Strength Training Makes You Stiff And Inflexible ?

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Looking at a bodybuilder, due to the sheer size, and the way they generally move, a common assumption appeared long back, that building larger muscles will make you muscle-bound; or weight training makes you stiff & inflexible.

Well not only has this myth been cleared multiple times in tons of studies, but it is actually shown that resistance training helps improve flexibility, even by itself. Research showed that, resistance training actually helped improve strength around all joints, which is not seen with flexibility training alone.

Remember, that most injuries happen due to lack of strength around a joint, not due to lack of flexibility. When you do static stretching, you are just increasing the pain & stretch tolerance of a muscle, before it reaches a specific length. So, nothing changes in a muscle, in terms of structure.

When, on the other hand, you do a full ROM resistance training workout, actually increases the stretch potential of a muscle, by changing the structure of the muscle. So, you are lengthening & strengthening the muscle at the same time. Even if we talk about purely flexibility, studies have shown that strength training increases flexibility at par with flexibility training, or static stretching.

There are a number of studies to support this fact and bust the age-old myth. Let’s have a look at them:

  1. A 2002 study, showed the effects of a 10-week resistance training program on flexibility of elderly women between 62 and 78 years of age. The control group was composed of 8 women (62 to 73 years old) who were physically inactive. Flexibility was evaluated through the sit-and-reach test, performed both before and after the training program. After an initial evaluation, individuals started a training program, which consisted of 8 exercises for the entire body, without the performance of any flexibility exercise.

The training program resulted in significant increase of flexibility in elderly women (approximately equal 13%). No significant differences were found in the control group. Researchers concluded that weight training without performance stretching exercises does increase flexibility in elderly women.

2. A 2002 study, investigated the effects of aerobic training, strength training and their combination on joint range of motion of inactive older individuals. Thirty-two inactive older men (65-78yr) were assigned to one of four groups: control, strength training, cardiovascular training, and combination of strength and aerobic training. Strength training included 10 resistance exercises for the major muscle groups at an intensity of 55-80% of 1RM and cardiovascular training included walking/ jogging at 50-80% of maximal heart rate. Hip flexion, extension, abduction, and adduction, shoulder extension, flexion, and adduction, knee flexion, elbow flexion and sit-and-reach score were determined before and at 8 and 16 weeks of training.

Researchers found that, strength training and combination of strength and aerobic training, increased strength at the end of the training period. Strength training & combination of strength and aerobic training, increased significantly sit-and-reach performance, elbow flexion, knee flexion, shoulder flexion and extension and hip flexion and extension both at mid- and post-training.

Thus, the results indicate that resistance training may be able to increase range of motion of a number of joints of inactive older individuals possibly due to an improvement in muscle strength.

3. A 2004 study, analysed the flexibility behaviour after 10 weeks of a resistance training program in untrained young adults. 16 inactive men were divided into training group and control group. The training group was submitted to 10 consecutive weeks of RT (three weekly sessions in alternated days), whereas for control group, no program of physical activities was developed in this period.

In the study, significant increase on flexibility between pre-and post-experiment were found in training group. The results of the present study suggest that the 10 first weeks of resistance training practice may contribute effectively for the maintenance or improvement of the flexibility levels observed in the pre-training period.

4. Another 2004 study, determined whether 8 weeks of combined training improves flexibility in older adults with and without type 2 diabetes. Nine individuals with type 2 diabetes (5 men and 4 women) and 10 sedentary control subjects (6 men and 4 women) participated.

Subjects performed flexibility and resistance training on 3 non-consecutive days of the week over an 8-week period. During each training session, they performed three sets of 8–12 repetitions of each of the eight exercises for which their 1RM had been determined, done at 50, 60, and 70% of their individual 1RM. After each exercise session, subjects performed various standard flexibility exercises that stretched the major muscles groups of the chest, shoulders, and legs for 10 –30s each.

Researchers found that, only the type 2 diabetic group, significantly improved on any flexibility measure with training, specifically the modified sit-and-reach, left knee flexion, and left hip flexion measures; no measure for control subjects improved significantly. Additionally, the type 2 diabetic group increased overall lower body flexibility (including right and left knee flexion and hip flexion/extension) significantly more than control subjects.

In conclusion, older adults with type 2 diabetes without impaired flexibility may still enhance certain measures of joint ROM by participating in combined strength and resistance training.

5. A 2005 study, determined the separate and combined effects of resistance training and flexibility training on muscle performance and joint range of motion, and tested the hypothesis that, that increases in muscle strength and flexibility are developed by specific training programs. For the study, 43 young adults were tested before and after 4 different interventions conducted twice a week for 12 weeks: (a) resistance training only; (b) flexibility training only; (c) resistance and flexibility training; and (d) no intervention.

Researchers found that, there was no change in either strength or flexibility in the control group. Resistance training improved muscle strength either alone or in combination with flexibility training, but did not change flexibility. Flexibility increased with specific training alone or in combination with resistance training.

In conclusion, in young, healthy subjects, resistance training alone did not increase flexibility, but resistance training did not interfere with the increase in joint range of motion during flexibility training. These results support the concept that specific training should be employed in order to increase either muscle strength or flexibility.

6. A 2006 study, determined whether resistance exercise intensity affects flexibility and strength performance in the elderly following a 6-month resistance training and detraining period. Fifty-eight healthy, inactive older men (65- 78yrs) were assigned to 1 of 4 groups: a control group, a low-intensity resistance training group (40% 1RM), a moderate-intensity resistance training group (60% 1RM), or a high-intensity resistance training group (80% 1RM). Subjects in exercise groups followed a 3 days/week, whole-body (10 exercises, 3 sets per exercise) protocol for 24 weeks. Training was immediately followed by a 24-week detraining period. Strength (bench and leg press 1RM) and range of motion in trunk, elbow, knee, shoulder, and hip joints were measured at baseline and during training and detraining. 

Resistance training increased upper- and lower-body strength in an intensity-dependent manner. Flexibility demonstrated an intensity-dependent enhancement. Detraining caused significant losses in strength and flexibility in an intensity-dependent manner.

Results indicate that resistance training by itself improves flexibility in the aged. However, intensities greater than 60% of 1RM are more effective in producing flexibility gains, and strength improvement with resistance training is also intensity-dependent. Detraining seems to reverse training strength and flexibility gains in the elderly in an intensity-dependent manner.

7. A 2008 study, investigated the effect of 10 weeks of strength training on the flexibility of sedentary middle-aged women. For the study twenty women were assigned to either a strength training group or a control group. The strength training program was a total body session performed in a circuit fashion and consisted of 7 exercises performed for 3 circuits of 8 to 12RM. Flexibility measurements were taken for 10 articulation movements pre-and post-training: shoulder flexion and extension, shoulder horizontal adduction and abduction, elbow flexion, hip flexion and extension, knee flexion, and trunk flexion and extension

Pre-and post-training, 10RM strength significantly increased. Of the movements examined, only shoulder horizontal adduction, hip flexion and extension, and trunk flexion and extension demonstrated significant increases. Neither elbow nor knee flexion showed a significant change with weight training. The control group showed no significant change in any of the flexibility measures determined. In conclusion, weight training can increase flexibility in previously sedentary middle-aged women in some, but not all joint movements.

8. A 2010 study, investigated the effect of weight training on sprinting performance, flexibility and strength of the 20 students. A 45min weight training schedule twice a week for 12 weeks was administered. The test considered were strength (1RM for all the weight training components), 50m run and sit and reach. 

The analysis of the data reveals a significant improvement in sprinting performance. Flexibility improved from pre-to post-test. All weight training exercises performed like bench press, squat, barbell front press, lat pull down & barbell curls, improved pre-to post-test.

9. A 2010 study, determined whether functional training has similar effects as traditional resistance training on muscular strength and endurance, flexibility, agility, balance, and anthropometric measures in young adults. 38 healthy volunteers, were placed into a control group and an experimental group. The participants were tested prior to and after completing the 7-week training study. The testing battery included: weight, girth measurements, flexibility, agility, lower back flexion and extension endurance, push-up test, sit-up test, one-leg balance, one-repetition maximum (1RM) bench press and squat.

Results indicated significant increases in push-ups, back extension endurance, 1RM bench press, 1RM squat, and one-leg balance within each group following training. Traditional training also elicited significant increases in bicep girth, forearm girth, calf girth, and sit-ups, while the functional training group experienced significant increases in shoulder girth and flexibility.

Collectively, these results suggest that both programs are equally beneficial for increasing endurance, balance, and traditional measures of strength. However, changes in various girth measures, torso flexor endurance and flexibility appear to be program-specific.

10. A 2010 study, examined whether moderately intense resistance training improves flexibility in an exclusively young, sedentary women population. Twenty-four, young, sedentary women were divided into 3 groups as follows: agonist/antagonist (AA) training group, alternated strength training (AST) group, or a control group (CG).

Training occurred every other day for 8 weeks for a total of 24 sessions. Training groups performed 3 sets of 10 to 12 repetitions per set except for abdominal training where 3 sets of 15 to 20 reps were performed. Strength (1 repetition maximum bench press) and flexibility were assessed before and after the training period. Flexibility was assessed on 6 articular movements: shoulder flexion and extension, horizontal shoulder adduction and abduction, and trunk flexion and extension.

Both groups increased strength and flexibility significantly from baseline and significantly when compared with the CG. The AST group increased strength and flexibility significantly more than the AA group. This study shows that resistance training can improve flexibility in young sedentary women in 8 weeks.

11. A 2011 study, determined how full- range resistance training affected flexibility and strength compared to static stretching of the same muscle–joint complexes in untrained adults. After pretesting hamstring extension, hip flexion and extension, shoulder extension flexibility, and peak torque of quadriceps and hamstring muscles, subjects completed 5-week static stretching or resistance training treatments in which the aim was to stretch or to strength train the same muscle–joint complexes over similar movements and ranges.

Post-tests, it was seen that, there was no difference in hamstring flexibility, hip flexion, and hip extension improvement between resistance training and static stretching groups, but both were superior to control group. The results of this study suggest that carefully constructed full-range resistance training regimens can improve flexibility and the typical static stretching regimens employed in conditioning programs. These results question the notion that resistance training will reduce flexibility (the ‘‘muscle bound’’ notion), and they also suggest that the commonplace ‘‘stretch what you strengthen’’ lore is questionable.

12. Another 2011 study, examined the strength and flexibility gains after isolated or simultaneous strength and flexibility training after 16 weeks. Eighty sedentary women were assigned to 1 of 4 groups: strength training, flexibility training, combination of both, and control group. All the groups performed pre-and post-training sit and reach test to verify the flexibility level and 10RM test for leg press and bench press exercises.

The training protocol for all groups, except for the control group, included 3 weekly sessions, in alternated days, totalling 48 sessions. Strength training was composed of 8 exercises for upper and lower body, executed in 3 sets of periodized training. The flexibility training was composed of static stretching exercises that involved upper and lower body.

Results showed that strength training, combination of strength & flexibility training, and flexibility training significantly increased flexibility in relation to baseline and to control group. Strength tests demonstrated that strength training, & combination of strength & flexibility training significantly increased 10RM when compared to baseline, flexibility, and the control group.

In conclusion, short-term strength training increases flexibility and strength in sedentary adult women. Strength training may contribute to the development and maintenance of flexibility even without the inclusion of additional stretching, but strength and flexibility can be prescribed together to get optimal improvements in flexibility.

13. A 2011 study, investigated the effects of 10 weeks of strength training with different number of sets, and its influence on flexibility. Sixty men were divided into three groups: group that trained 1 set per exercise, group that trained 3 sets per exercise and control group). The training lasted 10 weeks, totalling 30 training sessions. The training groups performed 8 to 12 repetitions per set for each exercise. The flexibility at Sit and Reach Test was evaluated pre-and post-training.

Both trained groups showed significant increase in flexibility when compared to pre-training and the 3-set per exercise group showed significant difference when compared to control group post-training. This means that, the strength training performed without the flexibility training promotes flexibility gains regardless of the number of sets.

14. A 2011 study, compared SuperSlow resistance training (SRT) to traditional resistance training (TRT) during early phase adaptations in strength, aerobic capacity, and flexibility in college-aged women. Subjects were randomly assigned to SRT, TRT, or control groups. To equalize training times, TRT trained 3 times per week for 25 minutes each session, whereas SRT trained twice a week for 35 minutes each session.

Both groups trained for 4 weeks, whereas the CON group maintained normal daily activities. Workouts consisted of 5 exercises: shoulder press, chest press, leg press, low row, and lat pull down. The SRT group completed 1 set of each exercise at 50% 1RM until momentary failure with a 10-second concentric and a 10-second eccentric phase. The TRT group completed 3 sets of 8 repetitions at 80% 1RM for each exercise, with 4 seconds of contraction time for each repetition. 

Researchers found a significant effect on flexibility with the greatest improvements occurring for the training groups (SRT 14.7% and TRT 11%). Both training groups had large percent improvements in strength compared to CON, but only the TRT group reached statistical significance for the strength improvements.

15. A 2014 study, examined the effects of twelve weeks of resistance training with different exercise orders on flexibility levels in elite judo athletes. The results demonstrated the resistance training program increased flexibility levels in all of the joints assessed, independently of the exercise order in athletes.

Therefore, resistance training can provide significant gains in the joint range of motion in judo athletes independently of the exercise order and that gains could be different in other joints.

16. A 2015 study, analysed the effect of resistance training performed at different weekly frequencies on flexibility in older women. For the study,53 older women (>60 years old) were assigned to perform resistance training either two, or three times per week. The resistance training program comprised eight exercises in which the participants performed one set of 10–15 repetitions maximum for a period of 12 weeks. Anthropometric, body-composition, and flexibility measurements were made at baseline and post-study.

The main finding of the present study is that 12 weeks of resistance training was sufficient to increase or at least maintain flexibility in elderly women. In addition, the higher frequency of resistance training induces greater increase in flexibility. 

17. A 2017 study, investigated the effect of resistance training on flexibility of 20 male students, who were divided into two groups: training group & control group. The training group underwent moderate intensity (60-70%) resistance training program for 12 weeks, 3 days/week, 1 session/day. The control group did not undergo any specific training apart from their regular activities. Flexibility was measured by using sit and reach test.

The result of the study revealed that the training group had significant improvement in flexibility among college male hostel students after the resistance training protocol. It was also concluded that, resistance training is one of the best training methods for improving the flexibility as well as the physical fitness of young men.

18. A 2017 study, analysed the effect of resistance training on flexibility in young adult men and women. For the study, 28 men and 30 women underwent resistance training for 16 weeks, 3 times per week. Flexibility measurements were performed at pre-training, mid-training, and post-training.

Researchers found that, both sexes increased flexibility similarly from baseline to mid-training in shoulder extension and lateral trunk inclination. Shoulder flexion increased at same magnitude in men and women from baseline to post-training. Hip flexion and trunk flexion scores increased from baseline to mid-training.

Thus, resistance training improves or at least preserves the flexibility of different joint movements in young adult men and women. In addition, these changes are dependent on the duration of the resistance training program and are not affected by the individuals’ sex.

19. A 2017 study, investigated the effects of six months of resistance training with different number of sets per exercise (one, three, and five sets) on flexibility in men. Forty-seven men were divided into three training groups performing either one set, three sets, or five sets of all exercises in a resistance training session or a control group.

All groups were assessed pre- and post- training for Sit-and-Reach test and range of motion of 10 joints. The training protocol included three weekly sessions and was composed of nine exercises performed at a moderate intensity (eight to 12RM).

The results demonstrated significant differences pre- to post- training for the Sit-and-Reach test for all training groups; however, only the five-sets group showed significant differences when compared to the control group. Thus, the study showed that resistance training results in no negative effects on flexibility.

The researchers concluded by saying that, strength and conditioning coaches and other allied health professionals can expect increases in flexibility when resistance training is performed even without accompanying flexibility training.

20.A 2021 meta-analysis study of RCTs, found that, overall, strength training and stretching were not statistically different in ROM improvements, both in short-term and longer-term protocols. Therefore, if ROM gains are a desirable outcome, both strength training and stretching reveal promising effects.

21. A 2022 systematic review study, reviewed the evidence on benefits of eccentric training for flexibility and strength. The results of 18 studies show that eccentric training is a multi-effective strategy for the lower limb. Not only the magnitude of change but also the amount of significant changes for several flexibility and strength metrics reveal benefits compared to classical strength training. Eccentric training combines both stretching and strengthening in one exercise. In conclusion, especially risk factors like low eccentric strength, flexibility, and ROM can be improved best with eccentric training.

22. A 2023 meta-analysis study, evaluated the effect of chronic resistance training on range of motion compared either to a control condition or stretch training or to a combination of resistance training and stretch training to stretch training. The major findings of this meta-analysis were that resistance training (free weights, machines, Pilates) significantly improves joint ROM.

Furthermore, the beneficial effects of resistance training on ROM were not significantly different from stretch training or the combination of resistance training and stretch training versus stretch training alone. Although both groups improved ROM with resistance training, “untrained and sedentary” individuals had a significantly higher magnitude of ROM change compared with “trained or active people”.

The above studies, clearly busted the “musclebound” or “weight training & inflexibility” myth. The best way to increase your flexibility, and strength is to do heavy resistance training with complete ROM; and add flexibility training to it.