Flexibility training is a key component in exercise programs with the goal to develop quality of life and health. 1,2 Static stretching (SS) is one of the methods often adopted to improve the range of motion temporarily. 3 However, several studies have shown that pre-exercise stretching induces significant reductions on force production when compared to resistance exercises performed isolated. 4–7 This phenomenon has been named the stretching-induced force deficit. 8

Adequate biomechanical performance of lower-body resistance exercises in health and/or sport conditioning programs requires a high level of range of motion. 9 Appropriate joint flexibility not only permits proper form, but also allows the trainee the ability to work against resistance through a full range of motion. 10 However, SS adopted prior to resistance training (RT) can induce significant decreases on muscle endurance, 2,4 torque 10,11 and power performance. 7 Two primary hypotheses have been proposed to explain the stretching-induced force deficit. The first hypothesis is associated to a neural factor, causing a decrease in muscle activation and reflex sensitivity. 12 The second hypothesis involves a mechanical factor, promoting a decrease in stiffness of the muscle-tendon unit (MTU) that may affect the muscle's length–tension relationship. 13 On the other hand, there are limited evidences about the time course of the stretching-induced force deficit between SS and resistance exercises.

Fowles et al. 14 observed decreases of 28% on maximal voluntary isometric contraction (MVIC) of triceps surae after SS, and they also found a reduction of 9% after 1 h. McBridge et al. 15 observed significant reduction in MVIC, 1, 2, 8 and 16 min after SS. This data indicated that negative effect induced by SS on strength performance has a time course relationship, and it is probably associated to the volume (duration and number of sets) of stretching and the target muscle group. On the other hand, there is a lack of evidences about the effect of different intervals between SS and resistance exercises on repetition performance.

Furthermore, previous evidences suggested that pre-exercise stretching may not prevent injuries or improve athletic and/or stretching performance. 10,16 However, coaches and practitioners usually adopted stretching exercises before RT with the goal optimize the training sessions durations. For this reason, evidences about exercise models which SS and resistance exercises could be applied in the same exercise session, may be positive and also helps conditioning professionals and practitioners to improve the outcomes without compromising the strength performance.

Therefore, the purpose of this study was to investigate the effect of different intervals between passive SS for hip adductors, quadriceps and hamstring muscles and the repetition performance of resistance exercises for lower body muscles over multiples sets.

Excellent day-to-day 10-RM workload reliability for each exercise was shown by this protocol. The intra-class correlation coefficients (ICC) for the group were LA (ICC = 0.91), LE (ICC = 0.93) and LC (ICC = 0.94). The paired t test did not show any difference between tests and retest loads for each resistance exercise (p < 0.05).

Total training volume (repetitions × sets × exercises) was calculated for LE, LC and HA for each experimental protocols. Significant differences were observed between exercises and sequences (p = 0.0001) for total training volume. Training volume under P30 (84.55 ± 1.68) was significantly higher than P15 (79.73 ± 1.89; p = 0.001) and PWI (68.09 ± 2.03; p = 0.0001), respectively. Significant differences were also noted under P15 compared to PWI (p = 0.03). Significant interactions were noted between repetitions and sets for total work (p = 0.002). Total work (repetitions × sets) was higher for LE exercise, under P30 compared to P15 (p = 0.0001) and PWI (p = 0.002), respectively (Fig. 1). This was also true for LC and HA exercises which showed higher total work under P30 compared to P15 (p = 0.0001; p = 0.002) and PSI (p = 0.0001; p = 0.0001), respectively. Significant differences were also observed between P15 and P30 for LE (p = 0.031), LC (p = 0.002) and HA (p = 0.0001).

Fig. 1.

(0.06MB).

Total work (repetitions × sets) of each exercise in PWI, P15 and P30 protocols. *: Significant difference for P15; †: significant difference for P30; PWI: RT session performed immediately after SS exercises; P15: fifteen minute interval between SS and RT; P30: thirty minute interval between SS and RT. SS: static stretching; RT: resistance training.

The numbers of repetitions performed per set for each exercise over the experimental protocols are presented as mean and standard deviation in Table 1. A lower number of repetitions performed over the three sets were noted for LE, LC and HA exercises, under PWI compared to P15, except for set 1 of LC, and set 1 and 2 of HA. Similar results were found for all sets when compared to P30, except for the set 2 and 3 of HA. No differences were found between P15 and P30 conditions.

The purpose of this study was to clarify the time course of a stretching-induced decrease in repetition performance of lower body exercises. The main finding of the present investigation were the lower number of repetitions performed over the three sets immediately after SS exercises (PWI) when compared to the protocols which were adopted 15 (P15) and 30 min (P30) intervals between SS and RT sessions for LE, LC and HA exercises, respectively. These findings are in agreement with previous studies which observed significant decreases on force production immediately after SS. 2,4,10,22

Marek et al. 20 also found a decrease in muscle activation, peak torque and isokinetic strength during LE performed immediately after four SS exercises and proprioceptive neuromuscular facilitation exercises for quadriceps muscles. Cramer et al. 11 also observed a significant reduction in peak torque during LE exercise at fast and slow speeds after four SS exercises for the quadriceps muscles. However, in the current study, there were significant increases in total training volume performed per set adopting 15-minute (16.1%) or 30-minute (24.2%) interval between SS and resistance exercises compared to the protocol without interval (PWI). These results suggested that progressive intervals between SS and RT exercises may avoid the negative effects induced by stretching exercises on repetition performance for lower body exercises.

Fowles et al. 14 investigated the MVIC of ankle extensors after 30 min of SS and found significant reduction of 28% that persisted for approximately 60 min after the stretching. Similar results were found by McBride et al. 15 who observed significant reduction in MVIC even after 1, 2, 8 and 16 min of rest interval after three sets with 30 s of SS on quadriceps muscles. However, the authors observed that 30 min after the protocols the MVIC levels returned to control values. Power et al. 7 also observed a significant reduction in peak torque and MVIC of the knee extensors 60, 90 and 120 min after performed six SS exercises for quadriceps, hamstrings and ankle extensors. However, in the current study, intervals between 15 and 30 min after SS avoided significant decreases in repetition performance during LE, LC and HA exercises compared to PWI. Some peripheral mechanisms have been proposed to explain the reduced muscle activation after stretching as follows: (a) autogenic inhibition of the Golgi tendon reflex, 12 (b) mechanoreceptors and nociceptors, 4 (c) fatigue-induced inhibition, 21 (d) joint pressure feedback inhibition because of excessive ranges of motion during stretching, 23 and (e) stretch reflex inhibition originating from the muscle spindles. 10

However, previous studies found opposite results to those observed in the current study associated to PWI. Behm et al. 24 found that 135 s of SS exercises for quadriceps and hamstring did not cause significant changes on strength performance. Gomes et al. 4 found that three sets with 30 s of SS on pectoralis major and quadriceps muscles promoted no significant difference in the number of repetitions completed in the bench press and LE exercises with 40, 60 and 80% 1RM. Ogura et al. 5 also adopted 30 s of SS and observed no reduction in MVIC during LE and LC. According to Franco et al. 2 the volume (duration) of the SS is one of the factors that may be responsible for the deleterious effect on the force production. These evidences leaving in doubts the influence of the SS duration on subsequent RT exercise performance.

Furthermore, in the present study, intervals between 15 and 30-minutes showed a higher number of repetitions performed when compared to the protocol without rest intervals between SS and RT. These data indicated that longer intervals between the SS and RT may be an important variable when flexibility and RT are performed in the same training session. The major contributor of the stretching-induced force deficit is unclear (i.e., either a neural factor or mechanical factor). McHugh and Cosgrave 25 considered that it may be easier to initiate a neural affect than a viscoelastic effect. These hypotheses may justify the significantly lower repetition performance observed in the current study during PWI. In contrast, several previous studies have indicated that neural effects are more transient 8 or play a smaller 23 in the stretching-induced force deficit. 3,9,10,26,27 Therefore, the potential mechanisms underlying the stretching-induced force deficit are not completely understood, and further study has been encouraged to clarify.

Nevertheless, others factors might be responsible for the acute response of stretching on muscle contractibility. Fowles et al. 14 concluded in their study that the decrease on force production was associated with a reduction in motor unit recruitment and activation of Golgi tendon organs. McBride et al., 15 the prolonged stretching of the fibers determines accommodation in order to compromise the transmission of motor recruitment, inducing muscle strain in plastic components and reducing the muscle tension. It is noteworthy that in the aforementioned studies was not specified if individuals performed flexibility training frequently. Decreased amplitude of surface EMG during MVCs after static stretching provides evidence that the stretching-induced force deficit is attributable to a neural effect. 13,28

A secondary finding of the current study in the significant reductions in the number of repetitions noted set per set for all exercises and protocols. These data suggested that 1-minute of rest interval was inadequate to maintain the total work over the three experimental protocols. This is also in agreement with previously findings reported such as, the study of Miranda et al. 29 who found a significant reduction in the number of repetitions per sets using 1-minute compared to 3-minutes rest intervals three sets with 8RM loads for upper and lower body exercises. These data indicated that the rest interval adopted in the current research did not allow a complete level of physiological recovery (i.e., resynthesis of intramuscular phosphocreatine and adenosine triphosphate and removal of detrimental metabolites) adequate to maintain the strength performance. 30

One of the limitations of the current study was associated to the SS protocol adopted that was carried out through one exercise for quadriceps, hamstrings and hip adductor, whereas, in previous studies multiples stretching exercises were applied for the same muscle group. 4,8,9,28 However, the results of the current study may help coaches and RT practitioners, considering that flexibility and RT are usually performed in the same training session.

In conclusion, significant greater repetition performance was noted adopting 30-minute rest interval between SS and RT, when compared to 15-minute and RT performed immediately after stretching. Similar results were observed between P15 and PWI for lower body exercises. Therefore, SS may promote reduction in repetition performance which can last after 15-minute post stretching. Thus, SS may be avoided prior to RT session for lower limb exercises.

The authors report no conflicts of interest.