Chris Beardsley is a co-founder of Strength and Conditioning Research, a monthly publication that summarizes the latest fitness research for strength and sports coaches, personal trainers, and athletes. The views expressed herein are his.

The fitness industry can be a confusing place, with many experts providing conflicting opinions. Scientific research is our best shot at providing objective and effective approaches to fitness. Strength and Conditioning Research is a monthly review service that covers new and interesting scientific studies on fitness topics. The studies included help answer difficult questions about optimal fitness, training, and body transformation.

Here are the summarized results of three recent studies that were covered in the review along with what those results mean for us.

Combining Strength and Endurance Training Could Increase Muscle Gains

Photo by Justin Singh

Recently, researchers led by Jussi Mikkola at the Research Institute for Olympic Sports in Finland found concurrent strength and endurance training is counterproductive for improving explosive strength, while it could actually be better than strength-only training for improving muscle sizeNeuromuscular and cardiovascular adaptations during concurrent strength and endurance training in untrained men. Mikkola, J., Rusko, H., Izquierdo, M., et al. Research Institute for Olympic Sports, Physiology, Jyväskylä, Finland. International Journal of Sports Medicine. 2012 Sep;33(9):702-10..

What did the researchers do?

The researchers recruited 44 healthy but untrained adult males for a 21-week study. The subjects were assigned to either resistance training only, endurance training only, or concurrent training groups.

The resistance training was performed twice a week and comprised two leg exercises: the leg press and the knee extension machine. The endurance training carried out twice a week and increased in both duration and intensity from 30-minutes sessions through to 60 – 90-minutes sessions over the 21 weeks.

Before and after the 21-week training program, the researchers measured the knee extension strength and rate of force development of the subjects, as well as the cross-sectional area of their thigh muscle.

What happened?

The researchers found that only the strength-only group improved rate of force development significantly, by 38 ± 31 percent while the strength-endurance group actually decreased rate of force development by 7 ± 51 percent.

Rate of force development is very important for power athletes, as it determines how quickly the athlete is able to reach their full strength capability. In explosive sports, rate of force development is often more important than maximum strength.

However, the researchers found the cross-sectional area (size) of the thigh muscles increased by more in the strength-endurance group (11 ± 5 percent) than in the strength-only group (6 ± 5 percent).

What did the researchers conclude?

The researchers concluded that concurrent strength and endurance training optimizes gains in muscular size but interferes with improvements in explosive strength, as measured by rate of force development.

What does it mean for you?

If you are doing resistance training purely for power, perhaps because you compete in a Track and Field sport, then endurance training may reduce the gains you make from resistance training. On the other hand, if you are carrying out resistance training for your physique, some endurance training could actually enhance your results.

Eccentric Training Increases Muscle Length and Flexibility

In a recent review study led by Kieran O’Sullivan from the University of Limerick in Ireland, the reviewers found eccentric resistance training actually increases leg muscle flexibility, regardless of the muscle group studiedThe effects of eccentric training on lower limb flexibility: a systematic review. O’Sullivan, K., McAuliffe, S., Deburca, N. Department of Clinical Therapies, University of Limerick, Limerick, Ireland. British Journal of Sports Medicine. 2012 Sep;46(12):838-45. Epub 2012 Apr 20..

In normal strength training, an exercise is divided into two phases: the eccentric (lowering) phase and the concentric (lifting) phase. Eccentric training in research is where only the lowering phase is used. In practice, most lifters simply emphasize the lowering phase in order to obtain many of the same results.

What did the reviewers do?

The reviewers looked at a wide range of databases, concentrating on those that provide the highest quality of evidence: randomized clinical trials (RCTs). They included studies in their review that investigated the flexibility effects of eccentric training over a training period of longer than 4 weeks.

Their initial search revealed 285 individual studies, but after elimination of studies that did not fit all of the relevant criteria, the researchers were left with just six. However, the methodological quality of these six studies was rated as being very high, which means that we can be fairly sure that they are reliable.

What did the reviewers find?

The reviewers found all six studies showed clearly that eccentric training improved lower body flexibility, irrespective of whether the muscle group tested was the calves, the hamstrings, or the quadriceps.

What does it mean for you?

If you use lower body stretching in your routine and feel that you don’t have time for resistance training, you could try eccentric leg muscle training, which would kill two birds with one stone.

You could do this by performing movements that stress longer muscle length and emphasizing the eccentric component. Good choices would be: Romanian deadlifts for the hamstrings, single leg elevated calf-raises for the gastrocnemius, and Olympic-style squats to full depth for the quadriceps and gluteals.

Periodization Could Make a Big Difference in Strength Training

Recently, researchers from Brazil led by de Lima found the type of periodization used during a muscular endurance-training program altered how effective the training was at improving muscular endurance and reducing body fatLinear and daily undulating resistance training periodizations have differential beneficial effects in young sedentary women. de Lima, C., Boullosa, D.A., Frollini, A.B., et al. Health Sciences Faculty, Methodist University of Piracicaba, Brazil. International Journal of Sports Medicine. 2012 Sep;33(9):723-7. Epub 2012 May 4..

Periodized training involves a general plan for sets and reps for a given number of weeks or months of training. Linear periodization involves starting with a number of workouts of higher rep training and gradually decreasing the number of reps and increasing the weight over a period of several weeks or even months.

What did the researchers do?

The researchers recruited 28 young women and allocated them into three groups: linear periodization, daily undulating periodization, and a control. In both training programs, the subjects performed four workouts per week of which two were the same, in an A-B-A-B format. However, one program followed a linear progression and the other followed a daily undulating progression.

In the linear periodization program, the subjects performed 3 sets of 30RM in the first week, 3 sets of 25RM in the second week, 3 sets of 20RM in the third week, and 3 sets of 15RM in the fourth week. This pattern was repeated two further times in the 12-week training period.

In the daily undulating program, the intensity and volume were modified in the same week. In weeks 1, 3, 5, 7, 9, and 11, the subjects trained on days 1 and 2 with 3 sets of 30RM and on days 3 and 4 with 3 sets of 25RM. In weeks 2, 4, 6, 8, 10, and 12, participants trained on days 1 and 2 with 3 sets of 20RM and on days 3 and 4 with 3 sets of 15RM.

What happened?

The researchers found that both programs produced a significant decrease in body fat percentage and fat mass.

They also found the linear periodization program produced a greater reduction in body fat percentage than the daily undulating program. On the other hand, the daily undulating periodization model produced a significantly higher muscular endurance increase than the linear periodization model.

What did the researchers conclude?

The researchers concluded that, in a muscular endurance resistance-training program, linear periodization was superior for improving body composition while daily undulating performance was more effective for improving muscular endurance performance.

What does it mean for you?

If you make use of muscular endurance training and your goal is to lose body fat, then a linear periodization is more effective than a daily undulating program. However, if you want to improve muscular endurance, then a daily undulating periodization would be a better choice.

Will these findings impact your approach to fitness? Share in the comments below and talk with the author on Facebook!