Table 2

Univariate RR to sustain a future HSI using BFlh fascicle length, muscle thickness, eccentric strength, MVIC strength, between-limb imbalances of these variables, previous injury history and demographic data as risk factors

Risk Factor	n	Percentage from each group that sustained a HSI	RR (95% CI)	p Value
Passive fascicle length	152
<10.56 cm	56	33.9	4.1 (1.9 to 8.7)	0.001**
≥10.56 cm	96	8.3
Passive fascicle length relative to BFlh length	152
<0.254	38	39.4	3.7 (1.9 to 7.3)	0.001**
≥0.254	114	10.5
25% MVIC fascicle length	141
<9.61 cm	79	25.3	3.2 (1.2 to 7.9)	0.008*
≥9.61 cm	62	8.0
Passive fascicle length imbalance	152
<10% imbalance	80	16.3	1.2 (0.6 to 2.4)	0.673
≥10% imbalance	72	19.4
<15% imbalance	99	15.1	1.5 (0.7 to 3.0)	0.271
≥15% imbalance	53	22.6
<20% imbalance	125	16.8	1.3 (0.6 to 3.0)	0.579
≥20% imbalance	27	22.2
25% MVIC fascicle length imbalance	141
<10% imbalance	78	20.0	1.3 (0.6 to 2.6)	0.512
≥10% imbalance	63	20.6
<15% imbalance	100	22.7	0.7 (0.3 to 1.7)	0.630
≥15% imbalance	41	14.6
<20% imbalance	118	22.0	0.4 (0.1 to 1.7)	0.249
≥20% imbalance	23	8.7
Passive muscle thickness	152
<2.35 cm	36	11.1	0.56 (0.2 to 1.5)	0.320
≥2.35 cm	116	19.8
25% MVIC muscle thickness	141
<2.61 cm	58	20.6	1.3 (0.6 to 2.7)	0.504
≥2.61 cm	83	15.6
Eccentric strength	131
<337 N	96	25.0	4.4 (1.1 to 17.5)	0.013*
≥337 N	35	5.7
<145 Nm	89	25.8	3.6 (1.2 to 11.4)	0.017*
≥145 Nm	42	7.1
<4.35 N/kg	82	25.6	2.5 (1.1 to 6.2)	0.041*
≥4.35 N/kg	49	10.0
<1.86 Nm/kg	78	26.9	2.9 (1.1 to 7.1)	0.011*
≥1.86 Nm/kg	53	9.4
Eccentric strength imbalance	131
<10% imbalance	76	19.7	1.0 (0.5 to 2.0)	1.000
≥10% imbalance	55	20.0
<15% imbalance	98	18.3	1.3 (0.6 to 2.7)	0.459
≥15% imbalance	33	24.2
<20% imbalance	117	18.8	1.5 (0.6 to 3.8)	0.476
≥20% imbalance	14	28.5
MVIC strength	141
<400 N	93	21.5	2.0 (0.8 to 5.2)	0.161
≥400 N	48	10.4
<172 Nm	88	20.4	1.5 (0.7 to 3.5)	0.364
≥172 Nm	53	13.2
<4.60 N/kg	52	23.1	1.5 (0.7 to 3.2)	0.254
≥4.60 N/kg	89	14.6
<2.07 Nm/kg	62	22.6	1.6 (0.8 to 3.3)	0.192
≥2.07 Nm/kg	79	13.9
MVIC strength imbalance	141
<10% imbalance	81	19.7	0.8 (0.4 to 1.8)	0.826
≥10% imbalance	60	16.6
<15% imbalance	110	16.3	1.3 (0.6 to 2.9)	0.434
≥15% imbalance	31	22.6
<20% imbalance	126	17.4	1.1 (0.4 to 3.3)	0.732
≥20% imbalance	15	20.0
Prior injury	152
HSI	30	30.0	2.0 (1.0 to 4.0)	0.063
No HSI	122	14.7
ACL	16	31.1	1.9 (0.8 to 4.4)	0.164
No ACL	136	16.1
Calf strain	13	23.1	1.3 (0.4 to 3.8)	0.713
No calf strain	139	17.3
Quadriceps strain	21	28.6	1.8 (0.8 to 3.9)	0.215
No Quadriceps strain	131	16.0
Chronic groin pain	13	23.1	1.3 (0.5 to 3.8)	0.703
No chronic groin pain	139	17.3
Age (years)	152
≤18.0	8	12.5	1.5 (0.2 to 9.7)	1.000
>18.0	144	18.7
≤20.4	37	2.7	8.4 (1.1 to 59.5)	0.005*
>20.4	115	22.6
≤23.7	74	6.7	4.2 (1.6 to 10.4)	0.001*
>23.7	78	28.2
≤28.8	116	13.8	2.2 (1.1 to 4.3)	0.043*
>28.8	36	30.5
≤32.6	136	12.5	0.7 (0.2 to 2.6)	0.739
>32.6	16	18.4
Height (cm)
≤182.3	111	15.3	1.6 (0.8 to 3.4)	0.206
>182.3	41	24.4
Weight (kg)
≤77.9	102	15.7	1.4 (0.7 to 2.8)	0.370
>77.9	50	22.0

*=p<0.05, **=p<0.001 when comparing the RR of future HSI between groups.ACL, anterior cruciate ligament; BFlh, biceps femoris long head; Cm, centimetres; HSI, hamstring strain injury; Kg, kilogram; MVIC, maximal voluntary isometric contraction; N/Kg, Newtons per kilogram of body weight; N, Newtons; Nm/kg, Newton metres per kilogram of body weight; Nm, Newton metres; RR, relative risk.