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The Effect of Concurrent Training
Len Kravitz, Ph.D.

Countless numbers of recreational workout enthusiasts complete their cardiovascular and resistance training workouts during the same training session, or within hours of one another. This sequential exercise regime is referred to as ‘concurrent training’. For many clients, the question and concern often posed to the personal trainer is whether the aerobic exercise will impair the resistance training workout performance. This recent publication, by Sporer and Wenger (2003), addresses this question as well as some related meaningful training issues.

Background and Theoretical Basics With Concurrent Training
The research on concurrent training, where aerobic exercise precedes resistance training, is inconclusive how strength improvements are affected. Several investigations have shown strength improvements are impaired while other studies show no impairments in strength training. Much of the inconsistencies in research on concurrent training reflect differences on one or all of the following:
1. Type of strength training method (i.e., isokinetic and isotonic)
2. Intensity and/or duration of the aerobic exercise
3. The intensity (% of repetition maximum) and/or volume (reps x sets) of the resistance exercise performed
Since little ‘basic’ research (research performed to determine the underlying mechanism of a phenomenon) has been completed on current training, the theoretical basis how strength training is affected by preceding aerobic exercise is mostly speculative. One prevalent concept explaining how aerobic exercise affects strength outcomes is the ‘fatigue’ hypothesis, which states that the strength training performance is reduced due to fatigue from the aerobic exercise. Muscle fatigue is a multi-factorial phenomenon caused by cellular protons (H+) increasing acidosis, decreases in energy-providing substrates, decreases in neural drive, and muscle cell damage (Sporer and Wenger, 2003). More research is needed in this particular area to attempt to identify a specific mechanism(s) how previous aerobic exercise may (or may not) impair strength performance.

Study Methodology
This very sophisticated study actually investigated 3 research questions.
1. Does prior aerobic exercise compromise strength training, and if so, for how long?
2. Does the intensity of aerobic training have a varying affect on strength performance?
3. Is acute strength training affected depending on muscle groups used in aerobic exercise?
Seventeen male athletes (3 hockey players, 2 rugby players, 1 rower, 3 tennis players, 1 soccer player and 7 recreational athletes) who were strength training (2-3 times per week) for the previous 6 months were recruited for the study. Sixteen subjects completed the study.

It is noted that subjects were initially divided into a high intensity aerobic group or a submaximal aerobic group on cycle ergometers. The high-intensity aerobic group performed a 5-minute warm-up, six 3-minute exercise intervals from 85 – 100% of maximum cycling power output of their VO2 max, separated by 3-minute recovery periods (performed at 40% of maximum cycling power output of their VO2 max), finishing with a 5-minute cool-down. The submaximal aerobic group performed a 5-minute warm-up, 36 continuous minutes at approximately at 70% of maximum cycling power output of their VO2 max, finishing with a 5-minute cool-down. Each of these groups then performed a resistance training session (each trial separated by 72 hours) under the following conditions:
1. Control – Strength training with no previous aerobic exercise
2. 4-hour recovery – Strength training four hours after aerobic exercise
3. 8-hour recovery - Strength training eight hours after aerobic exercise
4. 24-hour recovery - Strength training 24 hours after aerobic exercise
To mimic a typical resistance training session, all subjects performed 4 sets of incline leg press and 4 sets of bench press at 75% of their one repetition maximum. For each set, subjects performed as many repetitions as they could successfully execute. This is how the four conditions were statistically analyzed
No significant different was found between the different intensities of aerobic exercise on the subsequent resistance exercise training session. The researchers therefore combined the high-intensity aerobic group and the submaximal aerobic group data to compare the results (of both groups) on the different recovery periods. The recovery time comparisons of the incline leg press are presented in Table 1 with the bench press results in Table 2.

Table 1. Incline Leg Press Results of All Subjects (n=16)
Control 4-Hour 8-Hour 24-Hour
All Subjects Combined (reps) 48 36 44 49

Table 2. Bench Press Results of All Subjects (n=16)
Control 4-Hour 8-Hour 24-Hour
All Subjects Combined (reps) 32 32 32 32

For the leg press, at both the 4-hour and 8-hour recovery conditions, the repetitions were significantly lower than the control (no aerobics performed) and the 24-hour recovery group. There was no difference between the control group and the 24-hours group.
There was no difference in bench press repetitions performed between any of the conditions. As shown in Table 2, the average repetitions performed on each condition was 32 repetitions.

Major Practical Findings of the Study
The three major practical findings of this study are:
1. The effect of recovery on strength performance following aerobic exercise (on a cycle ergometer) is similar regardless of the intensity of aerobic exercise. There was no difference in strength training performance when subjects performed high-intensity interval training (high-intensity intervals above 85% of maximum aerobic capacity) or submaximal continuous training (at 70% of maximum aerobic capacity).
2. Strength impairments are limited to the muscle groups used in the prior aerobic training. Cycle ergometry is a lower body cardiovascular modality. Bench press output was not impaired regardless of the condition (no prior aerobics, 4-hour recovery, 8-hour recovery, and 24-hours recovery). Thus, clearly there is no impairment of resistance training work when the prior aerobic exercise utilizes different muscle groups (for the mode of exercise).
3. Incline leg-press was dramatically influenced by the aerobic exercise. It is clear from the results in Table 1 that all of the trained subjects were not capable of completing an equivalent number of repetitions (at the same percentage of their one repetition maximum) for all conditions. Further inspection of Table 1 shows that strength output was most noticeably weakened during the 4-hour recovery period, with the next highly affected condition being the 8-hour recovery period.

Practical Application for Personal Trainers
This well-designed study reveals constructive insights for personal trainers who train some clients with cardiovascular and resistance exercise within the same session. When the sequence involves aerobic exercise followed by resistance training, the personal trainer may be well advised (from results of this study) to attempt to emphasize different muscle groups during the aerobic training as those conditioned in the resistance exercise. There was no significance difference in the intensity of aerobic exercise completed prior to the subsequent resistance workout; so this decision can be made exclusively on the cardiovascular goals of the client for that workout. Should the trainer wish to ensure no compromise of strength training output in a concurrent workout session, another educated option is to perform the resistance exercise first, followed by the aerobic training. One research question, not addressed by this study that needs to be addressed by future studies is whether LONG-TERM strength outcomes are truly affected by aerobic exercise performed prior to resistance training.
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