I found the following quite interesting. Do read the full article.
http://www.pponline.co.uk/encyc/0681.htm
Returning to our friends the turkeys, whenever they ran on a 12deg. incline their calf muscles were appreciably longer during the early stage of footstrike than when running on a flat surface. The same thing happens to you when you run on a hill; the inclination of the hill thwarts plantar (downward) flexion of your ankles prior to impact and dorsiflexes your ankles for you as your feet hit the ground, keeping your calf muscles stretched. The result is that your over-stretched calf muscles must shorten more during the stance phase of incline running in preparation for toe-off than is necessary when running on the flat.
Hill running is not anti-neural
This increased shortening greatly magnifies the net work per step performed by the calf muscles, and the same magnification of work output would occur in the hamstrings. The increase in muscular work associated with incline running is linked with the activation of a greater number of calf-muscle fibres. In fact, EMG data on the turkeys suggested that running up a 12deg. slope required three times the volume of calf-muscle fibres than level running at the same speed. Interestingly enough, stance time did not increase during incline running, which indicates that the average rate of shortening of the calf muscle actually increased with inclination. This is important, since critics of hill running have argued that it is ‘anti-neural’ - ie that it slows down muscular movement and the rate at which muscles are recruited by the nervous system. The turkey data show that, at a specific speed, crucial running muscles like those of the calves actually contract more quickly on hills than they do on flat ground.
You might think that the young turks’ calf muscles produced more force in order to drive their bodies up the 12deg. ‘hills’ - especially since three times the volume of calf-muscle cells were involved per step. Far from it: their calves actually produced the same amount of force at 12deg. as they had on the level! If this seems surprising to you, you must have forgotten about the time-honoured force-velocity properties of muscles: as the velocity of muscle contraction increases, force production decreases. If this concept is a little wild for you, just think how much more quickly you can lift a barbell with 10lb attached than one with 100lb! Getting back to the turkeys’ calves, they were shortening more rapidly on hills, and this rapid shortening balanced the recruitment of extra muscle fibres, keeping force production constant. The increased work required for hill climbing was accomplished not via greater force production but via faster, longer contractions of the calves.
If this seems confusing as well, remember that muscular work equals force times distance (W = F X d). The Harvard-Northeastern scientists found that calf-muscle work per step increased on 12deg. hills, even though force (F) remained unchanged. What did change, of course, was d - the distance moved by (the change in length accomplished by) the calf muscle in its contractions during footstrike. With F unchanged and d spiked, work (W) increased significantly.
So, the calf muscles did more work by moving a greater distance during footstrike. In other words, on hills the calf muscles were learning to contract more quickly when the foot was on the ground. The calf muscles were not learning to generate more force - but to generate work at a higher rate. In short, they were learning to become more powerful. (Power is just work divided by time; in our turkey case, time - footstrike time - stayed the same, but work increased dramatically, causing power output to rise.)
On flat ground, this ability of the calf muscles to work more powerfully during footstrike should translate into shorter footstrike times and higher running speeds. Why shorter footstrike times? With the calf muscles reacting at a higher rate, the amount of work necessary to sustain a particular velocity could be performed in a shorter period of time, allowing toe-off to occur more rapidly. Alternatively, speed of contraction could be slowed but recruitment of ‘extra’ calf-muscle cells could be retained, enhancing force production and thus stride length. Naturally, the footstrike and stride-length pay-offs might occur simultaneously.
On hills, key muscles like the calves learn to sustain force at high contraction speeds. This defies the classic muscle force-velocity relationship principle, which states that muscles exert less force as their speed of action increases. Muscles accomplish this feat by recruiting extra fibres into action (three times as many in this study), which means that hill running has a very broad strengthening effect in addition to its ability to boost power. That’s an exciting aspect of hill training, and it is why the discipline is so fantastically useful for athletes who depend on high running speeds to do well in their sports. Football players, basketballers, rugby scrummers, cricket batsmen and fielders, and even runners - take note!
SWANSON, S. C., and G. E. CALDWELL. An integrated biomechanical analysis of high speed incline and level treadmill running. Med. Sci. Sports Exerc., Vol. 32, No. 6, pp. 1146–1155, 2000.
Purpose: Recent sprint training regimens have used high-speed incline treadmill running to provide enhanced loading of muscles responsible for increasing forward running speed. The goal of this study was to document the joint kinematics, EMG, and swing-phase kinetics of incline treadmill running at 4.5 m·s–1 with a 30% grade, and compare these data to that of level running under similar conditions.
Methods: Sagittal plane video (200 Hz) and EMG from eight lower extremity muscles were recorded during each of three locomotion conditions: incline running at 4.5 m·s–1 and 30% grade (INC), level running at 4.5 m·s–1 (LSS), and level running at the same stride frequency as INC (LSSF). A rigid body model was used to estimate net muscle power and work values at the hip, knee, and ankle during swing. Timing and amplitude of EMG signals for each muscle relative to footstrike were compared between conditions.
Results: Stride frequency and percentage of stride spent in stance were significantly higher during INC (1.78 Hz; 32.8%) than in the LSS (1.39 Hz; 28.8%) condition. Stride frequency played an important role, as most measures were more similar between INC and LSSF. Extensor range of motion of all joints during push-off was higher for INC. During INC, average EMG amplitude of the gastrocnemius, soleus, rectus femoris, vastus lateralis, and gluteus maximus were higher during stance, whereas the hamstrings activity amplitudes were lower. Average power and energy generated during hip flexion and extension in the swing phase were greatest during INC.
Conclusions: These data suggest that compared with LSSF and LSS, INC provides enhanced muscular loading of key mono- and bi-articular muscles during both swing and stance phases.
