosphates , H+ ions and ammonia. Depletion of ATP, CPr and muscle glycogen. These mechanisms underpin this interfere is not well understood
  

•  Power and Endurance

Power is the feature most negatively affected by concurrent training. Studies shows that a relatively short endurance sessions per week are enough to blunt power

Hypertrophy, Strength and Endurance

• Compared to power training, Hypertrophy/Strength is less negatively affected with endurance training (2-3 sessions per week , 20-60 mins per sessions)
• Long and/or frequent endurance session are added to resistance training and it shows that muscle hypertrophy and strength will be compromised.
• Strong blunting effect on 1-RM when running exercises (40 mins of 6 sessions per week) were added to a 10 week resistance training program

HIIT (High Intensity-Interval Training) and Strength/Power

• HIIT might have an impact on strength/power due to its potential peripheral fatiguing effect, where HIIT performed to prior to resistance training will reduce the force generating capacity and resistance volume. The mechanism is not well known but it is believed that alterations in the neuromuscular recruitment patterns
• Therefore reducing training volume rather than intensity seems more important for avoiding the potential interfering effects of concurrent training

In the bottom line,

Now you may know the basic mechanisms which are interfering in the concurrent training. Recall the specificity principle of training before incorporating endurance training with resistance training. Altering the FITT principle in the right way is key to prescribe a clean and right program for your clients. In case of plateau or decreased in performance occurs consider the above mentioned principles and plan the training program accordingly.