Conventionally, the hamstring:quadriceps strength ratio is calculated by dividing the maximal knee flexor (hamstring) moment by the maximal knee extensor (quadriceps) moment measured at identical angular velocity and contraction mode. The agonist-antagonist strength relationship for knee extension and flexion may, however, be better described by the more functional ratios of eccentric hamstring to concentric quadriceps moments (extension), and concentric hamstring to eccentric quadriceps moments (flexion). We compared functional and conventional isokinetic hamstring: quadriceps strength ratios and examined their relation to knee joint angle and joint angular velocity. Peak and angle-specific (50 degrees, 40 degrees, and 30 degrees of knee flexion) moments were determined during maximal concentric and eccentric muscle contractions (10 degrees to 90 degrees of motion; 30 and 240 deg/sec). Across movement speeds and contraction modes the functional ratios for different moments varied between 0.3 and 1.0 (peak and 50 degrees), 0.4 and 1.1 (40 degrees), and 0.4 and 1.4 (30 degrees). In contrast, conventional hamstring:quadriceps ratios were 0.5 to 0.6 based on peak and 50 degrees moments, 0.6 to 0.7 based on 40 degrees moment, and 0.6 to 0.8 based on 30 degrees moment. The functional hamstring:quadriceps ratio for fast knee extension yielded a 1:1 relationship, which increased with extended knee joint position, indicating a significant capacity of the hamstring muscles to provide dynamic knee joint stability in these conditions. The evaluation of knee joint function by use of isokinetic dynamometry should comprise data on functional and conventional hamstring:quadriceps ratios as well as data on absolute muscle strength.

Equivocal findings exist on the effect of concurrent strength (S) and endurance (E) training on endurance performance and muscle morphology. Further, the influence of concurrent SE training on muscle fiber-type composition, vascularization and endurance capacity remains unknown in top-level endurance athletes. The present study examined the effect of 16 weeks of concurrent SE training on maximal muscle strength (MVC), contractile rate of force development (RFD), muscle fiber morphology and composition, capillarization, aerobic power (VO2max), cycling economy (CE) and long/short-term endurance capacity in young elite competitive cyclists (n=14). MVC and RFD increased 12-20% with SE (P<0.01) but not E. VO2max remained unchanged. CE improved in E to reach values seen in SE. Short-term (5-min) endurance performance increased (3-4%) after SE and E (P<0.05), whereas 45-min endurance capacity increased (8%) with SE only (P<0.05). Type IIA fiber proportions increased and type IIX proportions decreased after SE training (P<0.05) with no change in E. Muscle fiber area and capillarization remained unchanged. In conclusion, concurrent strength/endurance training in young elite competitive cyclists led to an improved 45-min time-trial endurance capacity that was accompanied by an increased proportion of type IIA muscle fibers and gains in MVC and RFD, while capillarization remained unaffected.

Whether the cross-sectional area (CSA) and mechanical properties of the human Achilles tendon change in response to habitual exercise remains largely unexplored. The present study evaluated the CSA and contraction-induced displacement of the aponeurosis-tendon complex of the triceps surae in 11 untrained subjects before (tests 1 and 2) and after (test 3) approximately 9 mo of regular running ( approximately 78 training sessions). Displacement of the tendon-aponeurosis complex obtained by ultrasonography; electromyography of the gastrocnemius, soleus, and dorsiflexor muscles; and joint angular rotation were recorded during graded isometric plantarflexion ramps. Tendon CSA and moment arm were measured by using MRI, and tendon force was calculated from joint moments and tendon moment arm. A treadmill test was used to determine submaximal oxygen consumption (Vo2) at a given speed and maximal Vo2. The total running duration was approximately 43 h, distributed over 34 wk. Maximal Vo2 increased 8.6% (P < 0.01), and submaximal Vo2 decreased 6.2% (P < 0.05). Tendon-aponeurosis displacement during maximal voluntary contraction was unchanged (tests 1-3, 5.2 +/- 0.6, 5.2 +/- 0.5, and 5.3 +/- 0.4 mm, respectively) and yielded a structural stiffness of 365 +/- 50, 358 +/- 40, and 384 +/- 52 N/mm for tests 1-3, respectively (P > 0.05). Tendon CSA also remained unchanged (tests 1-3, 34.2 +/- 2.2, 33.9 +/- 2.2, and 33.8 +/- 2.1 mm2, respectively). In conclusion, a total training stimulus of approximately 9 mo of running in previously untrained subjects was adequate to induce significant cardiovascular improvements, although it did not result in any changes in the mechanical properties of the triceps surea tendon-aponeurosis complex or in the dimensions of Achilles tendon.

Muscle fiber size and mechanical muscle performance, particularly RFD, were consistently elevated in aged individuals exposed to chronic (i.e., lifelong) strength training. This relative preservation in muscle morphology and function may provide an important physical reserve capacity to retain muscle mass and function above the critical threshold for independent living at old age.