Table 2

Intrinsic risk factors for injury

Risk factor	Sport	Sex	Injuries studied	Study type	Effect of risk factor	Ref.
ACL, Anterior cruciate ligament; EPI, epidemiological; PRF, prospective study of potential risk factors; RCT, randomised clinical trials; PNRCS, prospective non-randomised comparative study; n/a, not presented; BMI, body mass index; ROM, range of motion; ITB, iliotibial band; PFPS, patellofemoral pain syndrome.
Age	Soccer	f	All	PRF	Increased incidence in athletes older than 25 (age range studied 14–39)	35
	Soccer	m,f	All	PRF	Increased incidence in athletes older than 14 (age range studied 6–17)	34
	Indoor soccer	m,f	All	EPI	Increased risk in men older than 25, and in girls between 12 and 15 (age range studied 7 to early 50s)	36
	Military training	m,f	All	PRF	Increased risk in men aged 25–35 (age range studied 17–35)	38
	Australian football	n/a	Lower extremity muscle	PRF	Increased incidence of hamstring and calf strain among athletes older than 23; but no difference for quadriceps strains	37
	Australian football, field hockey, basketball, netball	m,f	Lower extremity, back	EPI	Increased incidence 26–30 years (age range studied 9–56)	15
	Soccer	m	All	PRF	Increased incidence in athletes 14–16 years of age v 16–18 years	16
	Basketball	m,f	Ankle	PRF	Increased incidence among younger athletes	22
	Soccer	m	All severe	PRF	No difference in incidence of injury, but injury type differed by age	17
	Soccer	f	Lower extremity	PRF	No association between age and injury	11
	Dancers	m,f	Lower extremity	PRF	No association between age and injury	39
	Netball	f	Lower extremity, back	PRF	No association between age and injury	18
	Track	m,f	Lower extremity, back, stress fractures	PRF	No association between age and injury	40

Gender	Basketball	f	All	PRF	Increased risk of all injuries as a group in females	50
	Soccer	m,f	All	PRF	Increased risk of all injuries as a group in females	34
	Military training	m,f	All	PRF	Increased risk of all injuries as a group in females	38, 51
	Military training	m,f	ACL	EPI	Increased risk of ACL tears in females	42
	European team handball	m,f	ACL	EPI	Increased risk of ACL tears in females	14
	Basketball	m,f	Ankle	PRF	Increased risk of grade I sprain in females; but no difference for grade II, III sprain	19
	Basketball	m,f	All	PRF	Increased risk of all injuries as a group in males and increased risk of knee injury in females	8
	Australian football, field hockey,   basketball, netball	m,f	Lower extremity, back	EPI	Males at increased risk of injury compared with females	15
	Indoor soccer	m,f	All	EPI	No difference in incidence of all injuries, but females had an increased risk of knee injury and males had an increased risk of ankle injury	36
	Track	m,f	Lower extremity, back stress fractures	PRF	No difference in relative risk ;but risk factors were different between males and females	40
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No difference in relative risk; risk factors differed between males and females	53
	32 high school sports	m,f	All	PRF	No association between gender and injury	54
	Dancers	m,f	Lower extremity	PRF	No association between gender and injury	39
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between gender and injury	52

Phase of menstrual cycle	European team handball	f	ACL	PNRCS	Increased risk during week before and after start of menstrual period	14
	n/a	f	ACL	EPI	Increased risk on days 1 and 2 of menstrual period	55
	n/a	f	ACL	EPI	Increased risk during ovulatory phase	56

Previous injury	Soccer	m	All severe	PRF	Increased risk with previous injury	17
	Australian football	n/a	Lower extremity muscle	PRF	Increased risk with previous injury	37
	Dancers	m,f	Lower extremity	PRF	Increased risk with previous injury	39
	Basketball	m,f	Knee	PRF	Increased risk with previous injury	8
	Soccer	m	Ankle and knee	RCT	Increased risk with previous injury	26
	Military training	m	Ankle	PRF	Increased risk with previous injury	20
	Basketball	m,f	Ankle	PRF	Increased risk with previous injury	22
	Volleyball	m,f	Ankle	PCS	Increased risk with previous injury	60
	Basketball	m,f	Ankle	RCT	No association	21
	Soccer	m	Ankle	PRF	No association	61
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association	52

Inadequate rehabilitation	Soccer	m	All	PRF	Increased risk with inadequate rehabilitation of injury	62
	Soccer	m	All severe	PRF	Increased risk with inadequate rehabilitation of injury	17
	Australian football	n/a	Knee - ACL	PRF	Increased risk with inadequate rehabilitation of injury	63

Aerobic fitness	Military training	m,f	All	PRF	Increased risk in recruits with fewer push ups, slower run times, lower Vo₂max and smoking cigarettes	38
	Military training	m,f	All	PRF	Increased risk with slower run times	51
	Soccer	m	All severe	PRF	Increased risk with slower reaction time in response to an optical stimulus	17
	Military training	m,f	Lower extremity	PRF	Increased risk in females with slower run times and increased risk in males with fewer push ups	65
	Netball	f	Lower extremity, back	PRF	Increased risk with greater jump height, cycle work and power	18
	Soccer	f	All	PRF	No association between fitness measures and injury	35
	Military training	m	Ankle	PRF	No association between fitness measures and injury	20

Body size	Soccer	m,f	All	PRF	Increased risk in males of greater height; but no association in females	34
	Australian football	n/a	Lower extremity muscle	PRF	Increased risk with increased height for quadriceps strain; but no association for hamstring and calf strain	37
	Military training	m,f	Lower extremity	PRF	Increased risk with low and high BMI for males and increased risk with shorter height for females	65
	Military training	m	Ankle	PRF	Increased risk with greater (wt × ht²)	20
	Military training	m,f	All	PRF	No association between height, weight, or BMI and injury	38
	American football	n/a	All	PRF	No association between ((wt/ht) × 100) and injury	7
	Soccer	f	All	PRF	No association between BMI and injury	35
	Physical education students	m,f	All	PRF	No association between height, weight, or BMI and injury	66
	Dancers	m,f	Lower extremity	PRF	No association between BMI and injury	39
	Track	m,f	Lower extremity, back stress fractures	PRF	No association between height, weight, lean mass, fat content and injury	40
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between height or weight and injury	52, 53
	Basketball	m,f	Ankle	PRF	No association between height or weight and injury	22

Limb dominance	Soccer	m	All severe	PRF	No association of ankle or non-contact knee injury; but increased incidence of contact knee injuries in dominant leg	17
	Soccer	m	All	PRF	Increased risk of ankle injury in dominant leg; but no association of muscle strain	67
	Australian football	n/a	Lower extremity muscle	PRF	Increased quadriceps strain in dominant leg; but no association with hamstring or calf strain	37
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	Increased incidence in left leg dominant	52
	European team handball	m	All	PRF	No association between limb dominance and injury	6
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between limb dominance and injury	53
	Soccer	m	Ankle	RCT	No association between limb dominance and injury	26

Generalized joint laxity	Soccer	f	All	PRF	Increased risk with increased laxity	35
	Soccer	f	Lower extremity	PRF	Increased risk of trauma with increased laxity; but no association between overuse injury and generalized laxity	11
	All collegiate sports	m,f	Lower extremity	PRF	No association in females; but increased risk with decreased laxity in males	68
	American football	m	All	PRF	No association between generalized laxity and injury	70
	Netball	f	Lower extremity, back	PRF	No association between generalized laxity and injury	18
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between generalized laxity and injury	52, 53

Joint specific laxity	Soccer	m	All	PRF	Increased risk of knee injury with increased medial knee laxity; but no association between ankle laxity and ankle injury	30
	Soccer	m	All	PRF	Increased risk of all injuries as a group with increased knee laxity	67
	Soccer	m	All severe	PRF	Increased risk of ankle and knee injury with increased joint laxity	17
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	Increased risk with greater talar tilt exam in males; but no association in females	53
	American football	m	Ankle	PRF	Increased risk with greater talar tilt exam	71
	Basketball	m,f	Ankle	RCT	No association between ankle laxity and injury	21
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between ankle laxity and injury	52

Muscle tightness	Military training	m	All	PRF	Increased risk with high and low levels of hamstring tightness	38
	Military training	m	Lower extremity	PRF	Increased risk of Achilles tendinitis with increased gastrocnemius tightness	73
	All collegiate sports	m,f	Lower extremity	PRF	No association between muscle tightness in females and increased risk of injury with greater tightness in males	68
	Basketball	m,f	Ankle	PRF	Increased risk with improper stretch, warm up	22
	Soccer	m	All	PRF	No association between muscle tightness and injury	30

Range of motion	Soccer	f	Lower extremity	PRF	Increased risk with increased knee hyperextension and increased risk of overuse injury with right/left differences in ankle ROM and hamstring flexibility	11
	Military training	m	Lower extremity	PRF	Increased risk of Achilles tendinitis with greater inversion, but no association with eversion/inversion and stress fractures	73
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	Increased risk with increased eversion in females, but no association between ROM and injury in males	53
	Physical education students	m,f	All intramural	PRF	No association between ROM and injury	66
	Dancers	m,f	Lower extremity	PRF	No association between ROM and injury	39
	Basketball	m,f	Ankle	RCT	No association between ROM and injury	21
	Military training	m	Ankle	PRF	No association between ROM and injury	20

Muscle strength, imbalance	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	Increased risk with ankle strength imbalances	52
	Soccer	f	Lower extremity	PRF	Increased risk of trauma with low hamstring to quadriceps ratio and increased risk of overuse with high hamstring to quadriceps ratio	11
	Soccer	m	All	PRF	Decreased quadriceps strength on injured side compared with uninjured	67
	Soccer	f	All	PRF	No association between quadriceps and hamstring strength and injury	35
	Military training	m	Ankle	PRF	No association between quadriceps strength and injury	20
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between ankle strength and injury	53

Muscle reaction time	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between reaction time and injury; trend for injury in females with slower tibialis anterior and faster gastroc reaction time to dorsi flexion perturbation	53

Limb girth	Track	m,f	Lower extremity, back stress fractures	PRF	Increased risk with smaller calf girth in females; but no association in males, and no association of thigh girth in males or females	40
	Basketball	n/a	Lower extremity	PRF	Increased risk of injury with greater right/left difference in thigh girth	75
	Military training	m	Ankle	PRF	Increased risk of ankle injury with increased calf girth and no association between thigh girth and injury	20

Postural stability	Basketball	m,f	Ankle	PRF	Increased risk with increased sway (e.g. diminished balance)	76
	Soccer	m	Ankle	PRF	Increased risk with increased sway (e.g. diminished balance)	77
	Soccer	f	Lower extremity	PRF	Increased risk with increased sway (e.g. diminished balance)	11
	Netball	f	Lower extremity, back	PRF	No association between postural sway and injury	18
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between postural sway and injury	53

Anatomical alignment	All high school	m.f	ACL	PRF	Increased risk with narrower femoral intercondylar notch width	79
	Football, ice hockey, basketball	m,f	ACL	PRF	Increased risk with narrower femoral intercondylar notch width	80
	soccer, gymnastics, volleyball
	Military training	m	Lower extremity	PRF	Increased risk with tibial valgum, increased Q angle	81
	Basketball	n/a	Lower extremity	PRF	Increased risk with greater side to side differences in Q angle, rearfoot valgus and leg length discrepancy	75
	Runners	m,f	Lower extremity overuse	PRF	Increased risk of shin injuries with greater tubercle-sulcus angle and knee varus and increased risk of all overuse with decreased leg length difference	82
	Military training	m	Ankle	PRF	Increased risk with increased leg length, foot length, foot width; and no association between tibial varum/valgum, hip external/internal rotation or tibia length and injury	20
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	Increased risk in females with increased tibial varum; but no association in males	53
	Physical education students	m,f	All	PRF	No association of hip, knee, rearfoot alignment or leg length and injury	66
	Soccer	f	Lower extremity	PRF	No association of Q angle and injury	11

Foot Morphology	Military training	m	Lower extremity	PRF	Increased risk of stress fractures with high arches	84
	Military training	m	Lower extremity	PRF	Foot and knee overuse injury associated with increased arch height	86
	Military training	m	Lower extremity	PRF	Increased risk of stress fractures with pes planus or cavus foot types; but no association between incidence of ITB syndrome or PFPS and foot type	73
	Football, cross country	m,f	Knee, ankle	PRF	Knee pain associated with pronated or supinated foot types; but no association with ankle sprain	85
	Runners	m,f	Lower extremity, back	PNRCS	Lateral, bony, foot/ankle injury associated with high arches and medial, soft tissue, knee injury associated with low arches	87
	Physical education students	m,f	All	PRF	No association between arch index and injury	66
	Runners	m,f	Lower extremity overuse	PRF	No association between arch index, heel valgus and injury	82
	Soccer, field hockey, lacrosse	m,f	Ankle	PRF	No association between foot type and injury	53
	Basketball	m,f	Ankle	RCT	No association between foot type and injury	21