Why Muscle Confusion is BAD. AVOID Concurrent Training Effect (CTE).

Avoid muscle confusion. Avoid CTE. Make strength and power gains.

Most people do combined training which is simply doing cardiovascular and strength training in the same session. The reason we do it is to save time and get the most out of each workout. Because it seems to achieve multiple goals at the same time it seems like a good thing. But the reality is that it is not, and I’ll tell you exactly why here?

The reason that combined training, also known as concurrent training, is bad IF your primary goals are to gain muscle mass, strength, and power lies in the fact that muscles are smart. They know the difference between cardiovascular and strength work. It is called the concurrent training effect (CTE).

Muscles get confused just like you do. If you walk into a yoga studio ready to do yoga and spin cycles are on the floor you get confused. You ask yourself, “did I have the time right?” Muscles are the same way. When you do combined fitness like strength and cardio in the same session your muscles get confused at the molecular level. The molecular mechanisms associated with each type of training, cardio, and strength, can cancel each other out and results are diminished!

It is widely accepted that muscle strength is adversely impacted by combined training versus muscle endurance. Therefore, we will look at ways to program to overcome muscle confusion and achieve strength gains while not forgetting about cardiovascular training. To protect strength gains, the primary programming factors to consider are length of recovery time after strength training, and the frequency, type, intensity, and volume of endurance training.

Recovery Time

Muscles need 48 hours for baseline strength to recover from high-intensity strength training. This finding is based on data collected from knee extensor torque (KET) which showed that KET and muscle force generation capacity (MFGC; a measure of strength and power) were compromised up to two days after high-intensity strength training on alternating days¹. The data shows us that if we do high intensity strength training (typically defined as 85% or higher of 1RM max) the full recovery requires at least 48 hours.

Frequency

Based on recovery length, if your goals include both muscle strength and endurance, it is best to schedule each type of exercise on alternate days². Other programming suggestions include limiting endurance training frequency to less than three days per week to minimize the effects on strength³.

Type of Cardiovascular Exercise

Frequency and recovery aside, the type of cardio exercise you choose is critical, along with the intensity and volume of it. Independent research shows that running combined with strength training results in greater strength loss than cycling combined with strength training⁴. Consequently, it is recommended to include cycling in combined training programs versus running where strength is the primary goal. Whereas as the most recent data suggests that high intensity interval training, regardless of mode of cardiovascular exercise, is impacts strength gains the least.

Intensity

Another important research finding that will influence your programming is that the extent of strength impairment is directly related to the intensity of the endurance training^{5, 6}. Specifically, moderate to high-intensity endurance training reduced the effectiveness of strength training. Therefore, the intensity of endurance sessions should be decreased to limit the negative impact on strength gains. However, practical considerations and training goals will influence the utility of low-intensity endurance training sessions. In other words, low-intensity endurance training sessions may not negatively impact strength gains, but are they useful to reaching fitness goals? The periodic frequency of moderate to high-intensity sessions might be warranted and should be considered on a case-by-case basis along with the inclusion of high intensity intervals.

Volume

Finally, it is recommended that endurance training sessions last between 20 and 30 minutes to minimize the negative effects of volume or amount of endurance training on strength gains⁶.

Programming Bullets

A summary of suggested programming guidelines is provided below. Note that these apply to a combined training program where the primary goal is muscle strength and power.

• Rest for at least 48 hours after high-intensity exercise (greater than 85% maximum capacity).
• Schedule endurance and strength training on alternating
• Limit endurance training to three or fewer times per week.
• Use cycling versus running as the cardio type.
• Use low-intensity endurance sessions.
• Consider high intensity intervals.
• Keep endurance sessions to between 20 and 30 minutes.

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References

1. Doma, K., & Deakin, G. 2013. The Cumulative Effects of Strength and Endurance Training Sessions on Muscle Force Generation Capacity Over Four Days. Journal of Australian Strength and Conditioning, 21(Supplement 1), 34-8.
2. Wilson, J.M., et al. 2012. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307.
3. Wilson, J.M., et al. 2012. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307.
4. Doma, K., & Deakin, G. 2013. The Cumulative Effects of Strength and Endurance Training Sessions on Muscle Force Generation Capacity Over Four Days. Journal of Australian Strength and Conditioning, 21(Supplement 1), 34-8.
5. Wilson, J.M., et al. 2012. Concurrent training: a meta-analysis examining interference of aerobic and resistance exercises. Journal of Strength and Conditioning Research, 26(8), 2293-2307.
6. Jones TW, Howatson G, Russell M, & French DN. 2017. Effects of strength and endurance exercise order on endocrine responses to concurrent training. European Journal of Sports Sciences. 17(3): 326-334.

Author Biography

Amy Ashmore, Ph.D. holds a doctorate in Kinesiology from the University of Texas at Austin. She is a physical therapy continuing education provider located in Las Vegas, NV.