Time to Reconsider Muscle Confusion

Most people perform cardiovascular and strength training in the same session because it seems to achieve multiple goals at the same time. Yet scientists and trainers continue to ask whether or not this approach really achieves multiple goals or is, in fact, counterproductive. The answer seems to lie in the fact that our muscles are smart—they know the difference between cardiovascular, strength and flexibility work.

Muscles get confused (just like you and I sometimes do). If you walk into a yoga studio ready to do yoga, but the room is filled with indoor cycles, you get confused. Muscles are the same way. When you combine strength and cardio in the same session, your muscles get confused at the molecular level. The molecular mechanisms associated with gains can cancel each other out, which will diminish your results.

It is widely accepted that combined training adversely impacts strength, but not endurance. Therefore, we will look at ways to program to overcome muscle confusion and achieve strength gains, while not forgetting about cardiovascular and flexibility training. The primary programming factors for you 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; strength and power measurement) were compromised up to two days after high-intensity strength training on alternating days (Doma and Deakin, 2013). The data shows us that full recovery from high-intensity strength training (typically defined as 85% or higher of 1RM max) requires at least 48 hours of rest.


Based on what we saw above on recovery, if you design a program that includes both muscle strength and endurance goals, it is best to schedule each type of exercise on alternate days. Other programming suggestions include limiting endurance-training frequency to fewer than three days per week to minimize the effects on strength (Wilson et al., 2012).

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, for example, that running combined with strength training results in greater strength loss than cycling combined with strength training (Doma and Deakin, 2013). Consequently, it is recommended to include cycling in combined training programs versus running where strength is the primary goal.


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 (Jones et al., 2017; Wilson et al., 2012). 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 your client’s overall fitness goals? The periodic frequency of moderate- to high-intensity sessions might be warranted and should be considered on a case-by-case basis.


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 gains (Jones et al., 2017).

Key Programming Points

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

  • 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.
  • Keep endurance sessions to between 20 and 30 minutes.

Want to learn more from Amy Ashmore? Check out our Programming for Strength Gains: New Research Exposes Timing as the Key Variable online course.


Doma, K. and 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), 34-38.

Jones, T.W. et al. (2017). Effects of strength and endurance exercise order on endocrine responses to concurrent trainingEuropean Journal of Sports Sciences,  17, 3, 326-334.

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.