Rapid Ham/Quad Strength in ACL-Reconstructed Ski Racers
Rapid Ham/Quad Strength in ACL-Reconstructed Ski Racers
Purpose Because of the importance of hamstrings (HAM) and quadriceps (QUAD) strength for anterior cruciate ligament (ACL) injury prevention and the high incidence of ACL injury in ski racing, HAM and QUAD maximal and explosive strength were assessed in ski racers with and without ACL reconstruction (ACL-R).
Methods Uninjured (n = 13 males, n = 8 females) and ACL-R (n = 3 males, n = 5 females, 25.0 ± 11.3 months after operation) elite ski racers performed maximal voluntary isometric HAM and QUAD contractions to obtain maximal torque (MVC) and rate of torque development (RTD) at 0–50, 0–100, 0–150, and 0–200 ms. MVC and RTD (per kilogram body mass) were calculated for the uninjured group to compare between sexes and to compare the control group with the ACL-R limb and unaffected limb of the ACL-R skiers. HAM/QUAD MVC and RTD strength ratios (H/Q ratios) were also compared.
Results The ACL-R limb demonstrated significant HAM and QUAD deficits compared with the contralateral limb for MVC and late-phase RTD (P < 0.05). Uninjured male skiers also displayed a limb difference for HAM MVC and RTD at 150 ms (P < 0.05). QUAD MVC and RTD deficits were observed in the affected limb of ACL-R skiers, which led to an inflated H/Q ratio (50 ms) compared with that in uninjured controls (P < 0.05). Compared with male skiers, females displayed greater relative HAM RTD (50 ms) and an elevated H/Q RTD ratio (50 ms), suggesting enhanced ACL protection (P < 0.05).
Conclusions Because of the strength demands of ski racing, our results suggest the importance of including HAM and QUAD strength assessments in the physical evaluation of uninjured skiers. Furthermore, HAM and QUAD strength should be assessed over a long-term period after surgery to identify chronic strength deficits in ACL-R ski racers.
Elite alpine ski racing is a physically demanding sport involving high speeds and large external loads imposed on the lower limbs that occur in an unpredictable environment. Skiers perform repeated bidirectional turns with forceful eccentric muscle contractions, which typically involve maximal levels of neuromuscular activity in the thigh muscles. To meet these demands, elite alpine ski racers display high levels of hamstrings (HAM) and quadriceps (QUAD) strength, an elevated HAM/QUAD strength ratio (H/Q ratio), and marked bilateral strength symmetry.
Because of the extreme demands of elite alpine ski racing, there is a high risk for lower body injury, especially to the knee joint. In a competitive season, knee injuries accounted for over 30% of the injuries experienced by elite alpine ski racers, and more than half of these injuries resulted in a significant time loss from sport (>28 d). Anterior cruciate ligament (ACL) rupture is the most common form of serious knee joint injury in ski racing, accompanied by a high ACL reinjury rate. Research into the mechanisms and etiology of noncontact ACL injury in elite alpine ski racing highlights distinct differences compared with ACL injury in field sports, including several mechanisms of high-force injury. Furthermore, at the elite level, no sex differences in ACL injury rates are found, which is attributable to the preclusion of sex-related risk factors due to the high force/energy injury mechanisms.
To achieve effective injury prevention, it is important to identify modifiable risk factors that can be targeted through exercise and training. However, to date, only a single scientific study has been conducted that was aimed at assessing the relationship between modifiable (trainable) risk factors and ACL injury in ski racers, suggesting that core strength deficits were associated with injury in young competitive ski racers. However, more senior elite ski racers may be at an even greater risk for ACL injury. Not only is there a paucity of scientific literature on trainable risk factors for ACL injury prevention in elite alpine ski racers, but also, there are no studies on ACL reinjury prevention in actively competing ski racers with a history of ACL injury and ACL reconstruction (ACL-R).
After ACL injury, the primary objective is to restore QUAD and HAM muscle strength. Thigh muscle strength deficits have been associated with a successful return to sport and activity. Restoring thigh muscle strength is especially important for ACL-R ski racers because of the importance of QUAD strength in ski racing and the influence of HAM/QUAD strength imbalance on knee injury risk. However, long-term HAM and QUAD strength deficits often persist despite rehabilitation, and because coordinated HAM and QUAD muscle function is important for ACL protection, identifying strength deficits is important.
Several measures of HAM and QUAD muscle strength have been proposed for their clinical efficacy. However, because of the short time history of noncontact ACL injury in field sports (<50 ms after foot contact), the assessment of maximal HAM and QUAD strength, which often requires more than 300 ms to develop under isometric conditions, has been questioned. Instead, the ratio of rapid isometric HAM versus QUAD torque production (rate of torque development (RTD)) assessed over shorter time frames (<200 ms) has been proposed as a relevant measure of dynamic knee joint stabilization.
Explosive strength is quantified by the RTD during a maximal voluntary isometric contraction (MVC) and can be separated into the RTD observed in the very early phase of the MVC (0–100 ms), also denoted as the initial RTD, and the RTD generated in the later phase of rising muscle force (late RTD), which is defined by the RTD developed from the onset of the MVC to a period between 100 and 200 ms. In addition, the HAM/QUAD strength ratio (H/Q ratio) has been used to assess dynamic knee joint stabilization potential both in alpine ski racers and in other athlete populations. Furthermore, because initial RTD, late RTD, and maximum muscle strength are relevant to dynamic athletic performance and can be developed by specific training methods, assessment of these strength characteristics may provide important information for optimizing the design of rehabilitation and resistance training programs in ski racers returning from ACL injury.
Because of the unique characteristics of noncontact ACL injury in elite ski racers, the risk for ACL injury/reinjury, the importance of HAM and QUAD muscle strength for ski performance and injury prevention, and the lack of scientific data on thigh muscle strength in actively competing elite ski racers with/without ACL injury, the aim of the present investigation was to perform a comprehensive HAM and QUAD muscle strength assessment and to evaluate lower limb muscle mass in a group of actively competing elite alpine ski racers with/without ACL-R. We hypothesized that the ACL-R skiers would demonstrate significant deficits in the ACL-R limb for muscle mass, HAM strength, and QUAD strength, both compared with the contralateral limb and with the limb average of uninjured elite skiers (control group). In addition, in uninjured individuals, we expected female skiers to demonstrate reduced thigh muscle strength compared with that in male skiers and no signs of bilateral limb strength deficits in both genders.
Abstract and Introduction
Abstract
Purpose Because of the importance of hamstrings (HAM) and quadriceps (QUAD) strength for anterior cruciate ligament (ACL) injury prevention and the high incidence of ACL injury in ski racing, HAM and QUAD maximal and explosive strength were assessed in ski racers with and without ACL reconstruction (ACL-R).
Methods Uninjured (n = 13 males, n = 8 females) and ACL-R (n = 3 males, n = 5 females, 25.0 ± 11.3 months after operation) elite ski racers performed maximal voluntary isometric HAM and QUAD contractions to obtain maximal torque (MVC) and rate of torque development (RTD) at 0–50, 0–100, 0–150, and 0–200 ms. MVC and RTD (per kilogram body mass) were calculated for the uninjured group to compare between sexes and to compare the control group with the ACL-R limb and unaffected limb of the ACL-R skiers. HAM/QUAD MVC and RTD strength ratios (H/Q ratios) were also compared.
Results The ACL-R limb demonstrated significant HAM and QUAD deficits compared with the contralateral limb for MVC and late-phase RTD (P < 0.05). Uninjured male skiers also displayed a limb difference for HAM MVC and RTD at 150 ms (P < 0.05). QUAD MVC and RTD deficits were observed in the affected limb of ACL-R skiers, which led to an inflated H/Q ratio (50 ms) compared with that in uninjured controls (P < 0.05). Compared with male skiers, females displayed greater relative HAM RTD (50 ms) and an elevated H/Q RTD ratio (50 ms), suggesting enhanced ACL protection (P < 0.05).
Conclusions Because of the strength demands of ski racing, our results suggest the importance of including HAM and QUAD strength assessments in the physical evaluation of uninjured skiers. Furthermore, HAM and QUAD strength should be assessed over a long-term period after surgery to identify chronic strength deficits in ACL-R ski racers.
Introduction
Elite alpine ski racing is a physically demanding sport involving high speeds and large external loads imposed on the lower limbs that occur in an unpredictable environment. Skiers perform repeated bidirectional turns with forceful eccentric muscle contractions, which typically involve maximal levels of neuromuscular activity in the thigh muscles. To meet these demands, elite alpine ski racers display high levels of hamstrings (HAM) and quadriceps (QUAD) strength, an elevated HAM/QUAD strength ratio (H/Q ratio), and marked bilateral strength symmetry.
Because of the extreme demands of elite alpine ski racing, there is a high risk for lower body injury, especially to the knee joint. In a competitive season, knee injuries accounted for over 30% of the injuries experienced by elite alpine ski racers, and more than half of these injuries resulted in a significant time loss from sport (>28 d). Anterior cruciate ligament (ACL) rupture is the most common form of serious knee joint injury in ski racing, accompanied by a high ACL reinjury rate. Research into the mechanisms and etiology of noncontact ACL injury in elite alpine ski racing highlights distinct differences compared with ACL injury in field sports, including several mechanisms of high-force injury. Furthermore, at the elite level, no sex differences in ACL injury rates are found, which is attributable to the preclusion of sex-related risk factors due to the high force/energy injury mechanisms.
To achieve effective injury prevention, it is important to identify modifiable risk factors that can be targeted through exercise and training. However, to date, only a single scientific study has been conducted that was aimed at assessing the relationship between modifiable (trainable) risk factors and ACL injury in ski racers, suggesting that core strength deficits were associated with injury in young competitive ski racers. However, more senior elite ski racers may be at an even greater risk for ACL injury. Not only is there a paucity of scientific literature on trainable risk factors for ACL injury prevention in elite alpine ski racers, but also, there are no studies on ACL reinjury prevention in actively competing ski racers with a history of ACL injury and ACL reconstruction (ACL-R).
After ACL injury, the primary objective is to restore QUAD and HAM muscle strength. Thigh muscle strength deficits have been associated with a successful return to sport and activity. Restoring thigh muscle strength is especially important for ACL-R ski racers because of the importance of QUAD strength in ski racing and the influence of HAM/QUAD strength imbalance on knee injury risk. However, long-term HAM and QUAD strength deficits often persist despite rehabilitation, and because coordinated HAM and QUAD muscle function is important for ACL protection, identifying strength deficits is important.
Several measures of HAM and QUAD muscle strength have been proposed for their clinical efficacy. However, because of the short time history of noncontact ACL injury in field sports (<50 ms after foot contact), the assessment of maximal HAM and QUAD strength, which often requires more than 300 ms to develop under isometric conditions, has been questioned. Instead, the ratio of rapid isometric HAM versus QUAD torque production (rate of torque development (RTD)) assessed over shorter time frames (<200 ms) has been proposed as a relevant measure of dynamic knee joint stabilization.
Explosive strength is quantified by the RTD during a maximal voluntary isometric contraction (MVC) and can be separated into the RTD observed in the very early phase of the MVC (0–100 ms), also denoted as the initial RTD, and the RTD generated in the later phase of rising muscle force (late RTD), which is defined by the RTD developed from the onset of the MVC to a period between 100 and 200 ms. In addition, the HAM/QUAD strength ratio (H/Q ratio) has been used to assess dynamic knee joint stabilization potential both in alpine ski racers and in other athlete populations. Furthermore, because initial RTD, late RTD, and maximum muscle strength are relevant to dynamic athletic performance and can be developed by specific training methods, assessment of these strength characteristics may provide important information for optimizing the design of rehabilitation and resistance training programs in ski racers returning from ACL injury.
Because of the unique characteristics of noncontact ACL injury in elite ski racers, the risk for ACL injury/reinjury, the importance of HAM and QUAD muscle strength for ski performance and injury prevention, and the lack of scientific data on thigh muscle strength in actively competing elite ski racers with/without ACL injury, the aim of the present investigation was to perform a comprehensive HAM and QUAD muscle strength assessment and to evaluate lower limb muscle mass in a group of actively competing elite alpine ski racers with/without ACL-R. We hypothesized that the ACL-R skiers would demonstrate significant deficits in the ACL-R limb for muscle mass, HAM strength, and QUAD strength, both compared with the contralateral limb and with the limb average of uninjured elite skiers (control group). In addition, in uninjured individuals, we expected female skiers to demonstrate reduced thigh muscle strength compared with that in male skiers and no signs of bilateral limb strength deficits in both genders.
