Objective The purpose of this study was to investigate the association between ankle plantar-flexor muscle (PF) strength and balance and walking speed in healthy adults. Methods Four databases (Ovid MEDLINE, Ovid EMBASE, CINAHL Plus, and SPORTDiscus) were searched from inception until December 2019. Studies with any design were included if the association between PF strength and balance and walking speed was investigated among healthy adults. Articles were screened for eligibility independently by two reviewers. Study characteristics and Pearson r values derived from the association between PF strength and balance and walking speed were extracted. Thirty-four studies were eligible. The main group of interest in the studies was older adults. Pearson r values were transformed to rz values using Fisher z-transformation. Meta-analysis of rz values was conducted and then back-transformed to r. Results In older adults, PF maximal isometric strength had a positive weak association with static balance (r = 0.20; 95% CI = 0.08–0.32), a positive moderate association with dynamic reactive balance (r = 0.42; 95% CI = 0.32–0.57) and proactive balance (r = 0.55; 95% CI = 0.18–1.06), and a positive weak association with preferred walking speed (r = 0.29; 95% CI = 0.19–0.41), and maximum walking speed (r = 0.34; 95% CI = 0.06–0.63). In younger adults, there was a moderate association between early phase PF rate of torque development and reactive balance (0.42 < r < 0.52). Conclusions PF strength appears to moderately be associated with dynamic reactive and proactive balance and weakly associated with static balance and walking speed. This finding highlights the potential role of PF strength in dynamic reactive and proactive balance.

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Background/Aims Proprioception acuity is important in sports activities and stretching is widely used in warm-up programmes. The main objective of this study was to evaluate if a warm-up programme with and without stretching flexors and extensors muscles could affect knee joint position sense. Methods The effects of different stretching regimens on joint position sense were examined. A total of 12 semi-professional football players completed four warm-up sessions over 4 weeks: standard warm-up programme; standard warm-up programme with quadriceps stretching; standard warm-up programme with hamstring stretching; and standard warm-up programme with stretching of both quadriceps and hamstrings. Open kinetic chain knee joint position sense was estimated from the ability to reproduce the three target angles (20°, 45° and 60° knee flexion) in the dominant limb before and after the intervention. Results In the absolute angular error, there was a statistically significant three-way interaction between the warm-up programme, target angle and time (F (6, 54)=6.88, P=0.001). Findings of post-hoc analysis demonstrated that there was a statistically significant difference between the pre- and post-stretching of hamstrings for the target angles of 20° (4.70 vs 1.57, P=0.01), 45° (1.70 vs 4.50, P=0.02), and 60° (1.93 vs 4.20, P=0.02). In the relative angular error, interaction of time by the warm-up programme was significant (F (3, 27)=3.41, P=0.03). Conclusions The warm-up programme with static stretching of hamstrings had a negative effect on open kinetic chain knee joint position sense during the flexion to extension repositioning task, which may not only have a negative effect on performance of athletes as a part of warm-up exercises, but may also lead to further injuries.