Acute Neuromuscular, Physiological and Performance Responses After Strength Training in Runners: A Systematic Review and Meta-Analysis – Sports Medicine – Open

The objective of this systematic review and meta-analysis was to synthesize the findings in the literature from 1995 to April 2021 regarding the acute effects of ST, in its different modalities (traditional, explosive, plyometrics and concurrent) on neuromuscular, physiological and performance responses in runners. It was verified that performing a ST session, even at high intensity (> 80%RM or 6 RM), with a 24-h interval for a submaximal running session does not change the vertical jump response, physiological respiratory capacity, performance training and submaximal running.

The literature on concurrent training, especially on the effect of aerobic training on ST adaptations, is extensive and well-developed in sports and clinical populations. [1, 38,39,40]. In addition, ST and its neuromuscular and mechanical adaptations already present consolidated knowledge about the benefits in the performance of aerobic modalities [5, 8]. On the other hand, knowledge of the immediate and short-term effects of a ST session on the indirect and directly related variables to running performance is necessary and should be part of the combined training intersection planning.

We hypothesized that session protocols that require higher training load (repetitions, sets, load, execution speed), higher density and proximity to concentric failure generate greater deleterious effects on the subsequent running session [10]. Thus, the hypothesis was partially rejected. The results showed that the variables P_T, DOMS, CK, RPE had a deleterious effect for the experimental group that performed ST. Although it was expected that studies that performed a protocol to promote exercise-induced muscle damage would show this behavior [19,20,21,22], this fact has not been confirmed in plyometrics and traditional training protocols.

As for the outcome of the neuromuscular variables, it is known that the accumulated fatigue after the ST session is due to central factors (reduction in the levels of recruitment of motor units, as well as their activation frequencies) [41], local and peripheral alteration of the structure of the sarcolemma, accumulation of metabolites in the blood flow and ionic imbalance [42]. Consequently, it is expected that there will be changes in the mechanical aspects during the session. Among these variables, high levels of force, such as P_T, measured at fixed angles in isometric action, decreased. As for the CMJ, a variable related to jumping ability, sensitive to fatigue and neuromuscular status [43, 44], with characteristics of dynamic contraction (fast eccentric and concentric phase) in contrast to P_T, it did not present a significant difference. This observation can be justified according to studies that used combined training protocols and traditional intensities of ST (6RM) [31] or ST combined with explosive exercises (30% to 40% of 1RM) [28] in study design with 24 h interval. Suggesting a greater need for recovery following the initial session of lower segments [31]. As for those studies that analyzed P_T, three used EIMD protocols, such as the 10 sets of 10 repetitions at 80% of 1RM in the Smith squat in the study of Burt [19]. This protocol showed higher values in the variables of late muscle pain, swelling and stiffness, caused by disruption of the intracellular structure, sarcolemma, extracellular matrix and impaired muscle function [45].

For lactate levels, no statistically significant difference was observed in the meta-analysis [19, 21, 22, 36, 37]. Changes in La metabolism after an ST sequence do not seem to show consistent results, especially when evaluated during submaximal aerobic exercise. In some studies, the values of this variable did not show statistically significant differences [22, 46], whereas in others, significant differences were observed [47]. De Souza [36] points out that although there was a significant change in La immediately after ST in the two strength protocols used (maximum strength and endurance strength), there was no change after the first km of running (control, maximum strength, and endurance strength (2.7 ± 0.8, 2.7 ± 1.2, and 3.2 ± 1.8 mmolIS·L⁻¹, respectively) even when the run was immediately afterward. Increased blood La level is associated with high intensity exercise due to higher anaerobic metabolism [48, 49], in contrast, it is believed that in the studies evaluated, the runners had a greater predominance of the aerobic zone or resynthesis handsome lactate during submaximal running [50].Ventilatory variables such as VE, VO₂, RER and running economy (RE kcal/min/kg or kJ/min/kg and C_R) were not affected by the previous ST session. The effort of running at a speed corresponding to the oxygen consumption in submaximal efforts (around 55 to 75% of VO₂max) seems not to be affected by the ST session, even in sessions that used EIMD protocols [19, 22]. Other studies that evaluated VO₂ after ST in aerobic modalities such as cycling or cycle ergometer showed no change [47, 51,52,53] in accordance with the result verified in this meta-analysis. The results indicate that the performance of runners after sessions of EIMD and ST seem not to be mediated by cardiorespiratory and metabolic responses to exercise. Mechanical efficiency has been reported as an important determinant of running economy. However, 1 study [37] showed no change in stride length and 3 [20, 28, 39] showed a reduction. Thus, variations in running technique did not favor running economy, further suggesting that any disturbance in this efficiency will subsequently increase aerobic demand [37].

Regarding direct performance measures, few studies have evaluated this variable. Of the selected articles, although statistically different values were observed between the experimental and control groups for speed (km/h) during treadmill running at 1% incline in one study [22]; stride length [19, 28]; and in the time to finish a 5 km run, in absolute values this difference was relevant immediately after the session, but irrelevant after 48 h (20.63 ± 2.42 min before intervention; 22.40 ± 2.86 min after 30 min and 21.26 ± 2.56 min after 48 h) [35].

The exception seems to be in studies that analyzed responses to TTE followed by high-intensity strength sessions (4 × 6RM), in which there was a significant difference with deleterious effects for groups that performed ST concurrently with the running session within 24 h later of the ST session. Doma [30] performed a combined training on the same day: a ST session and, 6 h later, a running session, and applied the TTE the following day (24 h after the ST session and 18 h after the running session). In this case, the high intensity of workload in the ST and the short time between intervention and outcome assessment may have been the main reasons that caused this drop in performance. In the same study, the C_R of the running session was also higher, demonstrating from 6 h deleterious changes in running economy for the group that performed ST.

The present review has the following limitations. Due to the low quantity of studies we were unable to perform a robust analysis of the differences between the effects immediately, and at 6, 10, 24 or 48 h. In general, the main outcome observed was there was a reduction in P_T independent of the evaluation immediately, and at 6, 24 and 48 h [16, 19, 21, 22, 27, 28, 30, 32, 37]. Regarding the other variables, we can still notice a discrepancy between the results, which makes practical implications difficult. For example, in the study by Palmer et al. [37] after ST: 3 × 8RM—bench press; squat; upright row; dead lift; seated row, no changes were observed in VE, HR, La, RPE and stride length after 24 h. In contrast Burt et al. [19] after performing ST: 10 × 10×80% body mass Smith machine showed an increase in the evaluations of CK, DOMS, VO₂, RPE and reduction of stride length after 24 and 48 h. The other variables presented heterogeneous conditions for this evaluation. Furthermore, with the increase in the number of publications on the subject we suggest further studies with a specific population of runners (i.e., recreational or athletes). Some studies proposed different aims and experimental protocols which lead to heterogeneous results. The strengths of this review were the variety of ST protocols added, the sample size, and the reasonable quality of the studies, showing that it is possible for athletic coaches, professionals, and researchers to expect results in line with those presented in this study. It is suggested that more research evaluate direct performance measures, a point considered limited in this study. In addition, studies that use protocols with lower loads, training with body weight and multicomponent strategies are also suggested.

Practical Implications

In summary, although many runners use ST prior to participating in running competitions and during recreational practice, has not been shown to acutely improve performance. This complementary preparation strategy, commonly used to improve neuromuscular adaptation, showed a substantial deleterious effect. So, care to decrease potential muscle damage before competition is recommended. The acute use of ST in combined training programs (i.e., cross training exercises) could be indicated as aerobic benefit and little indicated for immediate performance gains for the runner. Thus, regular (chronic effect) and alternating day ST sessions remain recommended.