Hitting it After Weights - Nothing but Benefits? Not Exactly, but Systemically Impaired Strength & Size Gains are a Myth

Has your cardio-addiction held you back in the past? That does not mean that a short HIIT training after an RT workout will do the same, does it?

Right from the University of Athens comes new paper by Tsitkanou et al. (2016). In their study the Greek scientists investigated whether high-intensity interval cycling performed immediately after resistance training would inhibit muscle hypertrophy and strength improvements induced by resistance training per se.

Based upon previous studies utilizing low-intensity cycling as well as acute studies investigating molecular pathways it was hypothesized that high-intensity interval cycling performed immediately after resistance training would not hinder muscle strength and hypertrophy but would negatively affect the rate of force development. So, no effect on muscle but on strength gains.
The subjects, twenty-two male university students (age 21.8 0.6 years, body height 177.4 1.5 cm, body mass 74.2 2.1 kg, estimated VO2peak on a cycle ergometer 38.2 0.9 ml/kg/min) who had not been involved in systematic training (resistance or endurance) for at least 6 months before the initiation of the study but participated in recreational activities such as basketball, soccer, and jogging, 2–3 h per week, were assigned into two experimental groups according to their initial 1-RM leg press strength:

"One group of participants (RE, n = 11) performed resistance training only and the other group (REC, n = 11) performed the same resistance training but each session was followed by high-intensity interval cycling. [...] Training was performed two times per week for 8 weeks. Warm-up was the same for both training groups and included 5-min cycling at 50–75 W, lower body muscle stretching and 2 sets 9 - 10 repetitions of three exercises for the trunk (abdominal crunches, lateral crunches, dorsal raises) aiming to strengthen the lumbar spine area for injury prevention. The inclined leg press (45° angle) and the half-squat (knee angle 90°) Smith machine were used for the strength training of the lower extremities. The RE group performed four sets of 6-RM for each exercise (Zaras et al., 2014; approximately 85% of 1-RM: 220 14 kg and 127 +/- 7 kg in leg press and in halfsquat, respectively). In the first week, the training load was set at 80% of 6-RM (176 +/- 11 kg and 102 +/- 6 kg in leg press and half-squat, respectively). Thereafter, the resistance training load was set at 6-RM and it was increased by 2.0–2.5% in every training session so as to maintain at 6-RM until the last week of training intervention" (Tsitkanou. 2016).

Unlike the previously described resistance training protocol with rest periods of 3 minutes and between sets and 5 minutes between exercises, HIIT cycling was performed only by the subjects in the REC group. 10 minutes after the completion of the resistance exercises, the participants performed 10 sets of 60-s duration on a stationary bicycle with 100% of maximal aerobic power and 55–60 revolutions/min. The cycling workload was being increased (~2%) in every training session. The passive recovery between sets was static and amounted to 60 s.

Figure 1:  Δ Physical performance (%) before and after the training period; *: p < 0.05, §: p < 0.001 (Tsitkanou. 2016).

The authors of the study estimate the extra energy cost of performing high-intensity cycling in REC was less than 50 Kcal per day, for the whole training period. "Therefore, the participants of the REC group did not receive any extra nutritional direction in order to compensate for this extra energy loss
compared to RE," the authors argue and are probably right: it is very unlikely that those 50kcal would have a sign. effect on the lean mass and/or strength gains.

What the data in Figure 1 does tell you, however, is that there was a non-significant effect of the training type; albeit with a practically hardly relevant "advantage" for either of the workout protocols. If anything you may argue that the increase in maximal aerobic power of the subjects in the REC group, though it's likewise not statistically significant compared to the RE group, provides evidence of potentially relevant training benefits that would be confirmed by the significant improvements in heart rate at four submaximal workloads you can see in Figure 2.

Figure 2: Heart Rate at four submaximal workloads before and after 8 weeks of resistance training only (RE, a), and resistance plus aerobic training (REC, b). *P < 0.05, difference before and after 8-week training period (Tsitkanou. 2016).

For resistance trainees that may not be the most important benefit, but in view of the fact that the main muscle size increase, i.e. in the quads, did not differ and considering the fact that the vastus lateralis (VL) and rectus femoris (RF) size gains virtually cancel each other out, a significant systemic impairment of muscle hypertrophy as it is often cited as potential side effect of concomitant training.

Figure 3: Cross-sectional area of the right quadriceps and its’ four heads, and architectural characteristics of vastus lateralis before and after 8 weeks of resistance training per se and resistance plus high-intensity aerobic cycling | †P < 0.05 difference in percentage changes between two groups (RE > REC). ‡P < 0.05 difference in percentage changes between two groups (RE < REC). VL = vastus lateralis; RF = rectus femoris; VI = vastus intermedius; VM = vastus medialis; CSA = cross-sectional area; Quad = whole quadriceps (Tsitkanou. 2016).

Rather than that, the data in Figure 3 suggests an activity-dependent selective hypertrophy of the rectus femoris; whether the vastus lateralis simply gets too much exercise (previous studies show a steep inline in VL activity as the intensity of cycling increases / in running, the EMG activity is many times lower | Bijker. 2002) or if there's another reason for the lack of CSA increases, will have to be investigated in future studies
Since the type of training didn't affect the fiber composition of the subjects, either (both groups seeing similar increases in Type IIA and IIX - without sign. inter-group differences), the study at does indeed confirmed the authors' research hypothesis: "[H]igh-intensity interval cycling performed immediately after lower body resistance training did not inhibit muscle hypertrophy induced by chronic resistance training, in moderately trained individuals" (Tsitkanou. 2016). In fact, the additional increase in muscle capillarization and previously discussed beneficial effects on conditioning would even argue in favor of doing HIIT after every workout if...
References:

• Bijker, K., G. De Groot, and A. Hollander. "Differences in leg muscle activity during running and cycling in humans." European journal of applied physiology 87.6 (2002): 556-561.
• Häkkinen, K., et al. "Neuromuscular adaptations during concurrent strength and endurance training versus strength training." European journal of applied physiology 89.1 (2003): 42-52.
• Kazior, Zuzanna, et al. "Endurance Exercise Enhances the Effect of Strength Training on Muscle Fiber Size and Protein Expression of Akt and mTOR." PloS one 11.2 (2016): e0149082.
• Murach, Kevin A., and James R. Bagley. "Skeletal Muscle Hypertrophy with Concurrent Exercise Training: Contrary Evidence for an Interference Effect." Sports Medicine (2016): 1-11.
• Tsitkanou, S., et al. "Effects of high‐intensity interval cycling performed after resistance training on muscle strength and hypertrophy." Scandinavian Journal of Medicine & Science in Sports (2016).