riceps strength (HIQ for flexion) may provide a more functional estimate of the capacity for muscular knee joint stabilization. (1 ). Based on peak moment and 50" ...
Training and Testing
lsokinetic Muscle Strength and Capacity for Muscular Knee Joint Stabilization in Elite Sailors P Aagaard !E. B. Simonsen2, N. Beyer3, B. Larsson ',P. Magnusson ', M. vier3 Team Denmark Testcenter. Department of Exercise Physiology lTA-2001, Rigshospitalet (University Hospital), Copenhagen. Denmark Institute of Anatomy C. Panum Institute. University of Copenhagen Department of RheumatologyH, Bispebjerg Hospital, University of Copenhagen
P.Aagaard, E. 8. Sirnonsen. N. Beyer,B. lnrsson. F! Magnusson. M. IOzc lsokinetic Muscle Strength and Capacity for Muscular Knee Joint Stabilization in Elite Sailors, Int. J. Sports Med., Vol. 18. pp. 521 - 525,1997.
high maximal quadriceps strength and partially lower (SF) conventional H/Q ratios. Key words: Isokinetics, quadriceps, hamstrings, H/Q ratio, knee joint, elite sailing
Accepted after revision: March 17,1997 Introduction In the present study isokinetic dynamometry was used t o evaluate the capacity for dynamic knee joint stabilization via muscle contraction In elite sailors (15 males. SM: 6 females. SF) compared t o a group of matched controls (8 males, CM). Maximal concentric, eccentric and isometric moment of force (peak moment and moment at 50" knee flexion) was obtained for the knee extensors (quadriceps) and flexors (hamstrings) during isokinetic knee joint movement at angular velocities 0,30, High levels of eccentric knee extension 120 and 180"-~-~. strength were observed for the elite sailors compared t o the controls ( p < 0.05). Based on peak moment and 50" moment, respectively. conventional hamstring/quadriceps (H/Q) strength ratio (kSD) ranged from 0.37 k0.06 t o 0.54f 0.06 and from 0.42i0.07 t o 0.57 k0.10 across groups, speed and contraction mode. The female elite sailors displayed lower (p < 0.05)concentric H/Q ratios at 120 and 180".s-' compared t o the controls (0.41 -0.45 vs. 0.51-0.56,respectively). The ratio of eccentric hamstring t o concentric quadrlceps strength (H/Q for extenslon) or concentric hamstring t o eccentric quadriceps strength (HIQ for flexion) may provide a more functional estimate of the capacity for muscular knee joint stabilization (1 ). Based on peak moment and 50" moment. respectively, this "functional" H/Q ratio ranged from 0.24 0.03 and 0.25 0.02 for knee flexion at 180"-s-I t o 0.97+0.17 and 0.88+0.12 for knee extension at 180"-~-~ among the three groups. Comparable levels of "functional" H/Q ratio were observed (p> 0.05) for fast knee extension i n the elite sailors (S~:0.81-0.97,SM: 0.88-0.95) and the male controls (CM: 0.80-0.84). In conclusion. a "functional" H/Q ratio of 0.8-1.0 observed for all subjects indicated a significant functional capacity of the hamstring muscles for providing muscular stability at the knee joint in fast knee extenslon. A significant potential for muscular knee joint stabilization appeared for the elite sailors despite thelr
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lnt. J. Sports Med. 18 (7997) 521 -525 0 CeorgThieme Verlag Stuttgart . New York
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With several Olympic class boat types (Finn. 470, Soling) the sailor hang over the side o f the boat supported by the leg and trunk muscles to allow for more wind to fill the sails. I n the most effective hiking postures the sailor is exposed to large knee extensor and trunk flexor loads (13). Consequently, elite sailors may display very high eccentric and isometric knee extensor (m.quadriceps) strength together w i t h average-to-norma1 levels of maximal knee flexor (hamstring) strength (3). The lack o f elevated hamstring strength levels could indicate that the reciprocal knee flexor/extensor strength relationship is shifted towards quadriceps dominance i n elite sailors. Such relative hamstring muscle strength deficit may i n some situations be detrimental for the knee joint, for instance when active knee extension is accompanied by a reduced antagonist muscle tone (5). For the human knee joint it is well established that quadriceps muscle contraction itself is capable of creating an anterior directed shear of the tibia relative to the femur (11,12). Large stress forces may consequently be imposed on the anterior cruciate ligament (ACL) (6.8.14). However. the ACL strain induced by quadriceps contraction can be reduced through co-contraction o f the hamstring musculature (8,14). Therefore it is o f interest to evaluate the physiological capacity o f the hamstring muscles in contributing to knee joint stability via such co-contraction mechanisms. lsokinetic hamstring1 quadriceps strength ratio is by convention calculated as maximal hamstring contraction strength (moment of force) divided by maximal quadriceps contraction strength for a given angular velocity and contraction mode (isometric, concentric, eccentric) (1,lO).However, conventional HIQratio offers no vital information on the muscle potential for dynamic stabilization during actual knee joint movements. The HIQratio of eccentric hamstring to concentric quadriceps strength (H/Q for extension) or concentric hamstring to eccentric quadriceps strength (H/Q for flexion) may provide a more "functional" estimate o f the capacity for muscle stabilization about the knee joint (1). In a previous study w e found conventional H/Q ratio to be 0.45 - 0.55 across contraction modes (con, ecc, isom) and an-
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Int. I. Sports Med. 18 (1997)
gular velocities while in contrast "functional" H/Q ratio was approximately 1.00 for fast knee extension (240". s-I) indicating a 1 : 1 hamstring/quadriceps strength relationship during this condition (I). Moreover, we recently found that heavy-resistance strength training resulted in an increased "functional" H/Qratio to well above 1.00 for fast knee extension (240". s-I), which indicated an enhanced capacity of the hamstring muscles to provide stability to the Itneejoint during fast and forceful extension (2). The "functional" H/Q ratio for knee flexion, Hcon/Qc,,which is noticeably low (about 0.30) a t the fastest angular velocities examined (1,2), on the other hand suggests the hamstring muscles to have only a limited capacity for dynamic knee joint stabilization during forceful knee flexion movements. It is suggested that a sensitive and simple evaluation of dynamic knee joint function can be achieved by combining the data on "functional" H/Qratio, conventional H/Qratio and maximal eccentric and concentric muscle strength. The aim of the present study was to evaluate the capacity for muscular Itnee joint stabilization in a group of subjects (elite sailors) who were characterized by high levels of maximal quadriceps strength (3). In terms of a working hypothesis a diminished capacity for dynamic knee joint stabilization was expected for the sailor subjects, as a result of their high quadriceps strength levels and apparant relative hamstring deficit.
P.Aogaord. E. 6. Simonsen. N. Beyer et ol.
moments were obtained at 50" knee flexion to allow the criterion of constant knee angular velocity to be fulfilled, also at the highest velocities examined (1). Isometric moments were all measured at 65" knee flexion (1). Moments were corrected for the effect of gravity on the shank, foot and ankle-pad (1). lsokinetic H/Q strength ratio Conventional H/Q ratio was calculated according to its formal definition by dividing maximal isokinetic hamstring (knee flexor) strength by maximal quadriceps (knee extensor) strength fora given contraction mode and joint angular velocity.
"Functional" H/Q ratio representative for knee extension was defined as the ratio of maximal eccentric hamstring strength relative to maximal concentric quadriceps strength (H,,,/Qon) for a given joint angular velocity (1). "Functional" H/Q ratio representative for knee flexion was defined as the ratio between maximal concentric hamstring strength and eccentric quadriceps strength (H,,/Q,,) (1).
H/Qratios were calculated based on both peak moment and constant-angle moment (50" knee angle). Statistics
Material and Methods
Subjects Twenty-one elite sailors (6 females: group SF,15 males: group SM)and a group of control subjects (8 males: CM)volunteered to participate in the study. Mean body mass and height (k SD) were 67.2 5.9 kg (SF),81.7 ? 13.1 kg (SM),76.5 ? 5.6 kg (CM)and 1.72 + 0.11 m (SF),1.83 ? 0.06 m (SM),1.83 k 0.07 m (CM),respectively. All subjects gave their informed consent to the conditions of the experimental procedures. The control subjects, who were physical education students without prior experience in systematic strength training, were comparable to the male sailors in age, anthropometry and level of fitness. All subjects gave their informed consent to the conditions of the experimental procedures.
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Measurement of isokinetic muscle strength Isoltinetic joint moment was obtained by use of a Kin-Com dynamometer (Icinetic Communicator, Chattecx Corp., Chattanooga. USA). All measurements were preceded by a preconditioning to the dynamometer and the testing procedures. Successive trials were performed at each angular velocity with 15-45 seconds rest intervals until the subject was unable to increase peak moment further. Subjects were seated 10" reclined and firmly strapped at the hip and thigh. The rotational axis of the dynamometer was visually aligned with the lateral femoral condyle. The lower leg was attached to the load cell of the dynamometer superior to the medial malleolus. Isometric. and moment at concentric and eccentric peak moment (M), 50' knee angle (MSo)(OO=fullextension) were obtained at knee angular velocities 0,30.120 and 180"-s-I through a 1090" range of movement (0" = knee fully extended). Due to basic methodological disparities between the measurements of peak moment and constant-angle moments (1) were H/Q ratios calculated from both in the present study. Constant-angle
Inter-group comparisons were tested by Kruskall-Wallis oneway analysis of variance for unpaired samples (Siege1 & CastelIan 1988). Intra-group variation in H/Qratio across knee angular velocjties and contraction modes (concentric, eccentric) was evaluated by the Friedman two-way analysis of variance by ranks for related samples with repeated measures (15). All tests were two-tailed at a p = 0.05 level of significance. Results
Knee extension and flexion strength The levels of maximal isoltinetic knee extensor and flexor strength in the three groups of subjects are shown in Fig. 1. As can be seen eccentric knee extension strength was higher in male sailors compared to male controls. Also, isokinetic Itnee joint strength generally was lower in female sailors compared to male sailors. The levels of maximal eccentric knee extensor and flexor strength observed in the female sailors were however not significantly different from those of the male controls (Fig. I). H/Q strength ratio
Based on peak moments conventional H/Q ratio (kSD) ranged from 0.41 r 0.07 to 0.51 5 0.08, 0.37 2 0.06 to 0.52 20.05 and 0.43 k 0.05 to 0.54 k 0.06 in SM,SFand CM,respectively (Fig. 2a. Table 1A). Based on 50"-moments conventional H/Q ratio ranged from 0.48 k0.06 to 0.52 2 0.13,0.42 & 0.07 to 0.47 & 0.05 and 0.51 ? 0.03 to 0.57 ? 0.10 in SM,SF and CM,respectively (Fig. 2 B, Table 1 A). Concentric conventional H/Q ratio was lower in SF compared to SM and CM at 120 and 180O.s-I ( p i0.05, Table I A). Based on peak moment "functional" H/Q ratio ranged from 0.28 0.06, 0.24 k 0.03,0.34 f 0.06 for knee flexion at 180". s-'
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Int.]. Sports Med. 18 (1997)
Dynamic Knee joint Stabilization
Table 1 A Conventional isokinetic hamstring/quadriceps strength ra-
lsokinetic Strength
-
A
k n e e extensors (A,=) flexors (a,n)
tio for concentric, eccentric and isometric muscle contraction, based on peak moment and 50" moment.
. .
Velocity ('. s-')
A
.
0
Peak m a m e n l 50' mornenl
SMgroup
SF group
CMgroup peak 50"
s 5
SM (male sailors) Lu-.
S
o"3BS
'n.nnl
peak 50" peak 50" peak 50"
1
eccenlric
- II
.
I
.
I
-180-120
'
concentric
I
"30
peak 50"
.
I
.
30
I
'
CM
peak 5 0"
I
120
180
peak 5 0"
(male controls) -.@R€--
Conventional H/Q ratio (percent+SD) in male and female elite sailors (SM, Sf) and male controls (CM) based on peak moment and 50" moment, calculated for eccentric (- 30. - 120, - 240'. s-'), isometric (isom) and concentric (30.120. 240'. sml) muscle contraction. *: Sr < SM,CM (p ~ 0 . 0 5 ) .
**
Table 1 B 'Functionol" isokinetic hamstringlquadriceps strength ratio eccenlric
0
-100-120
representative for knee extension, knee flexion and isometric muscle contraction, based on peak moment and 50" moment.
concenlric
-30
30
120
180
Velocity (". s-')
Su group
SF group
CMgroup
SF (female sailors)
5 300
peak 50" peak 50" peak 50" peak 50"
1 0
1
concenlric
eccenlric .
1
.
,
-180-120
knee
.
,
-30
.
30
1
.
1
.
120
peak 50"
1
I00
peak
angular velocity ("/set)
Flg.1 Maximal isokinetic moment of force for knee extension (filled symbols) and flexion (open symbols) in male and female elite sailors (top and bottom panels, respectively) compared t o a group of male controls (mid panel). Peak moments (triangles) and constant-angle moment at 50' knee flexion (boxes) are shown. For simplicity standard deviations are not shown. Group differences: top panel ' S M > C M (p < 0.05). mid panel CM> SF(p < 0.05).
to 0.95 t 0.16, 0.97 t 0.17, 0.84 ? 0.15 for knee extens~onat 180" .s-' in SM,SF and CM, respectively (Fig. 2A, Table 1B). Based on 50"-moments "functional" H/Q ratio ranged from 0.30 r 0.07, 0.25 50.02 and 0.38 k 0.09 for knee flexion at 180". s-I to 0.88 f 0.12, 0.81 + 0.17 and 0.80 f 0.14 for knee extension at 180"-s-' (Fig.2B,Table 1B). Based on peak moment "functional" H/Q ratio for knee flexion (Ha,/%,) was lower in S~comparedto SMand CMat angular velocity 30" s-I ( p < 0.05), and lower in SF and SM compared to CM at angular velocities
50" peak 50" "Functional"H/Q ratio (percent? SD) In male and female elite sailors (SM. SF) and male controls (CM) based on peak moment and 50" moment. for knee flexion (- 30. - 120. - 2 4 0 " . s-I). knee extension (30.120.240". s-I) and isometric muscle contraction (isom). ': SF, SM
