Martin Mc Intyre (PhD., M.Med.Sci., MSc., BSc) is the CEO and Founder of the HRIG. He has 20 years of working in high performance sport has completed his PhD through John Moores University, Liverpool where he focused specifically on strength and its relationship to hamstring injury.
Isometrics first began back in BC with the Yogis in cave dwelling’s been depicted in certain isometric poses and following this Buddhist monks exposed their bodies from both a physical and spiritual perspective, with certain isometric poses. Were they both ahead of their time?
Isometrics have done somewhat of a U turn over the last decade and are now again favoured as they achieve high motor unit recruitment, are associated with less DOMS and mechanical damage thus quicker recovery, and train targeted muscle length to elicit gains in performance and injury prevention.
Isometric emanates from the Greeks and translates to “equal measuring. Modern day interpretation of this has been undertaken with the presumption and categorisation that the muscle contraction remains static in which
there is equilibrium and static contraction of muscle fibers. However the assumptions associated with this mode of contraction are questionable. At microscopic level, rarely if ever does either, the in-series elastic structures or the various fascicle orientations and lengths provide the force output through “static” or “isometric” conditions. During which the MTU and muscle fibers can shorten by up to 28% (Griffiths et al., 1991). Tendon creep also occurs
whereby the tendon lengthens and the muscle fibers shorten (Mademli, 2005). We also now know that various regions within the hamstring possess areas of region specific fascicle lengths (Fiorentino et al., 2014) and from our clinical and PhD research this can range between 6-13cm.
Within this arrangement from the proximal to distal segments it could be hypothesized that the synergism of these fascicles place various areas of load distributions throughout the hamstrings. This would obviously be influenced by hip and knee joint angles and the mode of exercise.
The ambiguity of the term “isometric’ can be related to 1) the joint position and 2) mechanical output of the hamstrings. Joints are isometric and static, however it is clear the contraction is dynamic both at MTU and microscopic level. It therefore might be worth considering a more relevant term as Isodynamic (IsoDyn) to describe the shortening and lengthening of these elastic components.
To expand this further IsoDyn rehabilitation can been expanded to consist of
One such device to develop these concepts, specifically in relation to the stance and late swing of the gait cycle is the, HRIG. Tests have been standardised to assess maximum voluntary force isometric function in this sprint specific position which has a high rate of both inter and intra-rate reliability (Mc Intyre, 2023). These tests have been associated with previous and prospective injury risk and hamstring BAMIC classification, following acute injury. More-over this device has been developed further to load ISODyn function.
Figure 1. Sprint specific ISODyn Assessment with the HRIG
Interestingly IsoDynCON is undertaken in a position specific to late swing and early stance in which the MTU is placed in a vulnerable lengthened position at 1500 of knee extension and by creating a lever arm through the contralateral hip, in 200 of extension. As in figure 2, in the initial stage of IsoDynCON the hamstring complex elicits a IsoDynCON by contraction of the MTU and elastic/fascicle muscle fibre orientation: (1) Following this the MTU/Elastic/Fascicle elements are seen to work dynamically which is represented by the oscillation in the force trace (2) Finally the end stage of 9 second contraction they now work in tandem to dissipate force whilst still remaining in this isometric late swing/early stance position (3).
Figure 2 . IsoDynCON is undertaken in a position specific to late swing and early stance
IsoDynBALL and IsoDynRE force is illustrated in Figure 3. Again during the initial stages of both the ballistic and reactive contractions the MTU is working to produce force effectively and rapidly (0.1ms): (1) Whilst during the reactive phase (2) The hamstring complex is working dynamically to attenuate/decelerate force and finally generate a horizontal propulsion force once again
Figure 3. IsoDynBALL and IsoDynRE facilitates rate of force development training with respect to the MTU.
Early loading following acute muscle injury has been reported to accelerate RTP (Bayer et al., 2017). The HRIG has been used to maximise and accelerate return to play 44 days post Bicep Femoris “3c” hamstring injury with return to run, return to modified training and return to full training achieved on days 19, 39 and 45 respectively, as illustrated in Figure 4 (McIntyre et al., 2024). This study may impact future prognosis, rehabilitation and inform return to play decision making and loading. The introduction of a ramped isometric protocol safely loads muscle-tendon injuries and may improve expected recovery rates (Power et al., 2023). With an increase and an increased detection for “C” type injuries the relevance of the proximal geometry is been researched and debated. The aponeurosis is an important component of this complex since larger aponeuroses and smaller muscle to aponeurosis volume ratios, are related to hamstring strain injury (Balshaw et al., 2024 ; Lazarczuk et al., 2024).
Figure 4. Effect of a ramping HRig protocol on HRIG metrics.
Interestingly Isodynamic loading in this HRIG position specific to the mechanism may help mitigate against injury and protect this troublesome region by specifically loading the MTU. The late swing/early stance phase of running account for 40-70% of all hamstring muscle injuries and this mechanism is widely dependant on the sport (Australian Rules, Soccer, GAA, Rugby).One has also to consider the contracting element increasing, decreasing and recoiling to return stored energy and possibly even working isometrically prior, during and after foot strike (Thelen et al., 2005a, Van Hooren and Bosch, 2017, Chumanov et al., 2012). The strength of the muscle and its ability to withstand eccentric and isometric force in the late swing and the transition to early stance highlights the importance of an effective contractive synergy at microscopic level. Injury prevention is not only reserved to increasing the strength and capacity of the muscle fibers but the interaction of the MTU and its ability to produce and tolerate force. Does this facilitate aponeurosis robustness, accelerate return to play,
reduce re-injury rates and effectively load athletes? Maybe, the YOGI‘s and Buddihist’s are leading us ‘Back to the Future”.