Of the 210 limbs evaluated, 58 were left-dominant and 152 were right-dominant. The total of HSIs in the last 2 years were 46 limbs: 37 without recurrence, 7 had one recurrence and only one had 2 recurrences. The period between injury and testing was 12.03 ± 6.6 months (range: 2–19 months). The time loss for limbs with only one injury was 24.1 ± 17.1 days and for the limbs with recurrence it was 22.2 ± 15.4 days. Six players (n = 12) who had injuries in both limbs were excluded in all the statistical comparisons since sprint performance and therefore load sharing patterns could differ between players with one previously injured limb and both previously injured limbs. Therefore, 34 previously injured limbs were analyzed, with the most affected muscle being the BFlh with 14 injuries, followed by the SM with 6 and the ST with 3, while 11 injuries could not be attributed to a specific muscle.
Large elastography map areas were obtained in both the passive (BFlh: 4.3 ± 0.9 cm2; BFsh: 4.0 ± 1.0 cm2; SM: 3.7 ± 0.9 cm2; and ST: 5.4 ± 0.6 cm2) and active (BFlh: 5.5 ± 0.6 cm2; BFsh: 5.6 ± 0.7 cm2; SM: 4.7 ± 0.9 cm2; and ST: 5.7 ± 0.6 cm2) shear modulus. Additionally, the elastogram window filling was very high in both passive (BFlh: 99.8 ± 0.5%; BFsh: 99.9 ± 0.4%; SM: 99.8 ± 0.4%; and ST: 99.9 ± 0.8%) and active (BFlh: 98.8 ± 2.5%; BFsh: 98.3 ± 2.6%; SM: 97.1 ± 3.5%; and ST: 99.6 ± 0.9%) shear modulus. In pre-task conditions, the passive shear modulus SEM obtained for each muscle was the following: BFlh: 0.35 kPa, BFsh: 0.45 kPa, SM: 0.65 kPa, and ST: 0.31 kPa, while the active shear modulus SEM of each muscle was: BFlh: 4.33 kPa, BFsh: 9.03 kPa, SM: 4.75 kPa, and ST: 5.98 kPa. After the sprint task, the passive shear modulus SEM of each muscle was: BFlh: 0.56 kPa, BFsh: 0.60 kPa, SM: 0.45 kPa, ST: 0.32 kPa, while the active shear modulus SEM was: BFlh: 6.15 kPa, BFsh: 9.33 kPa, SM: 4.96 kPa, ST: 7.12 kPa.
A significant effect in the average sprint speed was seen for both groups of players (fastest: 7.07 ± 0.33 m/s; slowest: 6.68 ± 0.33 m/s; p < 0.001; η2p = 0.084) and for the interaction sprint 𝗑 age (p = 0.031; η2p = 0.031) however, no significant interaction was found for injury 𝗑 sprint (p = 0.509; η2p = 0.008). A significant effect was found for age (p = 0.002; η2p = 0.284), however no significant differences were seen between players with and without injury history (p = 0.284; η2p = 0.012) (Fig. 1).
In relation to the comparison involving limbs with and without injury history with age as covariate (Table 1), passive shear modulus BFlh (pre: 4.39 ± 0.79 kPa; post: 4.37 ± 0.74 kPa; p = 0.011, η2p = 0.067) and ST (pre: 4.59 ± 0.69 kPa; post: 4.21 ± 0.69 kPa; p < 0.001; η2p = 0.216) showed significant differences between instants, and demonstrated significant effect for the covariate age for both, BFlh (p = 0.007; η2p = 0.075) and ST (p = 0.009; η2p = 0.071). Moreover, in active shear modulus, the BFlh (pre: 31.73 ± 10.43 kPa; post: 31.99 ± 12.28 kPa; p = 0.012; η2p = 0.064) and SM (pre: 35.62 ± 11.18 kPa; post: 35.56 ± 11.39 kPa; p = 0.050; η2p = 0.040) showed a significant difference between instants. Finally, the BFlh/MH ratio reported significant differences between instants (pre: 0.37 ± 0.30 kPa; post: 0.36 ± 0.20 kPa; p = 0.039; η2p = 0.045). Regarding mechanical parameters, significant differences between instants was only seen for TU-RTDmax (pre: 78.88 ± 25.51 ms; post: 76.11 ± 23.35 ms; p = 0.003; η2p = 0.087) and respectively interaction of instant 𝗑 age (p = 0.004; η2p = 0.083).
The comparison between limbs with BFlh injury history and healthy control limbs (Table 2), showed significant differences pre vs post only in passive shear modulus of BFsh (pre: 6.71 ± 0.90 kPa; post: 6.34 ± 0.83 kPa; p = 0.014; η2p = 0.243) and ST (pre: 4.68 ± 0.69 kPa; post: 4.28 ± 0.58 kPa; p < 0.001; η2p = 0.407). For the mechanical parameters, a decrease in PT (pre: 137.15 ± 23.65 Nm; post: 125.92 ± 20.84 Nm; p < 0.001; η2p = 0.446), RTD 50–100 (pre: 0.80 ± 0.16 ms; post: 0.74 ± 0.15 ms; p = 0.007; η2p = 0.251) were seen between instants. Moreover, a significant interaction injury 𝗑 instant was seen for RTD 0–50 (p = 0.024; η2p = 0.181).
With respect to the comparison involving limbs with injury history and their healthy contralateral limb (Table 3), in passive shear modulus the BFsh (pre: 6.87 ± 1.24 kPa; post: 6.52 ± 0.89 kPa; p = 0.018, η2p = 0.169) and ST (pre: 4.47 ± 0.48 kPa; post: 4.10 ± 0.64 kPa; p < 0.001, η2p = 0.395) showed a significant difference between instants. For active shear modulus only a significant interaction between sprint instants and limbs with or without injury history was seen for ST (p = 0.003; η2p = 0.241). For mechanical parameters, significant differences were seen for PT (pre: 139.75 ± 29.04 Nm; post: 128.24 ± 28.04 Nm; p < 0.001; η2p = 0.535) and RTD 50–100 (pre: 0.81 ± 0.23 N/ms; post: 0.74 ± 0.20 N/ms; p = 0.006; η2p = 0.207) between instants. Furthermore, a significant injury 𝗑 instant interaction was seen for RTD 150–200 (p = 0.028; η2p = 0.138).
Concerning the comparison involving limbs with BFlh injury history and their healthy contralateral limb (Table 4), in passive shear modulus the ST (pre: 4.49 ± 0.55 kPa; post: 4.05 ± 0.59 kPa; p = 0.001, η2p = 0.671) presented a significant difference between instants. Additionally, in active shear modulus the BFsh (pre: 49.44 ± 12.34 kPa; post: 55.19 ± 15.60 kPa; p = 0.034; η2p = 0.348) showed a significant difference between instants, while the ST demonstrated a injury 𝗑 instant interaction (p = 0.036; η2p = 0.318). Finally, for mechanical parameters, a statistical difference was observed between instants for PT (pre: 141.04 ± 37.81 Nm; post: 133.45 ± 33.32 Nm; p = 0.012; η2p = 0.396), RTD 0–50 (pre: 0.40 ± 0.19 N/ms; post: 0.47 ± 0.20 N/ms; p = 0.015; η2p = 0.379), and TU-RTDmax (pre: 81.84 ± 21.39 ms; post: 73.16 ± 16.73 ms; p = 0.019; η2p = 0.354). RTD 0–50 also presented a significant difference between limbs with BFlh injury history and their contralateral with no injury history (previously injured: 0.48 ± 0.21 N/ms; contralateral: 0.40 ± 0.18 N/ms; p = 0.005; η2p = 0.469).